THE    NUTRITION    OF    FARM    ANIMALS 


THE  MACMILLAN  COMPANY 

NEW  YORK   •    BOSTON   •    CHICAGO  •   DALLAS 
ATLANTA   •    SAN   FRANCISCO 

MACMILLAN  &  CO.,  LIMITED 

LONDON  •    BOMBAY  •    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


THE    NUTRITION 

OF 

FARM    ANIMALS 


BY 


HENRY   PRENTISS   ARMSBY,    PH.D.,    LL.D. 

•  i 

DIRECTOR  OF  THE  INSTITUTE  OF  ANIMAL  NUTRITION  OF  THE 
PENNSYLVANIA  STATE  COLLEGE;   EXPERT  IN  ANIMAL 
NUTRITION,  UNITED  STATES  DEPARTMENT  OF 
AGRICULTURE;     FOREIGN    MEMBER, 
ROYAL  ACADEMY  OF  AGRICUL- 
TURE OF  SWEDEN 


gork 

THE   MACMILLAN   COMPANY 
1917 

All  rights  reserved 


COPYRIGHT,  1917, 
BY  THE   MACMILLAN   COMPANY. 

Set  up  and  electrotyped.     Published  June,  1917. 

'  \  ) 


Nortoaoft 

J.  S.  Gushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

THE  manner  in  which  the  subject  of  the  nutrition  of  farm 
animals  is  presented  to  the  student  will  naturally  differ  ac- 
cording to  the  ultimate  end  in  view.  If  the  prime  purpose  is 
to  impart  practical  skill  in  the  feeding  of  live  stock,  the  study 
of  the  principles  of  nutrition  is  likely  to  be  regarded  as  pre- 
liminary and  to  partake  of  the  nature  of  an  information  course, 
and  chief  stress  will  be  laid  upon  familiarity  with  the  results 
of  experience,  particularly  as  related  to  the  business  aspects 
of  the  subject,  and  to  the  acquisition  of  practical  skill. 

But  while  by  no  means  disposed  to  minimize  the  significance 
of  this  aspect  of  the  subject,  the  writer  is  nevertheless  convinced 
that  for  the  students  of  our  agricultural  colleges  a  somewhat 
different  procedure  is  desirable.  He  believes  that  greater 
emphasis  than  they  sometimes  receive  may  wisely  be  laid  upon 
the  chemical  and  physiological  laws  which  underlie  the  practice 
of  feeding,  both  on  account  of  their  intrinsic  importance  and 
because  the  subject  may  thus  be  made  a  real  collegiate  disci- 
pline which  shall  contribute  to  the  training  as  well  as  to  the 
information  of  the  student. 

Accordingly,  the  present  volume  attempts  to  deal  primarily 
with  the  natural  laws  governing  the  nutrition  of  farm  animals, 
as  distinguished  from  the  broader  field  of  animal  husbandry, 
and  only  secondarily  with  the  specific  details  of  practice.  It 
seeks  to  avoid  so  far  as  may  be  mere  dogmatic  statements,  and, 
although  not  attempting  complete  citation  of  literature  even 
upon  important  points,  to  present  the  experimental  evidence 
with  sufficient  fullness  to  indicate  something  of  the  limitations 
of  present  knowledge  and  of  the  opportunities  for  further  in- 
vestigation. Its  aim  is  to  discuss  the  fundamental  principles 
upon  which  successful  stock  feeding  is  consciously  or  uncon- 
sciously based  in  the  firm  persuasion  of  the  truth  so  pithily 
expressed  almost  half  a  century  ago  by  the  father  of  agricul- 
tural science  in  the  United  States,  Professor  Samuel  William 

v 

380112 


VI  PREFACE 

Johnson,  that,  "Other  qualifications  being  equal,  the  more 
advanced  and  complete  the  theory  of  which  the  farmer  is  the 
master,  the  more  successful  must  be  his  farming.  The  more  he 
knows,  the  more  he  can  do.  The  more  deeply,  comprehen- 
sively, and  clearly  he  can  think,  the  more  economically  and 
advantageously  can  he  work,"  and  that  "A  true  theory  is  the 
surest  guide  to  a  successful  practice." 

In  short,  the  book  is  intended  for  the  student  rather  than 
directly  for  the  farmer  and  assumes  a  certain  degree  of  prelim- 
inary training  on  the  part  of  the  reader,  including  an  elementary 
knowledge  of  chemistry  and  physics. 

The  author  is  under  obligations  to  The  Honorable  Secretary 
of  Agriculture,  for  permission  to  reproduce,  in  Chapter  XVIII, 
a  part  of  Bulletin  No.  459  of  the  United  States  Department  of 
Agriculture;  to  the  Macmillan  Company  for  the  similar  use  in 
Chapter  XV  of  material  from  Bailey's  "Cyclopedia  of  American 
Agriculture";  and  to  Messrs.  Henry  and  Morrison  for  permis- 
sion to  base  the  tables  of  the  net  energy  values  of  feeding  stuffs 
contained  in  the  Appendix  upon  their  extensive  compilations 
in  the  fifteenth  edition  of  "Feeds  and  Feeding."  He  is  like- 
wise indebted  to  the  following  publishers  for  the  use  of  the  cuts 
named : 

The  Carnegie  Institution  of  Washington,  Figure  24. 

The  F.  A.  Davis  Company,  Figure  17. 

Ginn  &  Company,  Figures  2,  3,  6,  7,  8,  16,  19,  20,  and  22. 

The  Macmillan  Company,  Figures  4,  15,  29,  31,  32,  33,  34, 
37,  43,  44,  and  45. 

The  W.  B.  Saunders  Company,  Figures  1,5,  and  14. 

John  Wiley  &  Sons,  Inc.,  Figures  18  and  40. 

STATE  COLLEGE,  PA., 
May,  1917. 


CONTENTS 

PAGE 

INTRODUCTION vii 

PART  I 
THE  MATERIALS  OF  NUTRITION 

CHAPTER   I 

THE  COMPONENTS  OF  PLANTS  AND  ANIMALS 3 

§  i.  Dry  matter;  organic  matter ;  ash 3 

§  2.  The  carbohydrates 7 

§  3.  Fats  and  related  bodies.  —  The  Lipoids         .         .         .         .16 
§  4.  The  proteins ........  .24 

§  5.  The  non-proteins 36 

§  6.  Sundry  ingredients         .         .         .    *    .         .        .         .        -39 

CHAPTER  II 

THE  COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS         .        .      42 

§  i.  The  cell 42 

§  2.  Animal  tissues  and  organs 45 

§  3.  The  composition  of  £he  animal  as  a  whole     .         .         .         .61 
§  4.  The  composition  of  feeding  stuffs 66 

PART  II 
THE  PROCESSES  OF  NUTRITION 

CHAPTER  III 

DIGESTION  AND  RESORPTION      .        .        .        .        .        .        .        -77 

§  i.  The  organs  of  digestion 77 

§  2.  The  chemistry  of  digestion    .......      89 

§  3.  Resorption  —  The  feces 105 

§  4.  The  determination  of  digestibility in 

vii 


Vlll  CONTENTS 

CHAPTER  IV 

PAGE 

CIRCULATION,  RESPIRATION,  AND  EXCRETION 123 

§  i.  Circulation    ..........  123 

§  2.  Respiration 132 

§  3.  Excretion 139 

CHAPTER  V 

METABOLISM 144 

§  i.  General  conception        .         .         .         .         .        .        .        .144 

§  2.  Enzyms  as  agents  in  metabolism  .         .         .         .         .         .148 

§  3.  The  metabolism  of  the  carbohydrates 152 

§  4.  The  metabolism  of  the  simple  proteins  .         .         .         .         .160 
§  5.  The  metabolism  of  the  nucleoproteins  .         .         .         .         .168 

§6.  The  metabolism  of  the  fats .171 

§  7.  Metabolism  of  ash  ingredients 178 

§  8.  Functions  of  the  nutrients 182 

CHAPTER  VI 

THE  BALANCE  OF  NUTRITION 192 

§  i.  General  conception         .         . 192 

§  2.  Methods  of  investigation 194 

§  3.  The  balance  of  matter  . 202 

§  4.  The  balance  of  energy   . 216 

§  5.  Significance  of  results 241 


PART   III 
THE  FEED   REQUIREMENTS 

CHAPTER  VII 

THE  FASTING  KATABOLISM 249 

§  i.  The  protein  katabolism  in  fasting 251 

§  2.  The  energy  katabolism  in  fasting  .         .         .         .         .         .256 

§  3.  Conditions  affecting  the  fasting  katabolism  .         .         .         .258 


CONTENTS  ix 

CHAPTER  VIII 

•  PAGE 

MAINTENANCE  —  THE  ENERGY  REQUIREMENTS          .        .        .        .267 

§  i.  Net  energy  values  for  maintenance 271 

§  2.  Maintenance  requirements  of  farm  animals  .  .  .  .280 
§  3.  Factors  affecting  the  maintenance  requirement  .  .  .  304 
§  4.  The  relation  of  the  maintenance  requirement  to  external 

temperature 3°8 

CHAPTER  IX 

MAINTENANCE  (Continued) — THE  REQUIREMENTS  OF  MATTER         .  313 

§  i.  The  protein  requirements  for  maintenance    .         .         .         .  313 

§  2.  The  ash  requirements  for  maintenance 332 

§  3.  Accessory  substances 348 

CHAPTER  X 

THE  FATTENING  OF  MATURE  ANIMALS 35° 

§  i.  Composition  of  the  increase  in  fattening  .  .  .  -35° 
§  2.  Feed  requirements  for  fattening  ......  359 

CHAPTER  XI 

GROWTH 37i 

§  i.  General  nature  of  growth       .         .         .         .         .         .         .     371 

§  2.  The  utilization  of  feed  in  growth  .         .         .         .         .         .381 

§  3.  The  feed  requirements  for  growth 396 

CHAPTER  XII 

MEAT  PRODUCTION 424 

§  i.  Nature  of  meat  production 424 

§  2.  The  animal  as  a  factor  in  meat  production    .         .         .         .428 

§  3.  Feeding  for  meat  production 444 

§  4.  Influence  of  external  conditions 453 

CHAPTER  XIII 

MILK  PRODUCTION      ..........  459 

§  i.  The  physiology  of  milk  production 459 

§  2.  The  animal  as  a  factor  in  milk  production     ....  47° 

§  3.  The  influence  of  environment  on  milk  production          .         .  478 

§  4.  The  utilization  of  feed  in  milk  production     ....  488 

§  5.  Feeding  for  milk  production  .         .         .     •    .        .        .        -  5°° 


X  CONTENTS 

CHAPTER  XIV 

,  PAGE 

WORK  PRODUCTION .        .531 

§  i.  The  physiology  of  work  production  .  .  .  .  .531 
§  2.  The  efficiency  of  the  body  as  a  motor  .....  544 
§  3.  Feed  requirements  for  work 560 


PART  IV 

THE  FEED   SUPPLY 

CHAPTER  XV 

THE  FEEDING  STUFFS 571 

§  i.  Roughages,  or  coarse  fodders         .         .         .         .        .         .572 

§  2.  Roots,  tubers  and  fruits         .         .         .         .         .        .         .578 

§  3.  The  concentrates 579 

CHAPTER  XVI 

RELATIVE  VALUES  OF  FEEDING  STUFFS 591 

§  i.  Direct  comparisons  of  feeding  stuffs  .  .  .  .  .  591 
§  2.  Relative  values  based  on  composition  and  digestibility  .  597 
§  3.  Conditions  affecting  digestibility  .  .  .  .  .  .601 

CHAPTER  XVII 

THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS         ....  630 

§  i.  General  considerations 630 

§  2.  Production  values  as  regards  energy  —  Net  energy  values    .  634 

§  3.  The  computation  of  net  energy  values  .....  667 

§  4.  Production  values  as  regards  protein 678 

CHAPTER  XVIII 

THE  COMPUTATION  OF  RATIONS         .......    689 

§  i.  Feeding  standards 689 

§  2.  Feed  requirements          .         .        .         .        .         .         .        .691 

§  3.  Method  of  computation         .        .        .        .        .        .        .697 


CONTENTS 


XI 


APPENDIX 

ESTIMATED  PROTEIN  AND  ENERGY  REQUIREMENTS  OF  FARM  ANIMALS 

Table  I.  Maintenance  requirements  of  cattle  and  horses, 
per  day  and  head 

Table  II.  Maintenance  requirements  of  sheep  and  swine,  per 
day  and  head  ....... 

Table  III.  Requirements  for  fattening  with  no  considerable 
growth  —  all  species  —  in  addition  to  the 
maintenance  requirement  .... 

Table  IV.  Requirements  for  growth  with  no  considerable  fat- 
tening ........ 

Table  V.         Requirements  for  milk  production  .... 

Table  VI.        Requirement%for  work  production  by  the  horse 


PAGE 

711 
711 
711 

712 
712 


AVERAGE  DRY  MATTER,  DIGESTIBLE  PROTEIN  AND  NET   ENERGY 

VALUES  OF  FEEDING  STUFFS  PER  100  POUNDS  .  .  .714 
Table  VII.  Values  per  100  pounds  for  ruminants  .  .  .  715 
Table  VIII.  Values  per  100  pounds  for  the  horse  .  .  .721 
Table  IX.  Values  per  100  pounds  for  swine  .  .  .  .722 
Table  X.  Mineral  elements  of  feeding  stuffs  —  per  100 

pounds  of  dry  substance 723 


REFERENCES 

The  full-face  numbers  in  parenthesis  in  the  body  of  the  text  refer  to 
the  numbered  paragraphs  and  not  to  pages. 


ILLUSTRATIONS 


PAGE 


FIG. 

1.  Different  types  of  cells  composing  the  body          •         •         •         •       43 

2.  One  end  of  a  muscle  fiber      ........       50 

3.  Part  of  a  muscle  fiber    .         .         .         .         .         .         .         .         -51 

4.  Fat  cells  in  muscles -52 

5.  Scheme  of  a  fat  cell 5g 

6-8.    Successive  stages  in  the  formation  of  adipose  tissue         .         .       59 
9.    Sheep's  stomach    . go 

10.  Stomach  and  duodenum  of  horse .81 

11.  Stomach  of  hog gx 

12.  Intestines  of  cattle g4 

13.  Ccecum  of  horse g^ 

14.  Section  of  villi IO5 

15.  Steer  in  digestion  stall H3 

16.  Blood  corpuscles I24 

17.  Diagram  of  mammalian  heart         .         .         .         .         .  -125 

18.  Scheme  of  circulation  of  blood      .         .         .         .         .         .         .127 

19.  Relation  of  cells  to  blood  vessels  and  lymphatics          .         .         .     130 

20.  Main  lymphatic  trunks 13! 

21.  Alveoli  of  lung !33 

22.  Section  of  two  alveoli 133 

23.  Diagrammatic  scheme  of  metabolism 182 

24.  Scheme  of  closed-circuit  respiration  apparatus     ....     209 

25.  Original  Regnault-Reiset  apparatus 210 

26.  Regnault-Reiset  apparatus  as  used  by  Zuntz         .         .         .         .     '211 

27.  Scheme  of  Pettenkofer  respiration  apparatus        .         .         .         -213 

28.  Pettenkofer  respiration  apparatus,  explanatory  sketch          .         -213 

29.  The  Mockern  respiration  apparatus      .         .         .         .         .         .214 

30.  Horse  equipped  for  experiments  with  Zuntz  apparatus         .         -215 

31.  Lavoisier's  ice  calorimeter 222 

32.  Section  of  bomb  calorimeter .     224 

33.  The  Zuntz  tread  power  dynamometer   ......     226 

34.  Dulong's  water  calorimeter 237 

35.  The  respiration  calorimeter  at  The  Pennsylvania  State  College  .     238 

36.  Rubner's  calorimeter     .........     239 

37.  The  marbling  of  meat 356 

38.  Rate  of  gain  of  protein  per  1000  pounds  live  weight    .         .         -379 


xiv  ILLUSTRATIONS 

FIG.  PAGE 

39.  Rate  of  gain  of  energy  per  1000  pounds  live  weight     .         .         .  398 

40.  Lobule  of  milk  gland .462 

41.  Alveoli  of  milk  gland 463 

42.  Structure  of  milk  gland           .         .         .         .         .         .         .         .  463 

43.  Partial  section  of  wheat  grain 582 

44.  Partial  section  of  oat  grain    . 584 

45.  Partial  section  of  maize  kernel      .         .         .                  .         .         .  588 


INTRODUCTION 

THE  problems  of  nutrition  concern  the  farmer  both  directly 
and  indirectly  - —  indirectly  because  his  function  in  society  is  to 
furnish  the  materials  for  the  nutrition  of  man  ;  directly,  because 
an  essential  part  of  that  function  consists  in  the  economical 
conversion  of  vegetable  into  animal  products  by  means  of  farm 
animals.  Particularly  is  this  true  regarding  the  inedible  prod- 
ucts of  the  farm.  It  is  a  well-recognized  fact  that  only  the 
smaller  portion  of  the  solar  energy  or  of  the  proteins  which  are 
stored  up  in  the  farmer's  crops  is  directly  available  for  man's 
use.  Even  in  distinctively  food  crops,  such  as  wheat,  for  ex- 
ample, more  than  two-thirds  of  the  energy  which  they  contain 
may  be  unavailable  for  human  nutrition,  while  the  grasses  and 
legumes,  so  important  in  all  systems  of  agriculture,  are  of  no 
direct  value  as  food  for  man.  The  essential  function  of  the 
animal  in  a  permanent  system  of  agriculture  is  the  conversion 
of  as  large  a  proportion  as  possible  of  these  inedible  products 
into  forms  whose  matter  and  energy  can  be  utilized  by  the 
human  body.  It  is  true  that  animal  products  contribute  largely 
to  our  supply  of  clothing  and  also  that,  as  a  motor,  the  work 
animal  plays  an  important  part  in  agriculture  and  industry.  In 
both  respects,  however,  substitution  is  possible  to  a  greater  or 
less  extent.  Vegetable  fibers  may  to  a  degree  replace  animal 
fibers  in  our  textiles,  while  inanimate  motors  seem  destined  to 
fill  an  increasing  role  in  power  production  in  all  its  aspects. 
But  for  the  conversion  of  the  by-products  of  the  farm  and  fac- 
tory into  human  food,  there  is  as  yet  no  suggestion  of  an  agency 
which  can  take  the  place  of  the  animal  body. 

With  the  growth  of  the  non-agricultural  population  it  is  in- 
creasingly important  that  this  function  of  conserving  the  food 
supply  through  the  utilization  of  inedible  soil  products  shall  be 
performed  with  a  maximum  of  efficiency.  This  requires,  on  the 
one  hand,  as  intimate  a  knowledge  as  possible  of  the  funda- 
mental laws  governing  the  nutrition  of  farm  animals,  so  that 


XVI  INTRODUCTION 

the  transformation  may  be  effected  with  the  least  possible  waste, 
and,  on  the  other  hand,  the  ability  so  to  apply  these  laws  as  to 
secure  the  greatest  economic  return,  since  it  must  never  be 
forgotten  that  the  criterion  of  success  in  agriculture  is  not  a 
maximum  production  but  a  maximum  profit.  It  is  with  the 
former  portion  of  this  complex  problem  that  the  present  work 
attempts  primarily  to  deal. 

Without  entering  into  the  controversy  between  the  vitalist 
and  "the  mechanist,  the  nutrition  of  the  animal,  whatever  its 
guiding  principle,  may  be  regarded  as  a  physico-chemical  pro- 
cess, including  the  entire  complex  of  reactions  by  which  the 
crude  materials  of  the  feed  are  converted  into  substances  suited 
to  maintain  the  activities  of  the  body  cells  or  capable  of  being 
built  up  into  living  structures.  In  other  words,  the  study  of 
nutrition  is  a  study  of  the  chemistry  and  physics  of  the  changes 
through  which  the  crude  products  of  the  soil  yield  animal  tissues 
or  secretions  on  the  one  hand  and  excretory  products  on  the 
other. 

The  earlier  investigators  dealt  with  the  food  as  a  supply  of 
matter,  dividing  it  into  inorganic  and  organic  constituents  and 
distinguishing  among  the  latter  between  the  nitrogenous  and 
non-nitrogenous  substances.  In  other  words,  they  studied  the 
problems  of  nutrition  substantially  as  problems  of  biological 
chemistry.  Rubner's  fundamental  investigations  went  far  to 
shift  the  emphasis  to  the  physical  side  of  the  problem.  It  has 
come  to  be  clearly  recognized  that  the  animal  body  is  essen- 
tially a  transformer  of  energy  —  a  mechanism  for  the  conversion 
of  the  chemical  energy  of  its  feed  into  mption  energy  while 
more  or  less  incidentally  a  reserve  of  energy-containing  material 
may  be  stored  up  which  can  be  utilized  for  human  food.  It  is 
this  capacity  of  the  animal  body  to  store  up  in  itself  or  in  its 
secretions  a  part  of  the  matter  and  energy  of  the  feed  it  con- 
sumes which  gives  the  animal  its  economic  significance  as  a 
conserver  of  the  food  supply.  Its  value  in  this  respect  depends 
upon  the  proportion  of  its  feed  which  it  is  able  thus  to  set 
aside  —  i.e.  upon  the  balance  between  the  income  and  outgo 
of  matter  and  of  energy  —  and  it  is  from  this  point  of  view  that 
the  present  volume  undertakes  to  present  the  nutrition  of  farm 
animals.  From  this  standpoint,  the  subject  naturally  falls  into 
four  principal  divisions. 


INTRODUCTION  xvij 

First,  since  nutrition  involves  chemical  changes  by  which 
feed  substances  are  converted  into  body  substances,  there  is 
required  some  knowledge  of  the  chemical  compounds  concerned 
and  of  their  occurrence  and  proportions  in  plants  and  animals. 

Second,  the  conversion  of  feed  substances  into  body  sub- 
stances is  a  function  of  the  living  organism  and  it  becomes 
necessary,  therefore,  to  learn  something  of  the  processes  by 
which  the  body  effects  these  changes  or,  in  other  words,  to 
study  the  physiology  of  nutrition. 

Third,  in  order  to  apply  the  principles  of  the  chemistry  and 
physiology  of  nutrition  to  the  practical  problems  arising  in  the 
feeding  of  farm  animals  it  is  requisite  to  determine  quantita- 
tively the  amounts  of  matter  and  of  energy  which  are  required 
by  different  species  of  animals  for  their  support  and  for  the 
production  of  meat,  milk  or  work. 

Fourth,  to  supply  the  feed  requirements  as  thus  ascertained 
in  the  most  economical  manner  demands  a  knowledge  of  the 
available  feed  resources,  both  as  to  the  nature  and  quantity  of 
nutriment  which  they  contain  and  as  to  the  proportion  of  this 
nutriment  which  can  be  utilized  by  the  body. 

Accordingly,  the  general  subject  of  the  nutrition  of  farm  ani- 
mals is  treated  of  under  four  general  heads,  viz. :  — 

Part  I,      The  Materials  of  Nutrition. 
Part  II,    The  Processes  of  Nutrition. 
Part  III,  The  Feed  Requirements. 
Part  IV,  The  Feed  Supply. 


PART   I 
THE    MATERIALS    OF    NUTRITION 


NUTRITION    OF    FARM 
ANIMALS 

CHAPTER  I 

THE  COMPONENTS  OF   PLANTS  AND  ANIMALS 
§  i.     DRY  MATTER;  ORGANIC  MATTER;   ASH 

1.  Dry    matter.  —  The    material    composing    the    plant    or 
animal  may  be  regarded  as  consisting  of  water  and  dry  matter. 
The  two  are  ordinarily  separated  by  maintaining  the  material 
at  or  above  the  boiling  point  of  water  until  it  ceases  to  lose 
weight.     The  loss  in  weight  is  regarded  as  consisting  solely  of 
water,  while  the  residue  is,  of  course,  the  dry  matter.       , 

2.  Water.  —  Water  is  by  no  means  to  be  regarded   as  an 
accidental  or  incidental  component  of  plants  or  animals.     The 
necessity  for  an  adequate  water  supply  to  living  beings  is  too 
well  known  to  require  mention,  while  very  little  reflection  is 
needed  to  show  that  the  water  is  as  essential  a  part  of  the  organ- 
ism as  any  other  ingredient.     In  the  supporting  tissues  of  the 
plant  or  animal  it  has  a  mechanical  function,  lending  elasticity 
combined  with  strength.     It  acts  as  a  solvent  and  carrier  of 
food  materials  and  waste  products  and  the  osmotic  pressures 
of  the  solutes  are  an  important  factor  in  physiological  processes. 
Finally,  its  action  in  dissociating  electrolytes  appears  to  be 
very  intimately  related  to  the  chemistry  of  living  matter. 

Water  is  usually  abundantly  supplied  to  live  stock.  The 
study  of  animal  nutrition,  therefore,  deals  chiefly  with  the  dry 
matter,  its  supply  and  transformations,  not  because  this  is 
fundamentally  any  more  essential  than  the  water  but  because 
ordinarily  it  is  economically  more  important. 

3 


4  KUtRITIQN  OF  FARM  ANIMALS 

X  Organic  matter.  —  By  the  action  of  oxygen  at  a  high  tem- 
perature, the  dry  matter  of  plants  or  animals  may  be  separated 
into  two  portions,  one  being  converted  into  the  gaseous  state, 
while  the  other  remains  behind  in  the  solid  form.  Following 
the  older  nomenclature,  it  is  customary  to  distinguish  these 
two  portions  as  "  organic  "  and  "  inorganic,"  or  "  ash,"  in- 
gredients. The  terms,  however,  are  to  some  extent  misnomers, 
since  no  such  sharp  distinction  exists  as  was  once  supposed 
between  organic  and  inorganic  compounds.  Organic  matter 
in  the  sense  in  which  the  term  is  commonly  used  may  be  said 
to  be  broadly  equivalent  to  the  carbon  compounds  of  the  organ- 
ism, but  even  this  definition  is  inexact  and  the  same  element 
may  be  volatilized  during  oxidation  or  may  appear  in  the  ash 
according  to  circumstances. 

For  example,  the  element  sulphur  is  an  essential  ingredient 
of  the  proteins.  When  these  are  burned  in  air  part  of  the 
sulphur  escapes  in  the  gaseous  form,  but  a  part  also  combines 
with  any  bases  present  and  appears  in  the  ash  as  sulphates. 
Even  the  element  carbon,  distinctive  of  so-called  organic  matter, 
may  appear  in  part  in  the  ash  of  the  plant  or  animal  in  the  form  of 
carbonates  when  the  bases  of  the  ash  are  in  excess  of  the  acid 
radicles.  These  examples  serve  to  show  that  an  element  may 
be  an  integral  part  of  the  molecules  which  make  up  the  organic 
matter  and  yet  appear  after  incineration  in  the  ash.  Thus  it 
has  recently  been  shown  that  the  phosphorus  of  wheat  bran 
and  other  feeding  stuffs  is  present  chiefly  in  the  form  of  a 
complex  carbon  compound,  yet  when  these  materials  are  burned 
the  phosphorus  appears  in  the  ash  in  the  form  of  phosphates. 

Organic  matter  is  usually  regarded  as  consisting  of  the  ele- 
ments carbon,  hydrogen,  oxygen,  nitrogen  and  sulphur,  phos- 
phorus being  sometimes  added  to  the  list,  but  doubtless  other 
elements  like  potassium,  sodium,  chlorin,  etc.,  also  enter  into 
the  structure  of  the  "  organic  "  molecules. 

4.  Subdivision  of  organic  matter.  —  The  number  of  individ- 
ual organic  compounds  found  in  the  animal  body  or  in  the  plant 
is  very  great.  For  the  present  purpose,  however,  it  is  not 
necessary  to  consider  separately  each  individual  substance  but 
only  the  general  properties  of  the  important  groups  into  which 
they  may  be  classified. 

The  organic  constituents  of  the  body  may  be  subdivided  into 


THE  COMPONENTS  OF  PLANTS  AND  ANIMALS  5 

non-nitrogenous  and  nitrogenous  substances.  Under  the  former 
are  included  the  carbohydrates,  the  fats,  the  organic  acids  and 
various  other  minor  groups.  The  nitrogenous  substances  in- 
clude the  proteins  and  a  variety  of  simpler  nitrogenous  sub- 
stances sometimes  classed  together  as  the  non-proteins.  In  the 
following  sections  these  various  groups  will  be  considered  as 
far  as  is  requisite  for  an  intelligent  study  of  their  behavior  in 
the  animal  body,  it  being  assumed  that  the  reader  has  already 
some  knowledge  of  their  general  properties,  both  chemical  and 
physical. 

5.  Mineral  matter,  or  ash.  — To  what  extent  the  elements 
found  in  the  ash  and  commonly  reckoned  as  the  mineral  ele- 
ments, namely,  potassium,  sodium,  calcium,  magnesium,  iron, 
phosphorus,  sulphur,  chlorin,  silicon,  etc.,  are  actually  present 
in  the  living  plant  or  animal  as  electrolytes  and  to  what  extent 
as  ingredients  of  complex  organic  molecules,  it  is  at  present  im- 
possible to  state  with  any  defmiteness.  In  ordinary  usage  the 
term  ash  is  equivalent  to  the  residue  remaining  after  incineration 
at  as  low  a  temperature  as  possible,  usually  not  exceeding  a 
dull  red  heat. 

The  proportion  of  ash  in  ordinary  feeding  stuffs  varies  con- 
siderably according  to  the  kind  of  plant,  the  portion  of  the  plant 
used  (seeds,  stems,  leaves,  roots,  etc.),  the  maturity  of  the 
plant  and  various  other  conditions.  Wolff  gives  the  following  as 
general  averages  for  the  proportion  of  ash  in  the  dry  matter :  — 


GRAIN 

STRAW 

Cereal  crops  ...              

2% 

5.25% 

3% 

5.00% 

Oil  plants 

4% 

4.50% 

The  proportion  varies  most  in  the  straw  and  least  in  the  grain. 
In  the  animal,  the  presence  of  ash  is  most  evident  in  the  bones. 
About  two-thirds  of  the  dry  matter  of  the  clean  bone  (free  from 
fat)  consists  of  ash.  Ash  is  by  no  means  absent  from  the  soft 
tissues  of  the  body,  however,  of  which  it  forms  an  essential  in- 
gredient. The  proportion  varies  in  different  organs,  but  as 
a  rough  general  average  the  body,  inclusive  of  the  skeleton, 
con  tarns  about  3.5  per  cent  of  ash  in  the  fresh  substance, 


6  NUTRITION  OF  FARM  ANIMALS 

equivalent  to  about  7.1  per  cent  of  the  dry  matter.  The  pro- 
portion of  ash  to  dry  matter  is  greater  in  the  young  than  in  the 
mature  animal  and  greater  in  the  lean  than  in  the  fat  condition. 
The  more  important  elements  found  in  the  ash  are  as  fol- 
lows:— 

Potassium.  —  This  metal  is  indispensable  to  plant  growth  and  is 
found  in  all  parts  of  the  plant,  but  especially  in  the  active,  growing 
parts.  In  the  animal  body  it  is  found  abundantly  in  the  tissues,  such 
as  the  muscles,  glands,  nerves,  etc.,  while  the  fluids  (blood,  plasma, 
lymph,  etc.)  contain  relatively  small  amounts  of  it. 

Sodium.  —  Unlike  potassium,  sodium  is  not  indispensable  to  plant 
growth,  although  it  apparently  is  useful  to  the  plant  under  some  con- 
ditions. It  is  found  especially  in  the  stems  and  leaves  of  plants, 
although  not  so  abundantly  as  potassium.  Seeds  contain  but  little 
of  it.  In  the  animal  body  it  is  especially  abundant  in  the  fluids, 
which,  as  just  noted,  contain  relatively  little  potassium. 

Calcium.  —  Like  potassium,  calcium  is  necessary  for  the  growth 
of  plants.  It  is  found  especially  in  the  leaves  and  stems  of  plants 
and  to  a  much  less  extent  in  the  seeds.  It  appears  to  be  equally 
essential  to  the  animal  and  is  found  in  all  parts  and  organs  of  the  body. 
Its  most  striking  use,  however,  is  in  the  formation  of  the  skeleton,  the 
mineral  portion  of  which  (81)  consists  chiefly  of  calcium  phosphate 
and  carbonate.  Both  these  compounds  being  scarcely  at  all  soluble 
in  water,  they  are  well  adapted  to  form  the  framework  of  the  body. 
In  the  skeletons  of  the  higher  animals  calcium  phosphate  is  the  chief 
mineral  ingredient,  while  in  the  lower  animals  like  shellfish  and 
Crustacea,  the  shell,  which  corresponds  to  the  bones  of  domestic  ani- 
mals, contains  chiefly  calcium  carbonate. 

Magnesium.  —  Magnesium  is  also  one  of  the  elements  essential 
for  plant  growth.  It  is  found  throughout  the  plant  in  smaller  amounts 
than  calcium,  but  is  more  abundant  than  the  latter  in  the  seeds  and 
seems  to  aid  in  seed  formation.  In  the  animal  body,  magnesium 
usually  accompanies  calcium,  but  in  much  smaller  amounts. 

Iron.  —  A  small  amount  of  iron  is  required  by  the  higher  plants 
for  the  formation  of  the  green  coloring  matter  (chlorophyl)  by  means 
of  which  they  assimilate  the  carbon  dioxid  of  the  air.  In  the  ani- 
mal, iron  in  small  quantity  is  necessary  for  the  formation  of  the  red 
coloring  matter  (haemoglobin)  of  the  blood  which  is  the  agent  for 
conveying  the  oxygen  of  the  air  to  the  tissues.  While,  therefore,  but 
a  very  small  amount  of  iron  is  required  by  either  plants  or  animals,1 
it  is  nevertheless  essential  to  the  most  fundamental  processes  of  life. 

1  It  is  estimated  that  the  blood  of  an  adult  man  contains  about  3  grams  of  iron. 


THE  COMPONENTS   OF  PLANTS  AND   ANIMALS  7 

Phosphorus.  —  Phosphorus  is  another  of  the  elements  essential  to 
plant  growth,  its  chief  function  seeming  to  be  to  aid  in  the  produc- 
tion and  transportation  of  the  proteins.  It  is  found  in  all  parts  of 
the  plant  but  accumulates  especially  in  the  seeds. 

Plants  may  contain  more  or  less  phosphorus  in  the  form  of  phos- 
phates, especially  in  their  vegetative  organs.  Even  in  the  latter, 
however,  a  considerable  share  of  it  is  in  "organic"  combination,  while 
in  the  seeds  but  very  small  amounts  of  " inorganic"  phosphorus  are 
found.  The  " organic."  phosphorus  of  plants  is  contained  chiefly  in 
three  classes  of  compounds,  viz.,  the  phosphatids  (37,  38),  or  so- 
called  phosphorized  fats,  the  nucleo-  and  phospho-proteins  (52,  55), 
and  phytin,  the  latter  being  the  chief  phosphorus  compound  of  seeds. 
Phytin  is  a  compound  of  phosphoric  acid  and  inosit  and  may  be  split 
up  into  these  constituents  by  hydrolysis  and  also  by  an  enzym  found 
in  seeds. 

In  the  animal,  the  great  store  of  phosphorus  is  found  in  the  skele- 
ton, where  it  exists,  as  already  stated,  chiefly  in  the  form  of  calcium 
phosphate.  It  is  also  found  somewhat  abundantly  in  the  soft  tissues 
of  the  body,  of  which  it  is  an  essential  ingredient.  Here  it  seems  to 
exist  largely  in  "organic"  combination  in  the  phosphatids  and  the 
nucleo-  and  phospho-proteins. 

Sulphur.  —  Sulphur  is  taken  up  by  the  roots  of  the  plant  in  the 
form  of  sulphates,  and  when  plant  or  animal  substances  are  burned, 
more  or  less  of  the  sulphur  which  they  contain  is  found  as  sulphates 
in  the  ash.  For  these  reasons,  sulphur  has  been  commonly  regarded 
as  one  of  the  ash  ingredients  of  plants  and  animals.  As  a  matter  of 
fact,  however,  as  already  pointed  out,  it  is  usually  as  truly  an  "or- 
ganic" ingredient  as  nitrogen  or  carbon.  In  particular,  it  is  one  of 
the  elements  of  which  the  proteins  are  composed,  and  seems  to  exist 
in  the  plant  and  animal  chiefly  in  this  form. 

Chlorin.  —  Chlorin  is  found  in  plants  associated  with  sodium. 
It  does  not  seem  to  be  necessary  to  plant  life.  In  the  animal  it  is  an 
essential  element  in  the  gastric  juice. 

Small  amounts  of  fluorine  and  traces  of  iodin  and  of  manganese 
and  other  catalysts  also  occur,  but  their  specific  functions  are  obscure 
except  that  fluorin  is  an  ingredient  of  the  enamel  of  the  teeth. 


§  2.  THE  CARBOHYDRATES 

6.  Occurrence.  —  Although  substances  belonging  to  this 
group  of  compounds  are  found  in  the  bodies  of  animals,  they 
are  especially  characteristic  of  plants.  Starch,  one  of  the  most 
familiar  of  them,  is  the  first  visible  product  of  the  assimilation 


8  NUTRITION  OF  FARM  ANIMALS 

of  carbon  dioxid  by  chlorophyl-bearing  plants,  and  the  great 
mass  of  vegetable  tissue  is  composed  either  of  carbohydrates  or 
of  their  nearly  related  derivatives. 

The  more  common  carbohydrates  have  been  known  for  a  long 
time.  Starch  is  familiar  to  us  in  the  mealy  portion  of  grains  and 
in  certain  tubers,  and  cellulose  in  cotton  and  linen  and,  in  im- 
pure forms,  in  the  woody  fiber  of  plants.  Of  the  sugars,  cane 
sugar  has  been  known  since  almost  prehistoric  times,  while  the 
presence  of  this  and  other  sugars  in  plant  juices,  in  sweet  fruits, 
honey,  etc.,  is  a  familiar  fact.  The  more  common  sugars  were 
separated  and  identified  quite  early  in  the  history  of  chemistry. 

7.  Classification.  —  The    carbohydrates    contain    hydrogen 
and  oxygen  in  exactly  the  proportions  to  form  water,  and  their 
name  is  derived  from   this  fact,   although  compounds   exist 
which  contain  two  atoms  of  hydrogen  to  one  of  oxygen  and 
yet  are  not  carbohydrates,  such,  for  example,  as  acetic  acid, 
C2H4O2.     The  simplest  of  the  carbohydrates  are  the  simple 
sugars,  more  exactly  designated  as  the  monosaccharids.     By 
polymerization,  with  elimination  of  water,  the  monosaccharids 
yield  more  complex  carbohydrates  which  are  conveniently  classi- 
fied as  di-,  tri-,  and  polysaccharids. 

Monosaccharids,  or  simple  sugars 

8.  Composition.  —  The  monosaccharids  may  be  represented 
by  the  general  formula  Cn  H2n  On.     Substances  having  this  gen- 
eral formula  are  known  whose  molecules  contain  from  one  to 
nine  carbon  atoms  and  which,  from  a  chemical  point  of  view, 
may  be  called  carbohydrates.     The  simplest  of  these  is  formal- 
dehyde, CH2O,  which  is  believed  by  many  to  be  the  first  step  in 
the  synthesis  of  carbohydrates  by  the  green  plant.     Only  the 
CG  and  C&  compounds,  however,  known  respectively  as  the 
hexose  and  pentose  carbohydrates,  are  of  importance  in  their 
relations  to  nutrition. 

9.  Hexoses.  —  The  most  important  hexose  monosaccharids 
are  dextrose,  levulose,  galactose  and  mannose. 

Dextrose,  ^-glucose,  or  grape  sugar,  is  generally  regarded  as 
an  aldose  of  the  hexatomic  alcohol  sorbite. ' 

Sorbite :   CH2OH-  (CH  -  OH)4-  CH2OH 
Dextrose :   CH2OH-  (CH  •  OH)4-  CHO 


THE  COMPONENTS  OF  PLANTS  AND  ANIMALS  9 

It  occurs  almost  universally  in  the  juices  of  plants  along  with 
levulose  and  cane  sugar,  and  is  found  also  in  small  amounts  in 
the  blood  of  mammals.  Sixteen  isomers  of  this  compound 
are  possible,  twelve  of  which  are  known. 

Galactose  and  mannose  are  isomers  of  dextrose,  occurring  in 
nature  only  in  combination  as  di-  or  polysaccharids. 

Levulose,  or  fruit  sugar,  is  a  ketose  of  sorbite,  having  the 
formula  CH2OH-(CH  •  OH)3-CO-CH2OH,  eight  isomers 
being  theoretically  possible.  It  occurs  mixed  with  dextrose  in 
plant  juices  and  in  honey. 

The  hexose  monosaccharids  are  all  soluble  in  water  and 
readily  diffusible  and  have  a  more  or  less  sweet  taste.  All 
those  found  in  nature  are  optically  active,  rotating  the  plane 
of  polarized  light.  Thus  dextrose,  as  its  name  implies,  has  a 
right-handed  rotation  and  levulose  a  left-handed  rotation. 
They  reduce  an  alkaline  solution  of  metallic  salts,  especially  of 
copper,  and  this  fact  is  utilized  both  as  a  qualitative  test  for 
them  and  as  a  means  of  quantitative  determination.  They  are 
fermented  by  yeast,  yielding  as  the  chief  products  ethyl  alcohol 
and  carbon  dioxid. 

10.  Pentoses.  —  The  pentoses  are  simple  sugars,  correspond- 
ing to  the  hexoses  but  having  the  general  formula  C5Hi0O5. 
Those  occurring  in  nature  are  aldoses.  Like  the  hexoses,  they 
reduce  metallic  oxids,  but  unlike  them  they  are  not  ferment- 
able by  yeast. 

Arabinose.  —  By  the  hydrolysis  of  gum-arabic  or  cherry  gum, 
there  is  produced  dextro-rotatory  arabinose  (/-arabinose).  Levo- 
rotatory  arabinose  (^-arabinose)  has  been  prepared  artificially.  The 
inactive  or  racemic  form  (£-arabinose)  has  been  found  in  human 
urine  in  small  amounts. 

Xylose.  —  By  the  hydrolysis  of  wood  gum  there  is  produced  a 
dextro-rotatory  pentose  known  as  /-xylose.  The  levo-rotatory  form 
of  the  same  sugar  (d-xylose)  is  obtained  in  the  hydrolysis  of  certain 
nucleo-proteins,  the  pentose  group  seeming  to  be  a  constituent  of 
the  molecule  of  those  compounds. 

Rhamnose  is  a  derivative  of  the  pentose  sugars  in  which  an  atom 
of  hydrogen  has  been  replaced  by  methyl.  It  occurs  somewhat 
widely  in  the  vegetable  kingdom. 


10  NUTRITION   OF  FARM  ANIMALS 

Glucosids 

11.  The  monosaccharids  not  only  occur  in  the  free  state  but 
also  in  combination  with  a  great  variety  of  substances  in  the 
so-called  glucosids.     The  glucosids  readily  undergo  hydrolytic 
cleavage  into  their  two  (or  more)  constituents,  either  by  the 
action  of  chemical  reagents  or  of   enzyms.     For  example,  the 
amygdalin  of  the  bitter  almond  yields  two  molecules  of  dextrose, 
one  of  benzaldehyd  and  one  of  hydrocyanic  acid,  and  cerebron, 
a  constituent  of  the  brain,  splits  up  into  cerebronic  acid,  sphin- 
gosin  and  galactose.     Among  other  more  or  less  familiar  glucosids 
may  be  mentioned  salicin,  saponin,  phloridzin  and  digitalin. 

Disaccharids 

12.  The  hexose  group.  —  The  disaccharids  may  be  regarded 
as  polymers  or  anhydrids  of  the  monosaccharids,  formed  by  the 
union  of  two  molecules  of  the  latter  with  the  elimination  of  one 
molecule  of  water.     The  only  disaccharids  at  present  known  be- 
long to  the  hexose  group  and  their  formation  may  be  repre- 
sented by  the  equation  C6Hi2O6  +  C6Hi2O6  =  Ci2H22On  +  H2O. 
From  another  point  of  view  they  are  termed  by  some  writers 
glucosids  of  the  monosaccharids. 

Sucrose.  —  Sucrose,  or  cane  sugar,  has  probably  been  longest 
known  of  the  more  familiar  carbohydrates.  It  is  found  in  the 
juices  of  the  sugar  cane  and  sorghum,  in  the  sugar  beet  and  in 
the  sap  of  the  maple,  all  of  which  are  utilized  as  commercial 
sources  of  sugar.  In  smaller  amounts  it  is  present  in  a  large 
number  of  plants. 

By  the  action  of  heat,  aided  by  a  dilute  acid  or  alkali,  or  by 
the  action  of  certain  enzyms,  notably  the  invertase  of  yeast, 
the  reverse  of  the  general  reaction  for  the  formation  of  the 
disaccharids  may  be  brought  about,  one  molecule  of  sucrose 
combining  with  one  molecule  of  water  to  yield  one  molecule 
each  of  dextrose  and  levulose. 


Ci2H22Oii  +  H2O  =  C6Hi206  +  C6Hi2O6 

Sucrose  rotates  the  plane  of  polarized  light  to  the  right, 
while,  owing  to  the  fact  that  the  rotatory  power  of  levulose  is 
greater  than  that  of  dextrose,  the  mixture  of  equal  parts  of  the 
two  which  is  formed  in  the  foregoing  reaction  rotates  to  the 


THE   COMPONENTS   OF  PLANTS  AND   ANIMALS          II 

left.  On  account  of  this  fact,  this  breaking  up  of  cane  sugar 
has  been  called  inversion  and  the  use  of  this  term  has  been 
extended  to  designate  in  general  the  hydrolytic  cleavage  of  di- 
saccharids  into  their  constituent  monosaccharids. 

Lactose.  —  Lactose,  or  milk  sugar,  is  a  characteristic  ingredi- 
ent of  the  milk  of  mammals.  Like  sucrose,  it  may  be  broken 
up,  with  the  addition  of  one  molecule  of  water,  into  two  mole- 
cules of  monosaccharids,  in  this  case  dextrose  and  galactose. 
It  is  less  soluble  than  sucrose  and  therefore  less  sweet  to  the 
taste,  having  a  gritty  feel  in  the  mouth.  It  is  not  found  in 
plants. 

Maltose.  —  By  the  action  of  certain  ferments  upon  starch 
during  the  germination  of  seeds  and  also  in  the  digestive  tract 
of  animals,  a  disaccharid  known  as  maltose  is  produced.  It  is 
therefore  present  abundantly  in  malt,  whence  its  name.  This 
sugar  when  hydrolyzed  yields  two  molecules  of  dextrose. 

13.  General  properties.  —  The  disaccharids  are  crystalline, 
soluble  in  water  and  optically  active.     Sucrose  does  not  reduce 
an  alkaline  copper  solution,  but  lactose  and  maltose  do.     The 
disaccharids  are  not  fermentable.     Any  cases  in  which  they  are 
apparently  fermented  are  found  to  be  preceded  by  some  action 
which  inverts  or  breaks  up  the  disaccharids  into  their  con- 
stituent monosaccharids. 

Trisaccharids 

14.  By  the  union  of  three  molecules  of  CeH^Oe  with  the 
elimination  of  two  molecules  of  water,  there  may  be  formed 
the    compound    CigH-BOie,  called    a  trisaccharid.     One    such, 
known  as  raffinose,  is  present  in  the  sugar  beet,  the  cotton  seed, 
in  barley  and  in  wheat.     Upon  hydrolysis  it  yields  one  mole- 
cule each  of  dextrose,  levulose  and  galactose. 


Polysaccharids 

15.  Chemical  structure.  —  The  polysaccharids,  like  the  di- 
saccharids, are  anhydrids,  but  are  formed  by  the  combination  of 
many  molecules  of  the  monosaccharids  and  have  a  correspond- 
ingly high  molecular  weight.  The  general  formula  of  the  hexose 
polysaccharids  is  (C6H10O5)n,  the  value  of  n  doubtless  varying 


12  NUTRITION  OF  FARM  ANIMALS 

through  a  wide  range,  but  the  molecular  weights  of  the  in- 
dividual polysaccharids  have  not  been  finally  determined. 

The  polysaccharids  are  tasteless  and  usually  amorphous  sub- 
stances which,  with  the  exception  of  cellulose,  are  more  or  less 
soluble  in  water.  They  are  optically  active  but  in  general  are 
not  diffusible  through  membranes.  They  are  hydrolyzed  easily, 
especially  by  the  action  of  heat  and  acids  and  by  enzyms,  yield- 
ing ultimately  monosaccharids. 

In  addition  to  their  common  names,  they  are  designated  by 
terms  derived  from  the  monosaccharids  out  of  which  they  are 
built  up.  Thus  starch,  which  is  an  anhydrid  of  dextrose  and 
yields  only  this  sugar  upon  hydrolysis,  is  a  dextran.  Similarly, 
there  are  levulans,  galactans,  mannans,  arabans,  xylans,  etc., 
yielding  the  corresponding  sugars  when  hydrolyzed.  In  the 
same  manner,  it  is  customary  to  distinguish  between  the 
hexosans,  derived  from  the  hexoses,  and  the  pentosans,  the 
anhydrids  of  the  pentoses. 

16.  The  hexosans.  —  This  group  of  carbohydrates  includes 
those  which  are  most  abundant  in  the  vegetable  kingdom  and 
of  the  greatest  significance  as  sources  of  nutriment  for  man  and 
animals,  viz.,  starch,  the  dextrins  and  gums,  and  cellulose  and 
its  various  derivatives.     It  will  be  convenient  to  consider  the 
more  important  hexosans  somewhat  in  the  order  of  their  re- 
sistance to  solvents. 

17.  Cellulose.  —  Cellulose  constitutes  the  basis  of  the  cell 
walls  of  plants  and  is  also  found  in  certain  lower  animals  (tuni- 
cates).     Clean  cotton  consists  of  nearly  pure  cellulose,  each 
fiber  being  a  single  cell  from  which  the  contents  (protoplasm) 
have  nearly  disappeared.     Linen  and  the  best  qualities  of  paper 
are   other   examples   of  nearly  pure   cellulose.     A   crystalline 
form  has  also  been  described. 

Cellulose  is  insoluble  in  water  and  comparatively  resistant 
to  reagents  in  general.  Plants,  however,  contain  enzyms 
(cytases)  which  are  able  to  bring  it  into  solution  in  the  processes 
of  plant  growth,  and  apparently  these  enzyms  play  some  part 
in  its  digestion  by  animals.  It  is  also  attacked  and  dissolved 
by  some  species  of  bacteria.  Concentrated  sulphuric  acid  dis- 
solves it,  and  the  solution,  on  dilution  and  boiling,  undergoes 
hydrolysis,  yielding  dextrose.  Cellulose  is  therefore  a  dextran. 
Its  molecular  weight  is  unknown. 


THE   COMPONENTS  OF  PLANTS  AND   ANIMALS         13 

18.  Hemicelluloses.  —  These  polysaccharids  differ  from  true 
cellulose  in  being  hydrolyzed  by  comparatively  short  boiling 
with  dilute  acids  and  further  in  the  fact  that  the  hydrolysis, 
instead  of  yielding  only  dextrose,  as  in  the  case  of  cellulose, 
produces  a  variety  of  both  hexose  and  pentose  sugars,  the 
former  including  galactose,  mannose  and  levulose,  as  well  as 
dextrose,  and  the  latter  arabinose  and  xylose.     The  hemicellu- 
loses  must  be  regarded,  therefore,  as  containing  both  hexosans 
and  pentosans,  but  whether  in  mixture  or  chemical  union  is 
uncertain.     While  true  cellulose  constitutes  the  framework  of 
the  plant,  the  hemicelluloses  serve  to  a  greater  or  less  extent  as 
reserve  material.     In  the  conventional  method  of  feeding  stuffs 
analysis,  the  hemicelluloses  are  found  both  in  the  "  crude  fiber  " 
(109)  and  in  the  "  nitrogen-free  extract  "  (110). 

19.  Lignin.  —  In  the  young  plant,  the  cell  walls  consist  of 
nearly  pure  cellulose.     With  advancing  maturity  they  become 
thickened,  not  only  by  the  formation  of  additional  cellulose  and 
of  hemicelluloses  but  by  the  deposition  of  numerous  "  incrusting 
substances,"  the  most  important  group  of  which  has  received 
the  collective  name  of  lignin.     These  substances  contain  a  con- 
siderably higher  percentage  of  carbon  than  cellulose  (54  to  60 
per  cent)  and  may  be  separated  from  the  latter  by  oxidizing 
agents.     The  substances  of  the  lignin  group  contain  methoxyl 
(— O-  CH3)  and  ethoxyl  (— O  •  C2H5)  groups  in  considerable 
amount,  and  by  some  are  regarded  as  substituted  celluloses. 

20.  Crude  fiber.  —  The  so-called   "  crude  fiber  "   (109)  of 
plants  contains  most  of  the  cellulose  and  lignin  of  the  cell  walls 
and  in  addition  a  third  group  —  the  cutin  group1  —  whose  per- 
centage of  carbon  is  still  higher  (60-75  Per  cent).     Cutin  appears 
to  be  indigestible. 

21.  Starch.  —  Starch  is  one  of  the  most  common  and  impor- 
tant of  the  vegetable  carbohydrates.     In  the  growth  of  plants, 
starch  is  formed  in  the  green  leaves  by  the  aid  of  light,  and  is 
the  first  visible  product  of  assimilation.     In  the  mature  plant, 
it  is  stored  up  in  large  quantities  in  the  seed  or  in  the  tuber  to 
supply  the  needs  of  the  new  plant.     Hence  the  common  grains, 
corn,  wheat,  oats,  barley,  etc.,  as  well  as  potatoes,  are  rich  in 
starch  and  form  commercial  sources  of  it.     The  seeds  of  most 
legumes  contain  it  in  less  amounts  but  still  abundantly.     In 

1  Compare  Konig:  Landw.  Vers.  Stat.,  65  (1907),  55. 


14  NUTRITION   OF   FARM   ANIMALS 

the  oil  seeds  it  is  replaced  by  oil.  It  is  not  found  in  the  animal 
body. 

Starch  occurs  in  plants  in  the  form  of  microscopic  granules, 
which  have  a  peculiar  form  for  each  species,  so  that  we  may  speak 
of  the  starches  rather  than  of  starch.  These  grains  consist  of 
a  surrounding  envelope  consisting  of  a  variety  of  cellulose  in- 
closing a  more  soluble  substance  or  substances  known  as  granu- 
lose.  When  treated  with  much  hot  water  the  starch  grain  swells 
and  bursts  the  envelope  and  the  enclosed  granulose  dissolves, 
probably  after  undergoing  more  or  less  hydration. 

Starch  may  be  hydrolyzed  readily  by  dilute  acids  or  alkalies 
or  by  heat.  The  final  product  of  its  hydrolysis  is  dextrose, 
which  in  an  impure  form  constitutes  commercial  glucose  or 
starch  sugar.  Starch  is  therefore  a  dextran.  As  already  noted, 
certain  enzyms,  notably  those  formed  in  germinating  seeds 
and  others  secreted  in  the  digestive  tract  of  animals,  act  upon 
starch  readily  with  the  production  of  maltose.  Starch  is  also 
acted  upon  by  some  species  of  bacteria  with  the  formation  of 
lactic,  butyric  and  other  acids,  methan  and  in  some  cases  hy- 
drogen. 

22.  Galactans.  —  Galactans  occur  more  particularly  in  le- 
guminous plants,  other  feeding  stuffs  being  comparatively  free 
from  them. 

23.  Inulin.  —  The  roots  of  the  artichoke,  dahlia,  dandelion, 
chicory  and  other  composites  contain  instead  of  starch  a  quite 
similar  carbohydrate,  inulin,  which  on  hydrolysis  yields  levulose 
instead  of  dextrose,  i.e.,  it  is  a  levulan, 

24.  The  dextrins.  —  In  the  hydrolysis  of  starch  a  series  of 
ill-defined,  intermediate  compounds  is  produced,   collectively 
called  dextrins.     Commercial  dextrin  is  made  by  heating  moist 
starch  to  about  235°  Fahrenheit.     It  is  likewise  produced  in  the 
cooking  of  starchy  materials,  the  brown  crust  of  bread,   for 
example,  consisting  largely  of  dextrin.     Various  dextrins  have 
been    separated    and   described,   but    it    seems    questionable 
whether  the  investigators  have  worked  with  definite  chemical 
individuals.     For  the  present,  it  seems  wiser  to  speak  collec- 
tively of  the  dextrins  as  intermediate  products  between  starch 
and  the  simpler  di-  and  mono-saccharids. 

25.  Glycogen.  —  In  the  liver  and  muscles  of  animals,  and  to 
a  less  degree  in  other  parts  of  the  body,  there  is  found  in  rather 


THE  COMPONENTS   OF  PLANTS  AND   ANIMALS          15 

small  amounts  a  carbohydrate  called  glycogen.  Glycogen  has 
the  same  percentage  composition  as  starch  and  has  sometimes 
been  called  animal  starch,  although  improperly,  since  its  proper- 
ties are  quite  different  from  those  of  starch.  It  has  important 
functions  in  the  animal,  as  will  appear  later.  It  is  not  found  in 
the  plant.  It  is  readily  soluble  in  water,  yielding  an  opalescent 
solution.  The  empirical  formula  of  glycogen  is  the  same  as 
that  of  starch.  When  hydrolyzed  it  yields  only  dextrose,  and 
is  therefore  a  dextran. 

26.  The  gums.  —  Familiar  examples  of   this  class  of   sub- 
stances are  gum  arabic  and  the  gums  of  the  cherry,  peach  and 
plum.     The  mucilage  of  flax  seed  closely  resembles  the  gums, 
and  other  seeds  also  contain  gum-like  "bodies.     Upon  hydrolysis, 
the  gums  yield  hexoses,  especially  galactose,  showing  that  they 
contain  galactans.     In  addition  to  hexoses,  however,  they  yield 
sugars  belonging  to  the  pentose  group. 

27.  The  pentosans.  —  The  pentosans   may  be  regarded  as 
polymers  or  anhydrids  of  the  pentoses,  corresponding  in  this 
respect   to   the   polysaccharids   of   the   hexose   group.     Their 
general  formula  is  (CsHgC^),,,  but  their  molecular  structure  is 
unknown. 

Araban.  —  This  is  a  constituent  of  gum  arabic  and  other 
gums,  as  shown  by  the  fact  that  these  gums,  as  already  noted 
(10),  yield  /-arabinose  when  hydrolyzed. 

Xylan.  —  This  compound  is  also  known  as  wood  gum.  It 
can  be  extracted  from  various  woods,  from  the  cob  of  maize 
and  from  various  other  vegetable  materials  by  the  action  of 
dilute  alkalies,  and  yields  /-xylose  when  hydrolyzed.  In  the 
plant,  araban  and  xylan  appear  to  be  in  a  more  or  less  close 
chemical  combination  with  hexosans,  especially  in  the  cell  walls 
of  the  more  mature  plant,  constituting  the  so-called  hemi- 
celluloses  (18). 

Pectins.  —  Most  ripe  fruits,  as  well  as  the  flesh  of  beets, 
turnips  and  similar  roots,  contain  a  group  of  substances  called 
the  pectin  group.  As  they  exist  in  the  roots  or  fruits  they  are 
insoluble  in  water,  but  by  cooking  they  are  converted  into  sub- 
stances which  form  the  basis  of  fruit  jellies.  On  hydrolysis 
they  yield  pentoses,  chiefly  arabinose. 


1 6  NUTRITION  OF  FARM  ANIMALS 

§  3.   FATS  AND  RELATED  BODIES  —  THE  LIPOIDS 

28.  Classification.  —  Under  the  rather  vague  term  "  lipoids," 
or  fat-like  substances,  there  are  included,  besides  true  fats,  a 
large  number  of  chemical  individuals  of  varied  and  complex 
molecular  structure.     Chemically,  these  substances  (with  the 
exception  of  the  cholesterins)  are  characterized  by  containing 
radicles  of  the  so-called  fatty  acids,  principally  the  higher  ones 
of  the  series.     Physically,  the  lipoids  have  been  defined,  prin- 
cipally from  the  standpoint  of  the  physiological  chemist,  as 
substances  which  are  soluble  in  organic  solvents,  such  as  ether, 
alcohol,  chloroform  or  benzol.     This  latter  definition,  however, 
includes  substances,  such  as  the  cholesterins,  which  would  be 
excluded  by  the  chemical  definition  just  given.     For  the  present 
purpose,  the  principal  lipoids  may  be  conveniently  grouped  under 
five  heads :   (i)  fats,  (2)  waxes,  (3)  cholesterins,  (4)  phosphatids 
or  phospholipins,  (5)  cerebrosids  or  galactolipins. 

The  Fats 

29.  Occurrence.  —  It  is  a  familiar  fact  that  the  bodies  of 
animals  contain  a  not  inconsiderable  amount  of  fat,  the  per- 
centage seldom  falling  below  six  in  the  very  lean  animal  while  it 
may  rise  as  high  as  forty  in  the  very  fat  animal.     The  fat  is 
the  reserve  material  of  the  body  and  is  contained  in  what  is 
called  adipose  tissue  (94) ,  consisting  of  cells  of  connective  tissue 
more  or  less  filled  with  fat.     Larger  or  smaller  amounts  of  adi- 
pose tissue  are  found  in  all  parts  of  the  body  but  especially  in 
the  subcutaneous  tissues,  the  tissues  surrounding  the  intestines, 
and,  particularly  in  fat  animals,  in  the  muscles. 

In  plants,  fats  are  usually  less  abundant.  They  occur  in 
all  parts  of  the  plant  but  are  especially  stored  up  in  the  seeds, 
where  they  serve  as  reserve  material  which  is  metabolized 
during  germination.  Some  seeds,  like  those  of  cotton,  flax 
and  rape,  contain  fat  so  abundantly  that  they  are  commercial 
sources  of  oil.  In  the  plant,  the  fat  is  not  deposited  in  special 
tissues  but  is  usually  distributed  through  the  protoplasm  of 
the  cell.  Both  animal  and  vegetable  fats  are  mixtures  of 
various  simple  fats,  often  containing  also  small  amounts  of 
free  fatty  acids. 


THE  COMPONENTS  OF  PLANTS  AND   ANIMALS         17 

30.  Molecular  structure.  —  The  simple  neutral  fats  are  tri- 
glycerids,  that  is,  they  are  esters  of  the  triatomic  alcohol 
glycerol  with  monobasic  fatty  acids,  the  hydrogen  atoms  of 
the  three  hydroxyls  being  replaced  by  the  acid  radicles.  Their 
general  formula  is  as  follows,  RI,  R2  and  R3  representing  the 
acid  radicles,  which  may  or  may  not  be  the  same  :  — 

Glycerol         CH2  -  OH  —  CH  .  OH  —  CH2  .  OH 
Neutral  fat  CH2  .  ORi  —  CH  •  OR2  —  CH2  .  OR3 


The  fatty  acids  may  be  divided  into  the  saturated  and  the 
unsaturated.  The  saturated  fatty  acids  have  the  general  for- 
mula CraH2nO2  and  are  the  normal  acids  of  the  aliphatic  series, 
the  two  lower  members  of  which  are  familiar  as  formic  and 
acetic  acids.  The  general  formula  of  these  acids  is  as  follows, 
each  carbon  atom  being  united  to  the  adjacent  ones  by  a  single 
bond. 

CH3-(CH2)n  -COOH 

The  two  principal  saturated  acids  contained  in  the  animal  fats 
are  stearic  acid,  Ci8H36O2,  and  palmitic  acid,  CieH32O2.  Besides 
these  two,  however,  others  are  also  found  in  small  amounts. 
In  butter  fat,  especially,  several  of  the  lower  acids  of  the  series 
are  present,  the  principal  ones  being  butyric,  C4H8O2,  caproic, 
C6Hi2O2,  caprylic,  C8Hi6O2,  capric,  Ci0H2oO2,  lauric,  Ci2H24O2 
and  myristic,  Ci4H28O2.  In  the  body  fats  there  have  been 
found  also  higher  acids  of  the  same  series,  particularly  arachnic 
acid,  C2oH4oO2. 

The  unsaturated  fatty  acids  differ  from  the  saturated  acids 
in  containing  two  or  more  carbon  atoms  united  by  two  bonds 
instead  of  one  and  consequently  in  containing  less  hydrogen 
than  the  saturated  acids.  Of  the  unsaturated  acids,  the  most 
abundant  in  animal  fats  is  oleic  acid,  having  the  formula 

CH3-(CH2)7-CH  =  CH-(CH2)7-COOH 

The  eruic  acid  of  rape  oil  also  belongs  to  this  series,  and  the 
linoleic  acid,  Ci8H32O2,  of  linseed  oil  and  other  drying  oils  belongs 
to  a  related  series  of  unsaturated  acids  of  the  general  formula 
CnH2n_4O2  with  two  double  unions  of  carbon  atoms. 

It  is  a  noteworthy  fact  that  nearly  all  the  fatty  acids  occurring 
in  the  animal  body  contain  an  even  number  of  carbon  atoms. 


1 8  NUTRITION  OF  FARM  ANIMALS 

31.  Chemical  reactions.  —  Of  the  chemical  reactions  of  the 
fats,  the  one  of  most  importance  physiologically  is  that  known 
as  saponification,  or  more  strictly  as  hydrolysis.     It  consists  of 
a  cleavage  and  hydration  of  the  molecule,  yielding  glycerol  and 
fatty  acids.     The  most  familiar  instance  of  this  reaction  is  in 
the  process  of  soap  making.     For  example,  if  tri-stearin  is  acted 
upon  by  potassium  hydrate  the  final  result  is  as  represented 
by  the  following  equation  :  — 

C3H5(C18H3502)3  +  (KOH)3  =  (KC18H3502)3  +  C3H8O3 

Tristearin      Potassium  hydrate  Potassium  tristearate      Glycerol 

In  this  reaction,  the  alkali  salt  of  the  fatty  acid,  that  is,  a 
soap,  is  obtained.  By  the  action  of  water  at  temperatures  con- 
siderably above  100°  C.,  essentially  the  same  result  is  reached 
except  that  the  free  acid  is  obtained  instead  of  the  salt.  The 
same  decomposition  may  also  be  effected  by  means  of  acids, 
which  probably  act  as  catalyzers. 

Of  most  importance  physiologically  is  the  hydrolysis  of  fat  by 
means  of  enzyms.  Such  enzyms  are  produced  by  certain  plants 
and  are  also  found  in  various  digestive  juices,  notably  in  the 
secretion  of  the  pancreas.  These  enzyms  have  received  the 
general  name  of  Upases.  The  hydrolysis  of  fats  by  enzyms 
appears  to  be  a  reversible  reaction,  at  least  with  the  glycerids 
of  low  molecular  weight.  In  other  words,  the  same  enzym 
may  effect  the  cleavage  of  a  glycerid  or  the  combination  of 
glycerol  and  the  fatty  acid,  the  reaction  in  either  case  reaching 
an  equilibrium  at  a  certain  stage.. 

32.  Physical    properties.  —  Certain   general    properties    are 
common  to  all  the  fats.     Their  specific  gravity  is  in  all  cases 
less  than  one,  so  that  they  float  on  water.     They  have  a  fatty 
feel  and  leave  a  permanent  grease  spot  on  paper  or  fabric.     They 
are  almost  insoluble  in  water,  although  water  is  soluble  to  a  not 
inconsiderable  extent  in  fats.     They  are  readily  soluble  in  ether, 
benzol,  carbon  disulphid  and  most  of  them  in  petroleum  ether, 
but  only  sparingly  in  alcohol. 

The  melting  point  of  the  fatty  acids  increases  with  the 
molecular  weight.  The  exact  melting  point  of  a  fat  is  diffi- 
cult to  determine,  but  for  the  three  common  glycerids  and 
the  corresponding  acids  it  may  be  stated  approximately  as 
follows :  — 


THE   COMPONENTS   OF   PLANTS   AND   ANIMALS          19 
MELTING  POINTS 


Olein                                   .     . 

-4°  to  -<' 

3  r 

Oleic  acid 

14°  C 

Palmitin 

63°  to  65' 

3  r 

Palmitic  acid       

62.6°  C. 

Stearin  . 

71.6°  C. 

Stearic  acid 71.5°  C. 

A  distinction  is  commonly  made  between  fats  and  oils,  the 
fats  being  solid  at  ordinary  temperatures  and  the  oils  liquid. 
The  difference  depends  largely  upon  the  proportion  in  which 
the  various  simple  fats  are  present.  Olein  and  other  fats  con- 
taining unsaturated  acids  are  usually  liquid  at  room  temper- 
ature and  their  presence  increases  the  softness  of  the  fat. 

The  fatty  acids  of  higher  molecular  weight  are  volatile  only 
at  comparatively  high  temperatures  and  at  reduced  pressure. 
Those  of  lower  molecular  weight,  notably  those  contained  in  but- 
ter fat,  can  be  readily  distilled  in  a  current  of  steam  and  their 
proportion  serves  to  distinguish  butter  fat  from  other  animal 
fats. 

An  important  physical  property  of  the  fats,  which,  however, 
is  by  no  means  peculiar  to  them,  is  that  of  forming  what  is 
known  as  an  emulsion.  Fat  is  said  to  be  emulsified  when,  in 
the  liquid  state,  it  is  distributed  in  minute  droplets  or  globules 
throughout  some  other  liquid ;  for  example,  if  fat  be  violently 
shaken  with  water  an  emulsion  is  formed.  Such  an  emulsion 
is  not  permanent,  however,  the  fat  droplets  very  soon  coalescing 
and  rising  to  the  surface.  The  presence  of  small  amounts  of 
certain  other  substances  dissolved  in  the  water,  however,  will 
prevent  this  separation  and  give  rise  to  a  permanent  emulsion. 
The  most  common  substance  producing  this  effect  is  soap. 

Certain  gums  and  also  proteins  likewise  serve  to  retain  fat 
in  the  emulsified  state.  The  most  familiar  example  of  such  an 
emulsion  is  milk,  the  fat  being  held  in  suspension  in  this  case 
by  the  action  of  the  proteins  of  the  mUk.  This  effect  of  various 
substances  in  retaining  fat  in  the  emulsified  form  depends  upon 
their  effect  upon  the  surface  tension  of  the  contact  layer  be- 
tween fat  and  water,  but  a  full  discussion  of  this  point  would 
be  out  of  place  in  this  connection. 

33.  Native  fats.  —  As  has  already  been  stated,  the  reserve 
fats  of  the  animal  body  are  triglycerids,  chiefly  of  stearic,  oleic 


20 


NUTRITION  OF  FARM  ANIMALS 


and  palmitic  acids,  although  small  quantities  of  esters  of  lauric, 
myristic  and  arachnic  acids  and  frequently  free  fatty  acids  are 
also  found,  as  well  as  minute  amounts  of  esters  of  the  higher 
alcohols,  coloring  matter,  etc.  Since  stearin  and  palmitin  are 
solid  at  ordinary  temperatures,  while  olein  is  liquid,  the  con- 
sistency of  a  fat  depends  largely  upon  the  proportion  of  olein 
which  it  contains  and  varies  not  only  between  different  species 
of  animals  but  often  in  different  parts  of  the  body  .of  the  same 
animal.  The  fats  of  cold-blooded  animals  contain  more  olein 
than  those  of  warm-blooded  animals  and  therefore  remain  liquid 
at  lower  temperatures. 

The  vegetable  fats  contain  a  greater  variety  of  fatty  acids 
than  the  animal  fats,  notably  unsaturated  acids  like  linoleic 
and  eruic,  as  well  as  oxy-acids  and  esters  of  the  higher  alcohols 
(waxes),  while  the  so-called  crude  fat,  or  ether  extract  (108)  of 
vegetable  materials  contains  a  great  variety  of  ether-soluble 
substances,  including  waxes,  resins,  chlorophyl,  etc.,  some  of 
which  are  but  remotely  related  to  the  true  fats. 

34.  Elementary  composition.  —  The  three  principal  triglyc- 
erids,  stearin,  palmitin  and  olein,  while  differing  in  formula 
and  molecular  weight,  differ  but  little  in  their  elementary  com- 
position, as  the  following  table  shows :  — 


TABLE  i.  —  COMPOSITION  OF  TRIGLYCERIDS 


TRISTEARIN 
% 

TRIPALMITIN 

% 

TRIOLEIN 

% 

Carbon       
Hydrogen 

76.77 

1  2  4.^ 

75.86 

I  2  2A 

77-31 
ii  84. 

Oxygen      

10.78 

11.90 

10.85 

Total      .               ...                   .     . 

TOO  OO 

TOO  OO 

IOO.OO 

Naturally,  therefore,  the  composition  of  the  ordinary  mixed 
animal  fats  varies  but  little,  either  in  different  individuals  or  in 
different  species  of  animals.  The  classic  investigations  of 
Schulze  and  Reinecke1  upon  the  composition  of  animal  fats 
gave  the  following  results. 

1  Landw.  Vers.  Stat.,  9  (1867),  97. 


THE  COMPONENTS  OF  PLANTS  AND   ANIMALS         21 

TABLE  2. —  COMPOSITION  OF  ANIMAL  FATS 


CARBON 

HYDROGEN 

OXYGEN 

No  OF 

SAMPLES 

Aver- 

Maxi- 

Mini- 

Aver- 

Maxi- 

Mini- 

Aver- 

Maxi- 

Mini- 

age 

mum 

mum 
0 

age 

mum 

mum 

age 

mum 

mum 

Beef  fat 

10 

76.50 

76.74 

76.27 

11.91 

12.  II 

11.76 

"•59 

11.86 

ii.  15 

Pork  fat     .     . 
Mutton  fat     . 

6 

12 

76.54 
76.61 

76.78 
76.85 

76.29 
76.27 

11-95 
,12.03 

I2.O7 
12.  l6 

11.86 
11.87 

11.52 
11.36 

".83 
11.56 

".15 

11.00 

Average 

2~8 

76.50 

12.00 

11.50 

Dog.     .     .     . 

76.63 

I2.O5 

11.32 

Cat   .... 

76.56 

11.90 

11.44 

Horse     .     .     . 

76.07 

11.69 

11.24 

Man       .     .     . 

77.62 

11.94 

11.44 

Benedict  and  Osterberg1  obtained  the  following  for  the  com- 
position of  human  fat :  — 

TABLE  3.  —  COMPOSITION  OF  HUMAN  FAT 


CARBON 
% 

HYDROGEN 

% 

Sample  No.  i      

76  20 

II  80 

Sample  No.  2 

76  *6 

Sample  No.  3      

7S  8l 

II  87 

Sample  No.  4      

7c  QC; 

II  85 

Sample  No.  5 

7?    QA 

Sample  No.  6      

?6  O7 

1  1  60 

76  I? 

II  84 

Sample  No.  8      .... 

76  o^ 

ii  81 

Average 

76  08 

ii  78 

The  average  carbon  content  of  animal  fat  is  commonly  con- 
sidered to  be  76.5  per  cent. 

Waxes 

35.  In  popular  usage,  the  distinction  between  fats  and  waxes  is 
based  upon  their  obvious  physical  properties,  substances  having  the 
well-known  greasy  feel  being  called  fats  or  oils  according  to  their 
consistency  at  ordinary  temperatures  while  the  waxes  are  solid,  can 
be  kneaded  and  lack  largely  or  wholly  the  greasy  feel. 

1  Amer.  Jour.  Physiol.,  4  (1901),  69. 


22  NUTRITION  OF  FARM  ANIMALS 

Chemically,  waxes  are  defined  as  fatty  acid  esters  of  alcohols  other 
than  glycerol,  while  the  fats  have  already  been  denned  as  the  fatty 
esters  of  glycerol.  This  distinction  is  far  from  according  with  com- 
mon usage.  Under  it  many  substances  popularly  known  as  waxes 
are  technically  fats,  as  for  example,  Japan  wax  and  in  part  beeswax. 
On  the  other  hand,  numerous  materials  ordinarily  regarded  as  oils  or 
fats  must  be  designated  as  waxes.  One  of  the  most  familiar  bodies 
of  this  class  is  spermaceti,  commonly  regarded  as  a  fat,  which  consists 
chiefly  of  the  palmitic  ester  of  cetyl  alcohol,  CH3(CH2)i4CH2OH,  and 
sperm  oil,  which  contains  no  glycerids,  would  also  be  regarded  as  a 
liquid  wax.  Similarly  wool  fat  is  chemically  a  mixture  of  waxes,  in- 
cluding the  stearic  esters  of  cholesterin  and  isocholesterin.  Beeswax 
is  likewise  in  part  a  true  wax,  containing  the  palmitic  ester  of  myricyl 
alcohol,  CH3(CH2)28CH2OH.  The  secretion  of  the  anal  glands  of 
certain  birds  contains  esters  of  octodeckyl  alcohol,  CisHsyOH. 

Cholesterins 

36.  Substances  of  this  group  are  found  in  the  nonsaponifiable  resi- 
due of  various  fats.     In  the  animal  organism  they  are  found  widely 
distributed  through  the  tissues  in  small  amounts  and  are  appar- 
ently normal  constituents  of  protoplasm.     As  just  noted,  they  are 
especially  abundant  in  wool  fats  in  combination  with  stearic  acid. 
They  are  also  widely  distributed  in  plants.     Their  exact  constitution 
is  still  unknown,  but  they  contain  a  single  alcohol  hydroxyl  and  ap- 
parently belong  to  the  terpene  group.     Their  formula  is  C27H440H, 
or  C2?H460H,  more  probably  the  latter.     From  the  chemical  point 
of  view,  they  are  entirely  unrelated  to  the  other  groups  classified  as 
lipoids,  but  biologically  their  functions  appear  to  be  closely  related 
to  those  of  the  other  ether-soluble  cell  constituents. 

.   Phosphatids  or  Phospholipins 

37.  Lecithins.  —  Quite  closely  related  to  the  fats  are  the 
substances  known  as  lecithins,  which  are  sometimes,  although 
inexactly,  called  phosphorized  fats.     Like  the  fats,  the  leci- 
thins are  esters  of  glycerol.     They  differ  from  the  fats  in  that 
only  two  of  the  hydroxyls  of  the  glycerol  are  replaced  by  fatty 
acid  radicles,   the   third  being   replaced   by  phosphoric   acid 
which  is  also  in  combination  with  the  nitrogenous  base  cholin, 
a  derivative  of  glycol.     The  lecithins,  therefore,  contain,  in 
addition  to  carbon,  hydrogen  and  oxygen,  both  phosphorus  and 
nitrogen. 


THE   COMPONENTS   OF   PLANTS   AND   ANIMALS          23 

The  molecular  structure  of  the  lecithins  is  illustrated  by  the  fol- 
lowing formula  for  distearyl  lecithin :  — 

CH2-0-C18H36O 

I 

CH  -O-Ci8H36O 

I 
CH2-0 

HO-PO 

/ 
CH2-0 

I 

CH2-N  =  (CH3)3 

OH 

The  lecithins  resemble  fats  in  their  general  properties.  They 
are  soluble  in  ether  but,  unlike  the  fats,  readily  form  permanent 
emulsions  or  colloidal  solutions  with  water.  On  hydrolysis, 
they  yield  fatty  acids,  glycero-phosphoric  acid  and  cholin. 
They  are  found  widely  distributed  both  in  animals  and  plants 
and  appear  to  be  essential  constituents  of  protoplasm. 

38.  Other  phosphatids.  —  A  variety  of  other  lipoids  of  the  type  of 
the  lecithins,  but  differing  in  both  the  fatty  acid  and  the  nitrogenous 
base  which  they  contain  and  likewise  in  the  ratio  of  phosphorus  to 
nitrogen,  have  been  described,  but  the  chemistry  of  this  group  is  still 
in  a  very  unsatisfactory  state.  The  various  phosphatid  preparations 
obtained  from  vegetable  materials,  especially  seeds,  by  E.  Schulze 
and  his  associates  and  designated  as  lecithins  are  held  by  other 
authors  to  be  such  only  in  a  generic  sense  and  in  some  cases  are  re- 
garded as  more  analogous  to  the  cerebrosids  or  galactolipins  of  the 
succeeding  paragraph. 

Cerebrosids  or  Galactolipins 

39.  This  group  of  substances,  found  especially  in  the  brain  and  in 
nerve  tissue  in  general,  belongs  chemically  to  the  lipoids,  since  its 
members  yield  fatty  acids  on  hydrolysis.  The  other  products  of 
hydrolysis  are  galactose  and  nitrogenous  substances  but  no  phosphoric 
acid,  but  the  constitution  of  these  compounds  is  still  unknown. 


24  NUTRITION  OF  FARM  ANIMALS 

§  4.   THE  PROTEINS 

40.  Importance.  —  By  far  the   larger  share  of  the  organic 
matter  of  the  animal  body,  aside  from  fat,  consists  of  sub- 
stances belonging  to  the  well-defined  group  of  the  proteins, 
these  compounds,  according  to  the  results  of  analyses  recorded 
on  subsequent  pages  (98),  making  up  from  17.5  to  21  per  cent 
of  the  fat-free  body.     These  substances  are  characteristic  of 
the  animal  body,  as  the  carbohydrates  are  of  plants.     Biologi- 
cally, they  are  of  prime  importance  to  both  plants  and  animals, 
since  they  form  the  basis  of    the  cytoplasm  and  nucleus  of 
every  living  cell. 

41.  Nomenclature.  —  The   chemical   structure   of   the  pro- 
tein molecule  has  until  quite  recently  been  almost  entirely  un- 
known and  even  yet  has  been  but  very  partially  unraveled. 
Accordingly,  the  basis  for  a  scientific  classification  of  these 
substances  has  been  lacking.     As  a  matter  of  necessity,  there- 
fore, the  nomenclature  hitherto  followed  has  been  based  chiefly 
on  their  physical  properties,  more  particularly  their  solubilities 
and  coagulation  temperatures.     Naturally,  such  a  classification 
has  been  far  from  satisfactory  and  this  has  been  the  more  true 
on  account  of  the  difficulty  of  accurately  separating  the  differ- 
ent proteins  either  by  precipitation  or  crystallization. 

Accordingly,  there  has  existed  a  great  and  confusing  diversity 
in  the  nomenclature  of  the  proteins,  and  uniformity  is  still  far 
from  having  been  reached.  For  the  present,  it  seems  desirable 
to  follow  the  classification  and  nomenclature  which  has  been 
adopted  provisionally  by  the  American  Physiological  Society1 
and  the  American  Society  of  Biological  Chemists.2  This 
nomenclature  rejects  entirely  the  term  proteid  as  ambiguous 
on  account  of  the  wide  diversity  in  its  use,  and  employs  protein 
as  a  general  term  to  signify  the  group  of  substances  which, 
according  to  the  nomenclature  adopted  by  the  Association  of 
American  Agricultural  Colleges  and  Experiment  Stations  in 
1 8g8,3  was  called  proteids.  In  other  words,  protein  under  the 
new  plan  excludes  altogether  the  non-protein  nitrogenous 
substances  of  plants  and  animals. 

1  Proceedings,  Amer.  Physiol.  Soc.,  Amer.  Jour.  Physiol.,  21  (1908),  xxvii. 

2  Proceedings,  Amer.  Soc.  Biol.  Chemists,  1,  142. 

3  U.  S.  Dept.  Agr.,  Office  of  Expt.  Stas.,  Bui.  65,  pp.  117-123. 


THE  COMPONENTS  OF  PLANTS  AND   ANIMALS         25 

The  proteins  in  this  sense  are  subdivided  into :  — 

1.  Simple  proteins 

2.  Conjugated  proteins 

3.  Derived  proteins 

Simple  proteins  are  denned  as  those  yielding  only  a 
amino  acids  or  their  derivatives  upon  hydrolysis.  Conju- 
gated proteins  are  those  which  contain  the  protein  mole- 
cule united  to  some  other  molecule  or  molecules  otherwise  than 
as  a  salt.  Derived  proteins  are  the  products  of  the  hydrolytic 
cleavage  of  the  protein  molecule  and  include  a  wide  range  of 
substances,  from  slightly  altered  protein  to  the  peptids. 

42.  Physical  properties.  —  In  the  dry  state,  the  proteins  are 
in  general  white  or  slightly  tinted  substances.  They  are  usually 
amorphous,  but  a  number  of  them  have  also  been  obtained  in 
the  crystalline  form  and  some  are  found  crystallized  in  nature. 
Some  of  the  proteins  are  soluble  in  water,  others  only  in  salt 
solutions  or  in  acids  or  alkalies.  They  are  insoluble  in  most 
other  ordinary  solvents. 

The  proteins  belong  to  the  class  of  colloids,  i.e.,  they  do  not 
diffuse  through  membranes  and  are  claimed  to  have  no  osmotic 
pressure  when  free  from  electrolytes.  Colloids  in  general  exist 
in  two  forms,  a  liquid  form,  technically  known  as  a  sol,  and  a 
solid  form  called  a  gel,  the  difference  being  well  illustrated  by 
the  familiar  substance  gelatin.  When  a  colloid  is  distributed 
through  water  so  as  to  form  an  apparent  solution  the  latter  is 
known  as  a  hydrosol.  Whether  the  proteins  are  to  be  regarded 
as  soluble  in  water,  or  whether  their  apparent  solution  is  in 
reality  a  suspension,  has  been  much  discussed.  It  has  been 
shown,  however,  that  these  solutions  are  conductors  of  electricity 
and  it  has  been  concluded  that  they  are  true  solutions.  It  may 
be  said,  however,  that  no  sharp  boundary  exists  between  a 
true  solution  and  a  suspension  but  that  an  indefinite  number  of 
intermediate  stages  is  possible.  As  a  matter  of  convenience, 
however,  we  may  speak  of  solutions  of  the  proteins. 

Different  proteins  may  be  precipitated  from  their  solutions 
by  various  reagents,  particularly  acids,  alkalies  and  metallic 
salts.  Ammonium  sulphate,  especially,  has  been  largely  used 
for  the  purpose  of  separating  different  proteins  by  means  of 
fractional  precipitation. 


26  NUTRITION  OF  FARM  ANIMALS 

43.  Coagulation.  —  An  important  property  of  the  proteins 
is  that  of  coagulation.     For  instance,  if  a  solution  of  ordinary 
egg  albumin  be  heated  to  55°  C.  the  albumin  begins  to  separate 
in  an  insoluble  form  and  at  about  6'o°  C.  the  precipitation  is 
complete.     This  change  differs  from  the  change  in  the  case  of 
gelatin  solutions  from  liquid  to  solid  in  being  irreversible,  i.e., 
coagulated  protein  cannot  be  changed  back  to  the  soluble  form. 
It  should  be  noted  that  this  change  is  entirely  distinct  from  the 
precipitation  of  proteins  by  means  of  ammonium  sulphate  for 
example.     The  exact  nature  of  the  change  is  unknown,  but  it 
would  seem  to  be  in  part  chemical  in  character. 

All  forms  of  protein  appear  to  be  subject  to  coagulation  in 
the  chemical  sense  of  the  word.  Thus  the  precipitated  proteins 
obtained  from  solutions  are  at  first  in  the  colloidal  form  but  on 
standing  pass  more  or  less  rapidly  into  the  coagulated  or  "  de- 
natured "  form.  The  same  is  true  of  the  solid  proteins  like 
fibrin,  etc.  The  coagulated  proteins  are  insoluble  in  water 
and  salt  solutions,  but  may  be  dissolved  in  acids  or  alkalies. 

The  simple  proteins 

44.  Composition.  —  The  simple  proteins  differ  from  the  com- 
pounds considered  in  the  previous  sections  in  containing,  in 
addition  to  carbon,  hydrogen  and  oxygen,  the  elements  nitro- 
gen and  sulphur.     Notwithstanding  the  considerable  variation 
in  the  properties  of  the  different  simple  proteins  and  the  notable 
differences  which  have  been  shown  to  exist  in  their  chemical 
structure,    their    elementary    composition    differs    but    little. 
Cohnheim  1  quotes  the  following  figures  from  Michel  for  the 
composition  of  serum  albumin,  which  is  in  many  respects  a 
typical  animal  protein. 

Carbon 53-o8 

Hydrogen 7.10 

Nitrogen 15.93 

Sulphur 1.90 

Oxygen 21.99 

100.00 

The  variations  in  the  percentages  of  the  principal  elements 
as  stated  by  Cohnheim 1  and  by  Plimmer 2  are :  — 

1  Chemie  der  Eiweisskorper,  2d  Ed.,  p.  151. 

*  The  Chemical  Constitution  of  the  Proteins,  Part  I,  p.  2. 


THE   COMPONENTS  OF   PLANTS  AND   ANIMALS         27 


COHNHEIM 

PLIMMER 

Carbon 

r2-^q% 

ei-ec% 

Nitrogen  
Hydrogen 

15-19% 

15-17% 
n®7 

Sulphur     ....          ... 

o  4—2.0%  1 

O.A—2.=;% 

As  a  rule,  the  vegetable  proteins  contain  a  higher  percentage 
of  nitrogen  than  do  the  animal  proteins. 

45.  Structure  of  the  proteins.  —  The  molecular  structure  of 
the  proteins  is  very  complex  and  their  molecular  weights  are 
very  large,  but  as  yet  no  very  satisfactory  determinations  of  the 
latter  magnitude  have  been  made.  Determinations  of  the 
molecular  structure  of  haemoglobin  (a  conjugated  protein)  by 
two  methods  have  given  concordant  results  indicating  a  mini- 
mum molecular  weight  of  16,666,  from  which  has  been  computed 
the  formula  C758H12o3Ni95FeS2.  Confirmation  of  this  result  has 
been  reported  as  the  result  of  determinations  of  its  osmotic 
pressure.2  For  the  globin  of  haemoglobin,  a  minimum  molecu- 
lar weight  of  between  5000  and  8000  has  been  obtained.  For 
serum  albumin,  the  figure  10,166  is  reported,  for  egg  albumin, 
5378,  and  for  edestin  14,500.  These  figures  are  of  value,  how- 
ever, chiefly  as  showing  the  complex  nature  of  the  protein  mole- 
cule. 

Up  to  within  a  comparatively  few  years,  general  statements 
like  those  just  made  marked  the  limits  of  our  knowledge  of  the 
chemical  nature  of  the  proteins.  The  masterly  researches  of 
Emil  Fischer,  however,  and  especially  his  creation  of  new 
experimental  methods,  have  resulted  in  a  very  great  advance 
in  knowledge,  and  to-day,  thanks  to  his  labors  and  those  of  a 
large  number  of  investigators  in  applying  and  improving  his 
methods,  we  possess  a  fairly  definite  general  conception  of  the 
structure  of  the  protein  molecule.  As  in  the  investigation  of 
chemical  compounds  in  general,  two  lines  of  attack  have  been 
followed,  viz.,  a  study  of  the  products  resulting  from  the 
splitting  up  of  the  molecule  and  attempts  to  synthesize  the 
compound  from  simpler  substances  of  known  composition  and 
structure. 

1  Four  to  five  per  cent  in  keratins.  2  Zentbl.  Physiol.,  21,  730. 


28  NUTRITION  OF  FARM   ANIMALS 

46.  Hydrolysis  of  proteins.  —  The  simple  proteins  readily 
undergo  hydrolysis  when  acted  upon  by  strong  acids  or  alkalies, 
or  by  various  enzyms  such  as  the  pepsin  of  the  gastric  juice, 
the  trypsin  of  the  pancreatic  juice,  etc.     These  various  agents 
effect  a  succession  of  cleavages  and  hydrations  resulting  in  a 
series  of  products  of  decreasing  molecular  complexity  and  in- 
creasing solubility,  ranging  from  very  slightly  modified  proteins 
through  the  so-called  proteoses  and  peptones  to  still  simpler 
substances. 

47.  Cleavage  products  of  proteins.  —  When  the  hydrolysis, 
especially  acid  hydrolysis,  of  the  simple  proteins  is  pushed  as 
far  as  possible,  there  result  a  number  of  comparatively  simple 
crystalline  substances  which  are  qualitatively  the  same  for  all 
proteins  with  a  few  exceptions,  although  the  proportions  of  the 
various  products  obtained  from  different  proteins  vary  ma- 
terially.    It  is  believed,  therefore,  that  the  protein  molecule  is 
built  up  of  these  final  products  of  hydrolysis,  the  so-called 
"  building  stones." 

These  primary  cleavage  products  of  the  simple  proteins  are 
all  a  amino  acids.  One  of  the  first  of  them  to  be  isolated  was 
glycin  or  aminoacetic  acid,  represented  by  .the  following  for- 
mula :  — 

CH3  CH2  •  NH2 

I  I 

COOH  COOH 

Acetic  acid  Glycin 

The  other  cleavage  products  of  the  simple  proteins  may  be 
regarded  as  derived  from  glycin  by  the  replacement  of  one 
atom  of  hydrogen  in  the  CH2  group  by  various  atomic  group- 
ings. In  all  of  them  the  NH2  group  occupies  the  same  position 
in  the  molecule  relative  to  the  group  COOH  as  in  glycin,  the 
so-called  a  position.  The  atomic  grouping 


CH  -  NH2 

I 

CO -OH 

is  therefore  common  to  all  of  these  bodies  and  determines  their 
general  chemical  behavior  as  well  as  that  of  the  proteins  from 
which  they  are  derived. 


THE  COMPONENTS   OF  PLANTS  AND  ANIMALS          29 

The  amino  acids  derived  from  the  proteins  may  be  divided 
into  two  classes ;  the  monamino  acids,  of  which  glycin  is  typi- 
cal, containing  one  NH2  group,  and  the  diamino  acids,  contain- 
ing two  NH2  groups.  To  these  there  are  to  be  added  certain 
heterocyclic  compounds.  Plimmer 1  gives  the  following  list  of 
the  amino  acids  which  have  been  identified  with  certainty  among 
the  cleavage  products  of  the  proteins.  The  presence  of  others 
has  been  claimed  by  several  investigators. 

A.  Monoaminomonocarboxylic  acids 

1.  Glycin,  C2H5NO2,  or  aminoacetic  acid. 

CH2  •  (NH2)  •  COOH 

2.  Alanin,  C3H7NO2,  or  a-aminopropionic  acid. 

CH3  •  CH(NH2)  •  COOH 

3.  Valin,    C5HnNO2,  or  a-aminoisovalerianic  acid. 

CH3\ 

^CH  •  CH(NH2)  •  COOH 
CH3/ 

4.  Leucin,  C6Hi3NO2  or  a-aminoisocaproic  acid. 

CH3\ 

CH  •  CH2  •  CH(NH2)  •  COOH 
CH3/ 

5.  Isoleucin,  C6Hi3NO2,  or  a-amino-/3-methyl-/3-ethyl-propionic  acid. 

CH3\ 

CH  •  CH(NH2)  -  COOH 
C2H5/ 

6.  Phenylalanin,  C9HnNO2,  or  /3-phenyl-a-aminopropionic  acid. 

C6H5  •  CH2  •  CH(NH2)  •  COOH 

7.  Ty rosin,    C9HnNO3,   or  0-parahydroxyphenyl-a-aminopropionic 
acid.  HO  •  C6H4  •  CH2  •  CH(NH2)  •  COOH 

8.  Serin,     C3H7NO3,  or  0-hydroxy-a-aminopropiomc  acid. 

CH2(OH)  •  CH(NH2)  •  COOH 

9.  Cystin,  C6Hi2N2O4S2,  or  dicysteine,  or  di-  (/3-thio-a-aminopro- 
pionicacid)  HOOC  •  CH(NH2)  •  CH2  •  S  — S  •  CH2  •  CH(NH2)  •  COOH 

B.   Monoaminodicarboxylic  acids 

10.  Aspartic  acid,  C^rNO^  or  a  aminosuccinic  acid. 

HOOC  •  CH2  •  CH(NH2)  •  COOH 

11.  Glutamic  acid,  C5H9NO4,  or  a-aminoglutaric  acid. 

HOOC  •  CH2  -  CH2  •  CH(NH2)  •  COOH 

1The  Chemical  Constitution  of  the  Proteins,  Part  I,  ad  Ed.,  1912. 


30  NUTRITION   OF   FARM  ANIMALS 

C.   Diaminomonocarboxylic  acids 

12.  Arginin,  C6Hi4N4O2,  or  a-amino-y-guanidin  valerianic  acid. 

HN=C/NH2 

NH  •  CH2  •  CH2  •  CH2  •  CH(NH2)  •  COOH 

13.  Lysin,  CoHi4N2O2  or  a,  e-diaminocaproic  acid. 

H2N  •  CH2  •  CH2  •  CH2  •  CH2  •  CH(NH2)  •  COOH 

D.   Heterocyclic  compounds 

14.  Histidin,  CeHgNsO^  or  /S-imidazol-a-aminopropionic  acid. 

CH 

^      \ 

N  NH 

I  I 

CH  =      C  —  CH2  •  CH(NH2)  •  COOH. 

15.  Prolin,  C5H9NO2,  or  -pyrrolidin  carboxylic  acid 

CH2  —  CH2 

I  I 

CH2      CH  •  COOH 

\        / 
NH 

1 6.  Oxyprolin,  or  oxypyrrolidine  carboxylic  acid. 

C5H9N03 

17.  Tryptophan,  CnHt2N2O2,  or  jS-indol-a-aminopropionic  acid. 

C  —  CH2  •  CH(NH2)  •  COOH 

/\ 
CCH4        CH 

\   / 
NH 

48.  Synthesis  of  proteins.  —  Peptids.  —  Fischer  and  others 
have  shown  that  the  amino  acids  which  result  from  the  cleavage 
of  the  simple  proteins  may  combine  with  each  other,  the  NH2 
of  one  uniting  with  the  COOH  group  of  the  other  with  the 
elimination  of  one  molecule  of  water.  As  many  as  18  molecules 
of  amino  acids  have  been  combined  in  this  way,  although  the 
exact  structure  of  the  resulting  compounds  is  still  more  or  less 
uncertain. 

The  compounds  of  the  amino  acids  which  have  been  prepared 
artificially  have  received  the  general  name  of  peptids,  the  pre- 
fixes di-,  tri-,  etc.,  being  used  to  indicate  the  number  of  amino 
acid  molecules  entering  into  the  compound.  The  term  poly- 


THE   COMPONENTS   OF   PLANTS   AND   ANIMALS         31 

peptids  is  also  commonly  used  as  a  general  term  for  the  more 
complex  substances  of  this  group.  The  latter  show  many  of 
the  reactions  of  the  proteins  or  of  their  less  modified  deriva- 
tives. For  example,  many  of  them  give  the  biuret  reaction 
characteristic  of  the  proteins,  are  precipitated  by  phospho- 
tungstic  acid  and  undergo  cleavage  by  appropriate  proteolytic 
ferments.  Moreover,  some  of  the  artificial  polypeptids  of  known 
composition  have  also  been  isolated  from  the  mixture  of  products 
resulting  from  the  action  of  ferments  upon  the  proteins. 

49.  Conclusions.  —  Since,  therefore,  the  same  comparatively 
simple  crystalline  products  are  obtained  as  the  final  result  of 
the  complete  hydrolysis  of  all  the  simple  proteins,  viz.,  the 
various  amino  acids  enumerated  in  a  previous  paragraph  (47), 
and  since,  on  the  other  hand,  these  cleavage  products  may  be 
synthesized  to  form  substances  closely  resembling  the  proteins, 
it  is  believed  that  the  protein  molecule  is  built  up  of  these 
amino  acids,  united  in  substantially  the  same  way  as  in  the 
artificially  prepared  polypeptids.     In  other  words,   it  is  be- 
lieved that  the  latter  are  the  first  steps  toward  the  synthesis 
of  proteins,  or  indeed  that  they  may,  from  a  systematic  point 
of  view,  be  regarded  as  the  simplest  of  the  proteins. 

It  should  be  noted,  however,  that  while  the  foregoing  method  of 
combination  of  the  amino  acids  appears  to  be  characteristic  of  the 
protein  molecule,  it  is  not  the  only  form  of  combination  in  which 
nitrogen  enters  into  it.  For  example,  arginin,  apparently  a  constit- 
uent of  all  proteins,  contains  an  atom  of  imid  nitrogen,  HN.  The 
proteins  also  contain  amid  nitrogen  (i.e.,  NH2  substituted  for  the  OH 
of  the  carboxyl  group)  which  yields  ammonia  on  hydrolysis.  Further- 
more, the  proteins  are  capable  of  acting  as  polyacid  bases  and  there- 
fore the  molecule  must  contain  numerous  NH2  end-groups  such  as 
that  of  the  amids  just  mentioned  or  those  of  the  diamino-acids  like 
lysin  and  arginin. 

50.  Proportions  of  cleavage  products  in  different  proteins.  — 

While  all  the  simple  proteins  yield,  with  a  few  exceptions, 
qualitatively  the  same  cleavage  products,  the  relative  pro- 
portions of  these  "  building  stones  "  vary  widely  in  proteins 
from  different  sources.  This  is  strikingly  illustrated  by  the 
following  tabulation  of  the  percentages  of  the  various  amino 
acids  yielded  by  a  number  of  proteins  according  to  the  researches 
of  Osborne  and  his  associates. 


32  NUTRITION  OF   FARM   ANIMALS 

TABLE  4.  —  CLEAVAGE  PRODUCTS  OF  PROTEINS  * 


1 

1 

a 

1 

1 

g 
p 

§    M 

^ 

o 

^ 

M 

PQ 

^     *S 

U 

II 

ll 

I 

1-1 

o 

^ 

s  - 

w  S 

w    P 

s 

M   EJ 
O   en 

• 

sS 

3  5 

o£ 

35 

%l 

1 

* 

<    0 
00 

fi 

ss 

Glycin  

0.00 

0.89 

o.oo 

0.38 

0.0 

o.o 

0.00 

2.06 

0.68 

Alanin 

2.OO 

4.65 

1  3  30 

2.08 

2.22 

2   ?O 

1.50 

3-72 

2.28 

Valin     

3-34 

0.24 

1.88 

2.50 

o'oo 

7.20 

0.81 

Leucin 

6.62 

C.QC 

19.  cc 

8.00 

IO.7I 

IQ  40 

11.65 

I  I.IQ 

Phenylalanin  .... 

2-35 

0  "VO 

1.97 

V   0  O 

6.55 

3-75 

5-07 

2.40 

3.20 

3-53 

Tyrosin     

1.50 

4.25 

3-55 

1-55 

1.77 

2.  2O 

4.50 

2.20 

2.16 

Serin 

0.13 

0.74 

i.  02 

0^3 

•J) 

-j> 

o  ^o 

•^ 

p 

Cystin 

w-  *O 

0.45 

O.O2 

J_ 

^> 

p 

J> 



Prolin   

13.22 

4-23 

9.04 

3.22 

3-56 

4.00 

6.70 

5-82 

4-74 

Aspartic  acid  .... 

0.58 

0.91 

1.71 

5-30 

2.20 

I.OO 

i-39 

4.51 

3-21 

Glutamic  acid     .     .     . 

43-66 

23.42 

26.17 

13.80 

9.10 

10.10 

15-55 

15-49 

16.48 

Tryptophan  .... 

I.OO 

+ 

o.oo 

+ 

+ 

+ 

1.50 

+ 

+ 

Arginin 

«  16 

4.72 

i.cc 

IO.I2 

A  OI 

„  o_ 

„  gy 

7  47 

6.50 

Lysin    

J> 

*T-  / 

I.Q2 

00 

o.oo 

4.98 

3.76 

8.10 

7.61 

/  •**  / 
7*  S9 

7  24, 

Histidin     

1.49 

-y 
1.76 

0.82 

*T*y  w 

2.42 

Of 

1.71 

i-53 

/  * 

2.50 

1.76 

/  ••£ir 

2-47 

Ammonia 

5-22 

4  OI 

-    £.. 

I  no 

i.  24 

I   12 

1.61 

I    O7 

I  67 

Total    

*!•• 

•$•    4 

vv 

"« 

J..V-*  / 

i  ,VJ  ^ 

84.72 

59-68 

88.87 

58.12 

48.85 

56.46 

66.92 

67.29 

62.15 

The  results  shown  in  the  foregoing  table  are  typical.  In  a 
few  proteins,  certain  amino  acids  have  not  been  found  at  all. 
For  example,  no  glycin  has  been  found  among  the  products  of 
the  hydrolysis  of  gliadin,  zein,  albumin  or  casein  and  no  lysin 
among  those  of  gliadin  or  zein.  Furthermore,  the  proportion  of 
the  various  cleavage  products  is  quite  variable  in  the  different 
proteins,  one  of  the  most  striking  instances  being  that  of  glu- 
tamic  acid  which  ranges  from  nearly  44  per  cent  in  the  gliadin 
of  wheat  to  a  little  over  9  per  cent  in  egg  albumin,  and  is  no- 
tably more  abundant  in  vegetable  than  in  animal  proteins. 

51.  Classification.  —  For  the  present  purpose,  it  seems  super- 
fluous to  enter  into  a  full  description  of  the  various  simple  pro- 

1  The  sign  +  signifies  that  the  substance  was  present  but  was  not  quantitatively 
determined.  A  blank  simply  indicates  that  the  ingredient  in  question  was  not 
determined  but  does  not  show  that  it  was  not  present. 


THE  COMPONENTS  OF  PLANTS  AND  ANIMALS         33 

teins.     The  principal  groups  into  which  they  are  subdivided  are 
designated  as  follows :  — 

a.  Albumins.  —  These  are  simple  proteins  soluble  in  pure 
water  and  coagulable  by  heat.     Besides  the  familiar  egg  al- 
bumin, they  include  the  albumins  of  blood  serum  and  of  milk 
serum.     Albumins  have  also  been  found  in  small  amounts  in 
a  great  variety  of  seeds,  including  those  of  wheat,  rye,  barley, 
pea,  vetch,  soybean  and  cowpea. 

b.  Globulins.  —  The  globulins  are  simple  proteins  insoluble 
in  pure  water  but  soluble  in  neutral  solutions  of  salts  of  strong 
bases  with  strong  acids.     Globulins  are  found  in  the  lymph 
and  the  blood  serum  and  in  the  muscles  and  other  organs,  but 
they  appear  to  be  especially  characteristic  of  the  vegetable 
kingdom,  occurring  in  considerable  amounts  in  a  large  number 
of  seeds.     Osborne 1  gives  a  list  of  1 5  globulins  occurring  in  24 
different  species  of  seeds  and  enumerates  12  additional  species 
which  contain  globulins  to  which  no  distinctive  names  have 
yet  been  given. 

c.  Glutelins.  —  These  are  defined  as  simple  proteins  insoluble 
in  all  neutral  solvents  but  readily  soluble  in  very  dilute  acids 
and  alkalies.     The  only  well-defined  members  of  this  group  at 
present  known  are  the  glutenin  of  wheat  and  the  oryzenin  of 
rice,  although  there  seems  reason  to  believe  that  similar  pro- 
teins exist  in  the  seeds  of  other  cereals. 

d.  Prolamins,  or  alcohol-soluble  proteins.  —  The  typical  mem- 
ber of  this  group  is  the  gliadin  of  wheat  and  the  name  has 
been  applied  by  some  authors  to  the  entire  group,  but  the 
term  prolamins,  proposed  by  Osborne,  seems  preferable.     The 
prolamins  are  soluble  in  relatively  strong  alcohol  (70-80  percent) 
but  insoluble  in  water,  absolute  alcohol  and  other  neutral  sol- 
vents.    They  are  characteristic  of  the  seeds  of  the  cereals,  the 
principal  prolamins  being  the  gliadin  of  wheat  and  rye,  the 
hordein  of  barley,  the  zein  of  maize  and  the  bynin  of  malt. 

e.  Albuminoids.  —  This  name,  formerly  used  to  a  consider- 
able extent  as  practically  synonymous  with  proteins,  is  now 
applied  to  two  groups  of  nitrogenous  substances  which  have 
been  otherwise  designated  as  the  collagens,  or  gelatinoids,  and 
the  keratins.     Albuminoids  are  defined  as  simple  proteins  which 
possess  essentially  the  same  chemical  structure  as  the  other 

1  The  Vegetable  Proteins,  p.  78. 


34  NUTRITION  OF  FARM  ANIMALS 

proteins  but  are  characterized  by  great  insolubility  in  all 
neutral  solvents.  They  form  the  principal  organic  constituents 
of  the  skeletal  structures  of  animals  and  of  their  external  cover- 
ing and  its  appendages  and  hence  have  also  been  called  sclero- 
proteins.  This  definition  does  not  provide  for  gelatin,  which 
is,  however,  an  artificial  derivative  of  collagen.  Besides  gela- 
tin the  more  important  members  of  this  group  are  chondrin, 
or  collagen,  which  constitutes  the  organic  basis  of  cartilage  and 
bone;  elastin,  the  characteristic  component  of  the  ligaments; 
and  the  keratins  of  the  epidermal  tissues  such  as  hair,  wool, 
feathers,  horns,  hoofs,  etc. 

The  conjugated  proteins 

52.  Nucleoproteins.  —  In  the  scheme  of  classification  here 
followed  (41),  the  nucleoproteins  are  defined  as  follows :  "  These 
proteins   are   especially   characteristic   of   the  nucleus   of   the 
vegetable  and  animal  cell  (74).     They  consist  of  protein  mole- 
cules united  with  one  or  more  of  the  compounds  known  as 
nucleic  acids.     These  are  complex  organic  compounds  contain- 
ing a  phosphoric  acid  radicle  and  also  a  xanthin  group." 

The  simple  proteins  of  the  nucleoproteins  apparently  may  be 
of  quite  diverse  nature  and  belong  to  various  groups  of  the 
simple  proteins.  The  special  interest  of  the  nucleoproteins 
attaches  to  the  nucleic  acids  entering  into  their  composition. 

53.  Nucleic  acids.  —  These  compounds  contain  in  addition 
to  carbon,  hydrogen,  nitrogen  and  oxygen  the  element  phos- 
phorus.    Their  constitution  has  not  yet  been  fully  worked  out, 
but  their  cleavage  yields  four  classes  of  products,  viz., 

1.  Xanthin,  or  purin,  bases 

2.  Pyrimidin  bases 

3.  A  pentose  carbohydrate 

4.  Phosphoric  acid 

According  to  the  recent  investigations  of  Levene  and  others, 
the  nucleic  acid  molecule  may  be  regarded  as  built  up  from 
nucleosids,  or  glucosid-like  combinations  of  a  pentose  carbohy- 
drate with  a  purin  or  pyrimidin  base.  By  the  union  of  such  a 
nucleosid  with  phosphoric  acid  there  is  formed  a  nucleotid. 
Finally,  the  most  common  nucleic  acids  are  tetranucleotids. 


THE   COMPONENTS  OF  PLANTS  AND   ANIMALS         35 

which  seem  always  to  contain  both  purin  and  pyrimidin  nucleo- 
sids. 

54.  Glycoproteins.  —  The  glycoproteins  are  denned  as  "  Com- 
pounds of  the  protein  molecule  with  a  substance  or  substances 
containing  a  carbohydrate  group  other  than  a  nucleic  acid. 
The  principal  compounds  of  this  group  are  the  mucins  and  the 
mucoids." 

55.  Phosphoproteins.  —  These  are  denned  as  compounds  of 
the  protein  molecule  with  some,  as  yet  undefined,  phosphorus- 
containing  substance  other  than  a  nucleic  acid  or  lecithin. 
The  casein,  or  rather  caseinogen,  of  milk  is  one  of  the  most 
familiar  and  important  of  this  group. 

56.  Haemoglobins.  —  The  haemoglobins  are  compounds    of 
the  protein  molecule  with  hsematin  or  some  similar  substance, 
and  constitute  the  red  coloring  matter  of  the  blood. 

57.  Lecithoproteins.  —  Compounds  of  the  protein  molecule 
with  lecithins. 

The  derived  proteins 

58.  Primary  protein  derivatives.  —  Derivatives  of  protein  ap- 
parently formed  through  hydrolytic  changes  which  involve  only  slight 
alterations  of  the  molecule. 

Proteans.  —  Insoluble  products  which  apparently  result  from  the 
incipient  action  of  water,  very  dilute  acids  or  enzyms. 

Metaproteins.  —  Products  of  the  further  action  of  acids  and  alkalies 
whereby  the  molecule  is  so  far  altered  as  to  form  products  soluble  in 
very  weak  acids  and  alkalies  but  insoluble  in  neutral  fluids.  This 
group  will  thus  include  the  familiar  "acid  proteins"  and  " alkali  pro- 
teins," not  the  salts  of  proteins  with  acids. 

Coagulated  proteins.  —  Insoluble  products  which  result  from  (i)  the 
action  of  heat  on  their  solutions,  or  (2)  the  action  of  alcohols  on  the 
protein. 

59.  Secondary  protein  derivatives.  —  Products  of  the  further 
hydrolytic  cleavage  of  the  protein  molecule. 

Proteases.  —  Soluble  in  water,  uncoagulated  by  heat,  and  pre- 
cipitated by  saturating  their  solutions  with  ammonium  or  zinc 
sulphate. 

Peptones.  —  Soluble  in  water,  uncoagulated  by  heat  but  not  pre- 
cipitated by  saturating  their  solutions  with  ammonium  sulphate. 

Peptids.  —  Definitely  characterized  combinations  of  two  or  more 
amino  acids,  the  carboxyl  group  of  one  being  united  with  the  ammo 
group  of  the  other  with  the  elimination  of  a  molecule  of  water  (48). 


36  NUTRITION  OF  FARM  ANIMALS 


§  5.   THE  NON-PROTEINS 

60.  Occurrence. —  In  addition  to  the  proteins,  both  plants 
and  animals  contain  a  great  variety  and  sometimes  relatively 
considerable  amounts  of  nitrogenous  compounds  of  the  most 
diverse  nature.     While  the  occurrence  of  such  compounds,  es- 
pecially in  feeding  stuffs,  was  known  from  an  early  day,  it  was 
long  assumed  that  the  amounts  present  were  relatively  insignifi- 
cant and  that  no  material  error  was  involved  in  regarding  all 
the  nitrogen  of  a  feeding  stuff  as  existing  in  the  form  of  protein. 
Accordingly,  the  total  nitrogen  multiplied  by  the  conventional 
factor  6.25  and  designated  as  "  crude  protein  "  was  taken  as 
representing  the  true  protein  content  of  the  material.     The 
researches  of  Scheibler,  E.  Schulze  and  Kellner  in  the  seventies, 
however,  showed  that  this  was  far  from  being  the  case.     It 
was   found   that   nitrogenous   substances   other   than   protein 
were  very  widely  distributed  and  that  sometimes  as  much  as 
one-third  or  even  one-half  of  the  total  nitrogen  of  feeding 
stuffs  existed  in  these  non-protein  compounds.     These  results 
have  been  fully  confirmed  by  subsequent  investigations  and  it 
has  therefore  become  necessary  to  distinguish  between  these 
substances  and  the  true  proteins. 

61.  Definition.     General  properties.  —  While  these  nitrog- 
enous compounds  other  than  protein  are  of  the  most  varied 
nature,  they  all  differ  from  the  proteins  in  having  a  much  less 
complex  molecular  structure.     Many  are  comparatively  simple, 
crystalline  substances,  most  of  them  readily  soluble  in  water 
and  diffusible,  and  they  appear  distinctly  inferior  in  nutritive 
value  to  the  proteins.     It  is  a  matter  of  practical  convenience, 
therefore,  to  have  a  group  name  by  which  to  distinguish  them 
and  for  this  purpose  the  term  non-proteins  has  been  proposed. 
It  is,  of  course,  a  contraction  for  non-protein  nitrogenous  sub- 
stances and  means  simply  substances  which  contain  nitrogen 
but  are  not  proteins.     It  therefore  includes  a  great  variety  of 
compounds  and  may  be  considered  as  in  a  sense  a  cover  for 
our  ignorance   of   their   exact   nature.     The  more  important 
groups  of  non-proteins  are :  — 

The  nitrogenous  muscle  extractives 
The  nitrogenous  lipoids 


THE   COMPONENTS  OF  PLANTS  AND   ANIMALS         37 

The  nitrogenous  glucosids 
Alkaloids  and  organic  bases 
Amino  acids  and  amids 
Nitrates  and  ammonium  salts 

62.  The  muscle  extractives.  —  The  more  important  nitrog- 
enous muscle  extractives  are  creatin,  creatinin  and  the  purin 
bases  xanthin  and  hypoxanthin. 

63.  Nitrogenous    lipoids.  —  As    noted    (37-39),    the    lipoid 
group  includes  a  number  of  compounds,  classed  as  phosphatids 
and  cerebrosids,  which  contain  a  nitrogenous  group  in  combi- 
nation with  fatty  acid  radicles.     The  most  familiar  members  of 
this  group  are  the  lecithins.     The  actual  amounts  of  these  sub- 
stances contained  either  in  the  animal  or  plant  are  small  and 
their  nitrogen  does  not  constitute  any  important  fraction  of 
the  total  nitrogen  of  the  body  or  of  the  feed. 

64.  Alkaloids  and  organic  bases.  —  Alkaloids  are  compara- 
tively rare  in  agricultural  plants,  the  seeds  of  the  lupine  forming 
the   principal   exception.     The   organic   bases,    on   the   other 
hand,  appear  to  be  somewhat  widely  distributed.     In  addition 
to  the  so-called  "  hexon  bases  "  arginin,  lysin  and  histidin,  de- 
rived from  the  proteins  and  nucleo-proteins,  the  bases  cholin, 
betain,  trigonellin  and  stachydrin  have  been  found  in  a  variety 
of  plants. 

65.  Nitrogenous  glucosids.  —  The  substances  of  this  group 
are  characteristic  of  the  vegetable  kingdom.     They  contain 
a  variety  of  nitrogenous  compounds  coupled  with  simple  sugars. 
The  nitrogenous  glucosids  do  not  appear  to  be  especially  abun- 
dant in  the  ordinary  feeding  stuffs  of  domestic  animals  and 
where  they  do  occur  are  distinguished  rather  by  their  specific 
physiological  effects  than  by  their  nutritive  value  in  the  or- 
dinary sense.     E.  Schulze l  mentions  seven  bodies  of  this  class 
which  have  been  found  in  various  plants. 

66.  Amino  acids  and  amids.  —  These  substances  are  by  far 
the  most  abundant  forms  of  non-protein  in  vegetable  materials. 
The  first  one  to  be  discovered  was  asparagin,  in  1805,  in  aspar- 
agus shoots,  and  this  substance  has  since  been  found  in  a  large 
number  of  plants  or  parts  of  plants.     Glutamin,  a  second 
amid,  is  also  of  frequent  occurrence  in  plants. 

1  Jour.  Landw.,  52  (1904),  305. 


38  NUTRITION  OF   FARM  ANIMALS 

Asparagin  and  glutamin  are  respectively  the  amids  of  aspartic  and 
glutamic  acids,  both  of  which  are  constituents  of  the  protein  molecule. 

COOH      COOH      COOH      COOH 

I          I          I          I 
CH2        CH2       CH2        CH2 


CH  •  NH2 

CH  •  NH2 

CH, 

CH2 

1 

1 

1 

1 

COOH 

CO  •  NH2 

CH  •  NH2 

CH- 

Aspartic  acid 

Asparagin 

| 

| 

COOH 

CO- 

Glutamic  acid 

Glut 

It  has  thus  come  about  that  the  term  amids  has  been  more 
or  less  commonly  used  as  a  general  designation  for  the  non-pro- 
tein nitrogenous  substances  found  in  feeding  stuffs.  The  usage, 
however,  is  unfortunate.  The  word  amid  denotes  a  distinct 
class  of  chemical  substances  of  which  only  asparagin  and  glu- 
tamin appear  to  be  especially  common  in  plants,  while  the 
latter  contain  a  variety  of  nitrogenous  substances  which  are 
not  amids  at  all.  The  general  term  non-protein  proposed  above, 
therefore,  seems  preferable. 

In  addition  to  asparagin  and  glutamin  there  have  been  found 
in  feeding  stuffs  a  large  number  of  the  cleavage  products  of  the 
proteins.  E.  Schulze  1>2)3  enumerates  ten  amino  acids,  viz.,  valin, 
leucin,  isoleucin,  phenylalanin,  tyrosin,  prolin,  tryptophan, 
arginin,  lysin  and  histidin,  besides  the  purin  bases  xanthin,  hy- 
poxanthin,  adenin  and  guanin,  as  well  as  guanidin,  allantoin 
and  carnin,  as  having  been  isolated  from  various  vegetable  ma- 
terials. Hart  and  Bentley  4  found  that  from  50  to  70  per  cent 
of  the  water-soluble  nitrogen  of  a  variety  of  feeding  stuffs  ex- 
isted as  amino  acids  or  peptids,  while  the  amid  nitrogen  proper 
amounted  to  only  10  to  20  per  cent. 

Occurrence.  —  These  substances  evidently  stand  in  a  close 
relation  to  the  protein  metabolism  of  the  plant.  They  appear 
to  be  in  part  intermediate  products  in  the  synthesis  of  protein 
from  nitrates  and  ammonium  salts  and  in  part  to  be  formed  in 
the  cleavage  of  proteins  necessary  for  their  translocation  and 
resynthesis  during  the  processes  of  growth.  They  are  especially 

1  Jour.  f.  Landw.,  52  (1904),  305.  2  Ztschr.  Physiol.  Chem.,  45  (1905),  38. 

3  Ztschr.  Physiol.  Chem.,  47  (1906),  507.        4  Jour.  Biol.  Chem.,  22  (1915),  477- 


THE   COMPONENTS  OF  PLANTS  AND   ANIMALS         39 

abundant,  therefore,  where  growth  is  going  on  most  rapidly. 
Young  and  succulent  feeding  stuffs,  such  as  pasture  grass,  green 
soiling  crops  and  the  like,  accordingly  contain  a  considerable 
proportion  of  their  nitrogen  in  the  non-protein  form.  As  plants 
approach  ripeness,  the  proportion  of  non-protein  to  protein 
nitrogen  becomes  less,  so  that  mature  hay,  straw  and  the  like 
are  relatively  poor  in  non-proteins.  This  is  especially  true  of 
seeds,  whose  nitrogen  is  contained  chiefly  in  the  reserve  pro- 
teins, although  small  amounts  of  various  non-proteins  are  also 
found.  One  class  of  feeding  stuffs  relatively  rich  in  non-protein 
is  the  roots  and  tubers,  in  which  the  conversion  of  inorganic 
nitrogen  into  protein  seems  to  be  incomplete  and  in  which  the 
non-protein  serves  as  a  nitrogenous  reserve  for  the  growth  of 
the  succeeding  year.  Finally,  feeding  stuffs  which  have  under- 
gone fermentation,  such  as  silage,  show  a  relative  increase  of  the 
non-protein  nitrogen  over  that  of  the  original  material. 

67.  Nitrates  and  ammonium  salts.  —  Occasionally  somewhat 
considerable  amounts  of  nitrates  or  of  ammonium  compounds 
are  found  in  vegetable  material,  especially  when  the  supply  of 
soluble  nitrogen  compounds  in  the  soil  is  abundant.     In  such 
cases  they  are  to  be  regarded  as  materials  taken  up  in  excess 
of  the  immediate  needs  of  the  plant. 

§  6.    SUNDRY  INGREDIENTS 

68.  Number  and  significance.  —  In  the  foregoing  sections 
the  groups  of  substances  which  constitute  the  animal  body  or, 
in  the  form  of  feed,  supply  the  matter  and  energy  for  its  growth 
and  maintenance  have  been  considered.     It  is  hardly  necessary 
to  say,  however,  that  these  four  groups,  the  carbohydrates, 
fats,  proteins  and  non-proteins,  are  very  far  from  comprising  all 
the  constituents  of  animals  or  plants. 

In  the  animal  body  the  physiological  chemist  has  recognized 
relatively  small  amounts  of  a  vast  number  of  substances  of 
the  most  varied  nature.  Some  of  these  are  derived  quite  di- 
rectly from  the  proteins,  fats  or  carbohydrates  and  these  will  be 
considered  to  a  greater  or  less  extent  in  studying  the  changes 
which  these  substances  undergo  in  the  body.  Others,  while  of 
great  physiological  importance,  have  little  direct  relation  to  the 
processes  of  nutrition. 


40  NUTRITION  OF  FARM  ANIMALS 

Similarly,  plants  contain  a  great  variety  of  ingredients  not 
strictly  belonging  to  any  of  the  four  main  groups.  In  the 
aggregate,  these  substances  do  not  often  add  greatly  to  the  po- 
tential food  value  of  feeding  stuffs,  but,  on  the  other  hand, 
they  may  in  some  cases  considerably  modify  their  palatability 
or  the  activity  of  the  various  processes  of  nutrition  and  so  affect 
the  actual  results  of  feeding.  Until  recently  these  secondary  in- 
gredients of  feeding  stuffs  have  received  comparatively  little 
attention. 

69.  Organic  acids.  —  Aside  from  the  small  amounts  of  free 
fatty  acids  occurring  in  most  native  fats,  both  animal  and  vege- 
table (29,  33),  the  acids  of  this  series  are  seldom  or  never  found 
in  native  feeding  stuffs.     In  those  feeding  stuffs  which  have 
undergone  bacterial  fermentation,  however,  notably  in  the  case 
of  silage,  more  or  less  acetic  and  butyric  acids  occur,  but  the 
principal  acid  product  of  such  fermentations  is  lactic  acid, 
C3H6O3.     The  same  acids,  along  with  formic  and    propionic 
acids  and  minute  amounts  of  ethyl  aldehyde,  likewise  result 
from  the  bacterial  fermentation  of  the  carbohydrates  of  the 
feed  in  the  paunch  of  ruminants  and  thus  constitute  a  not  un- 
important portion  of  the  non-nitrogenous  material  resorbed 
from  the  feed  (128-132).     The  principal  organic  acids  found 
in  native  feeding  stuffs  are  malic,  tartaric,  citric  and  oxalic, 
usually  as  the  potassium,  sodium  or  calcium  salts. 

70.  Ethereal  oils.  —  The  so-called  ethereal  oils  are  substances 
of  complex  molecular  nature,  somewhat  resembling  the  true 
oils  in  their  physical  properties  but  which  can  readily  be  dis- 
tilled in  a  current  of  steam.     Familiar  examples  are  the  so-called 
oils  of  peppermint,  lemon,  anise,  and  the  like.     It  is  not  known 
that  they  have  any  direct  nutritive  value  themselves  but  they 
add  to  the  flavor  and  aroma  of  feeds  and  in  some  cases  are  be- 
lieved  to   stimulate   the   digestive  processes.     The   agreeable 
odor  of  good  hay,  for  example,  and  doubtless  in  part  its  fa- 
vorable dietetic  effect,  is  due  to  substances  resembling  in  prop- 
erties the  ethereal  oils.     To  the  same   class  of   ethereal   oils 
belong  the  oils  of  mustard,  onion  and  garlic,  whose  deleterious 
effect  upon  the  flavor  of  dairy  products  is  so  well  known. 

71.  Flavoring  substances  in  general.  —  What  is  called  the 
flavor  of  a  food  or  feeding  stuff  depends  largely  upon  the  action 
on  the  sense  of  smell  of  a  great  variety  of  substances  either  con- 


THE   COMPONENTS  OF  PLANTS  AND   ANIMALS         41 

tained  in  the  material  originally  or,  especially  in  the  case  of 
human  foods,  artificially  added  or  developed  during  cooking. 
Besides  ethereal  oils,  stock  -feeds  contain  a  great  variety  of 
bitter  or  astringent  substances,  gums,  waxes,  resins,  etc.,  etc., 
of  whose  properties  and  physiological  effects  little  or  nothing  is 
known.  The  flavor  and  palatability  of  feed,  as  already  indi- 
cated, are  usually  dependent  upon  these  accessory  ingredients, 
while  the  fact  that  palatability  is  an  important  factor  in  nu- 
trition aside  from  any  direct  nutritive  effect  will  appear  in  later 
discussions. 

72.  Vitamins:  Growth  substances. —  Much  attention  has 
been  devoted  during  the  past  few  years  to  an  important  but  as 
yet  rather  ill-defined  group  of  food  constituents  called  by  some 
investigators  vitamins  and  by  others  growth  substances.  These 
substances,  however,  are  known  by  their  effects  rather  than  by 
their  chemical  properties  and  may  therefore  be  more  appropri- 
ately considered  in  their  relations  to  the  requirements  for 
maintenance  and  growth  (438,  498,  738). 


CHAPTER  II 

THE  COMPOSITION  OF    ANIMALS  AND  OF    FEEDING  STUFFS 
§  i.    THE  CELL 

73.  Definition.  —  The  cell  may  be  defined  as  the  biological 
unit  of  all  life.     It  is  the  simplest  form  in  which  living  matter 
can  exist.     It  might  be  regarded  as  bearing  somewhat  the  same 
relation  to  the  animal  or  plant  that  the  atom  does  to  a  complex 
organic  molecule  such  as  that  of  one  of  the  proteins  for  example. 
It  is  seen  in  its  simplest  form  in  unicellular  organisms  (protozoa) 
in  which  all  the  functions  of  life  are  performed  by  a  single  cell. 
As  we  ascend  in  the  scale  of  organization  a  number  of  cells  are 
united  to  form  one  individual,  the  various  vital  functions  being 
to  a  greater  or  less  extent  distributed  among  different  cells  or 
cell  groups.     In  the  higher  organisms  the  cells  are  numbered 
by  myriads,  while  the  physiological  division  of  labor  and  the 
corresponding  differentiation  of  form  reach  an  extreme.     The 
organization  of  such  an  individual  has  been  likened  to  that  of 
a  state  or  nation,  in  which  the  functions  of  the  single  citizen 
are  highly  specialized.     A  few  of  the  diverse  forms  of  animal 
cells  are  represented  in  Fig.  i. 

74.  Structure   of  cells.  —  The  typical  cell  consists  of  the 
cell  body,  or  cytoplasm,  within  which  is  the  nucleus.     The 
peripheral  portion  of  the  cytoplasm  is  often  somewhat  more 
compact  than  the  remainder  and  serves  to  separate  the  cell 
from  its  surroundings.     Sometimes  a   distinct   membrane,   or 
cell  wall,  is  developed,  especially  in  plants,  although  this  is  not 
a  necessary  part  of  the  cell.     The  name  protoplasm  is  often 
applied  to  the  entire  active  part  of  the  cell,  i.e.,  to  cytoplasm  plus 
nucleus.     All  forms  of  life,  vegetable  as  well  as  animal,  are  in- 
dissolubly  associated  with  and  manifested  through  the  activities 
of  protoplasm,  which  was  called  by  Huxley  the  physical  basis 
of  life.     It  should  be  understood,  however,  that  the  word  pro- 
toplasm is  not  a  chemical  but  a  biological  term.     It  is  a  struc- 

42 


COMPOSITION  OF  ANIMALS  AND   OF  FEEDING  STUFFS    43 

ture  rather  than  a  substance.  Moreover,  there  is  not  one  pro- 
toplasm, common  to  all  cells,  but  as  many  protoplasms  as  there 
are  kinds  of  cells. 

There  is  a  more  or  less  sharp  differentiation  between  the 
functions  of  the  nucleus  and  those  of  the  cytoplasm.  The 
nucleus  appears  to  be  especially  concerned  in  cell  reproduction, 


FIG.  i.  —  Different  types  of  cell  composing  the  body.     (Hadley,  The  Horse 
in  Health  and  Disease.) 

the  formation  of  a  new  cell  beginning  with  a  division  of  the 
nucleus  of  an  existing  cell  and  being  followed  by  a  division 
of  its  cytoplasm.  The  main  function  of  the  cytoplasm,  on 
the  other  hand,  seems  to  be  the  nutrition  of  the  cell,  and  the 
presence  of  at  least  a  minimum  amount  of  it  is  essential  to  the 
continued  existence  of  the  nucleus.  For  the  present  purpose, 
it  is  unnecessary  to  attempt  a  further  discussion  of  those  finer 
details  of  the  structure  of  the  cell  which  have  been  worked  out 
by  the  labors  of  the  histologist  and  physiologist. 


44  NUTRITION  OF  FARM  ANIMALS 

75.  Composition  of  protoplasm.  —  The  chemical  constitution 
of  living  protoplasm  is  unknown,  partly  because  it  is  undoubtedly 
very  complex  but  chiefly  because  of  its  instability  and  the  im- 
possibility of  isolating  it  without  at  the  same  time  destroying 
its  life.     Moreover,  it  doubtless  varies  materially  in  cells  of 
different  types.     The  proteins,  perhaps  combined  with  each 
other    into    "  giant    molecules,"    undoubtedly    constitute    the 
basis  and  predominating  ingredient  of  protoplasm,  but  certain 
lipoids  (lecithins  and  cholesterins),  ash  ingredients  (electrolytes), 
and  perhaps  glycogen  and  other  carbohydrates,  in  addition, 
of  course,  to  water,  appear  to  be  also  essential  constituents.     In 
the  cytoplasm,  the  simple  proteins  (41)  seem  to  predominate, 
while  the  nucleus  is  especially  characterized  by  the  presence  of 
the  nucleoproteins  (52). 

76.  The  cell  wall.  —  As  already  indicated,  the  protoplasm 
often  develops  a  cell  wall.     So  far  as  concerns  the  species  of 
plants  which  serve  as  feed  for  farm  animals,  it  may  be  said 
that  a  vegetable  cell  is  always  surrounded  by  a  cell  wall  the 
basic  ingredient  of  which  is  the  carbohydrate  cellulose,  a  sub- 
stance not  found  in  the  bodies  of  the  higher  animals. 

In  the  young  and  growing  parts  of  plants,  the  cell  wall  is  thin 
and  consists  substantially  of  cellulose  only.  In  certain  parts 
of  plants,  such  as  the  cotyledons  and  endosperms  of  seeds  or 
the  tissues  of  succulent  roots  and  tubers,  the  cell  wall  remains 
comparatively  thin  even  in  mature  tissue.  In  other  parts  of 
the  plant,  on  the  contrary,  it  becomes  very  much  thickened  by 
the  deposition  of  additional  cellulose  and  especially  of  substances 
other  than  cellulose.  These  other  substances,  which  appear 
to  be  essentially  carbohydrates  or  their  derivatives,  are  of  two 
general  kinds.  The  first  of  these  is  the  hemicelluloses  (18), 
which  are  more  readily  attacked  by  hydrolyzing  agents  than 
pure  cellulose  and  which  constitute  to  a  large  extent  a  deposit 
of  reserve  material  and  include  both  hexosans  and  pentosans. 
The  second  consists  of  substances  belonging  to  the  lignin  and 
cutin  groups  (19,  20),  which  serve  to  impart  strength  and  rigidity 
along  with  more  or  less  impermeability  to  the  cell  wall.  They 
are,  therefore,  particularly  abundant  in  older  plants  as  com- 
pared with  younger  ones  and  in  those  organs  which  serve  to 
support  the  plant,  such  as  the  stem.  The  extreme  form  of  the 
thickened  cell  wall  is  seen  in  wood.  A  few  of  the  numerous 


COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS    45 

forms   of    vegetable   cells  are   illustrated   in   Figs.  43-45   of 
Chapter  XV. 

77.  Cell  enclosures.  —  In  addition  to  the  essential  constitu- 
ents of  the  cytoplasm  and  nucleus  there  are  observed  in  cells 
a  variety  of  other  substances  designated  as  subsidiary  ingredi- 
ents or  cell  enclosures.     These  may  consist  of  food  material 
which  has  entered  the  cell  and  is  on  its  way  to  being  incor- 
porated into  the  molecules  of  protoplasm,  or,  on  the  other  hand, 
of  waste  products  of  cell  activity  on  their  way  to  being  ex- 
creted from  the  cell  into  the  surrounding  medium.     Moreover, 
many  cells  have  the  power  of  storing  up  surplus  food,  especially 
non-nitrogenous  substances,  as  reserve  material.     Such  material 
is  not  usually  regarded  as  constituting  a  part  of  the  protoplasm 
but  as  being  simply  included  in  it  mechanically. 

The  most  common  cell  enclosure  in  the  animal  is  fat,  which 
is  contained  in  large  quantity  in  certain  connective  tissue  cells 
and  constitutes  the  reserve  fuel  material  of  the  animal  body, 
the  storage  of  carbohydrates  (glycogen)  being  much  more 
limited  in  amount.  While  some  important  groups  of  plants 
also  store  up  large  amounts  of  fat  in  their  seeds,  nevertheless 
the  predominating  reserve  materials  in  the  vegetable  kingdom 
are  carbohydrates,  including  the  reserve  carbohydrates  of  the 
cell  wall  and,  as  a  cell  enclosure,  starch.  Starch  is  found  in 
all  parts  of  plants,  but  is  especially  abundant  in  seeds  and  in 
the  starchy  roots  and  tubers,  where  large  amounts  of  this  sub- 
stance are  stored  up.  Illustrations  of  plant  cells  containing 
starch  are  afforded  by  Figs.  43-45  of  Chapter  XV. 

Both  because  of  the  chemical  composition  of  the  cell  wall 
and  the  nature  of  the  cell  enclosures,  carbohydrates  are  quan- 
titatively the  predominating  ingredients  of  most  plants,  while 
animal  cells  and  tissues  are  chiefly  proteid  or  fatty  in  character. 

§  2.  ANIMAL  TISSUES  AND  ORGANS 

78.  Classification.  —  Not  only  do  the  cells  of  higher  animals 
show  extreme  differentiation  of  form  and  function,  but  cells 
having  the  same  general  nature  and  office  are  associated  together 
to  form  what  are  called  tissues,  such  as  nerve  tissue,  muscular 
tissue,  connective  tissue  and  the  like,  each  serving  its  own 
specific  purpose.    These  tissues,  again,  are  grouped  together 


46  NUTRITION  OF  FARM  AMIMALS 

to  form  organs,  such  as  the  muscles,  heart,  lungs,  stomach, 
liver  and  the  like,  each  performing  its  special  part  in  the  com- 
plex interplay  of  activities  necessary  for  the  life  of  the  organism 
as  a  whole. 

Since  this  is  not  a  treatise  on  anatomy,  it  is  unnecessary  to 
consider  in  detail  all  the  diverse  types  of  tissue  or  all  the  various 
organs  making  up  the  body.  It  is  desirable,  however,  that  the 
student  of  nutrition  should  acquire  some  notion  of  the  chemical 
make-up  of  the  various  parts  of  the  body.  For  this  purpose  it 
will  be  convenient  to  use  the  following  scheme,  based  chiefly 
on  the  functions  performed  by  the  different  groups  of  tissues, 
which  ignores  to  some  extent  the  distinction  between  tissues 
and  organs  and  which  does  not  pretend  to  be  an  exact  or  ex- 
haustive classification. 

First :  The  supporting  tissues,  including  bone,  tendon,  carti- 
lage, ligament,  elastic  tissue,  etc. 

Second :  The  tissues  of  motion,  including  the  muscular 
tissues  and  the  nerve  tissues  or  the  nervous  system. 

Third :  The  tissues  of  alimentation,  including  the  tissues 
and  organs  concerned  in  digestion,  resorption,  circulation, 
respiration  and  excretion. 

Fourth  :  The  epidermal'  tissues. 

Fifth :  The  reserve  tissues,  including,  besides  adipose 
tissue,  those  tissues  in  which  glycogen  is  more  or  less  abun- 
dantly stored. 

The  supporting  tissues 

79.  Intercellular  substance.  —  In  the  bodies  of  the  higher 
animals  certain  tissues  show  an  enormous  development  of  the 
so-called  intercellular  substance,  so  that  the  cells,  instead  of 
closely  adjoining  each  other,  are  imbedded  in  a  mass  of  non- 
cellular  material  which  may  vary  greatly  in  consistency.  Some- 
times this  intercellular  substance  is  entirely  homogeneous  but 
it  usually  contains  a  greater  or  less  number  of  fibers  imbedded  in 
a  homogeneous  basis.  By  virtue  of  the  special  properties  of 
the  intercellular  substance,  tissues  of  this  sort  perform  pri- 
marily mechanical  functions,  maintaining  the  form  of  the  body 
or  serving  to  connect  and  support  other  tissues,  while  the  cells 
themselves  serve  principally  to  produce  and  maintain  the  inter- 
cellular substance.  The  organic  basis  of  the  latter  is  the  group 


COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS      47 

of  proteins  called  in  Chapter  I  the  albuminoids  or  the  sclero- 
proteins  (51  e)  accompanied  by  varying  amounts  of  mineral 
matter,  and,  of  course,  a  considerable  proportion  of  water. 

80.  Bone.  —  Bone  is  the  most  familiar  example  of  the  sup- 
porting tissues  of  the  animal  body.  In  the  young  embryo  the 
bones  first  appear  as  cartilaginous  structures  consisting  of 
rounded  cells  imbedded  in  a  homogeneous  intercellular  substance 
containing  also  fibers  and  consisting  mainly  of  collagen  (51  e). 
As  development  advances,  the  process  of  ossification  begins,  the 
homogeneous  substance  of  the  cartilage  taking  up  inorganic  salts, 
chiefly  calcium  phosphate,  while  the  fibers  of  the  cartilage  are 
stated  not  to  take  part  in  this  process.  In  addition  to  mineral 
matter,  the  bones  store  up  also  a  variable  amount  of  fat.  Ma- 
ture bone,  therefore,  aside  from  its  fat,  consists  of  a  basis  of 
organic  matter  largely  impregnated  with  mineral  matter.  The 
presence  of  these  two  classes  of  constituents  is  readily  demon- 
strated by  the  familiar  experiments  in  which,  on  the  one  hand, 
the  mineral  matter  is  removed  by  immersion  in  dilute  acid 
leaving  behind  the  flexible  cartilage,  or,  on  the  other  hand, 
the  organic  basis  of  the  bone  is  destroyed  by  heating,  leaving 
the  so-called  bone  ash. 

Ossification  has  not  been  completed  at  birth  but  continues  to  a 
greater  or  less  extent  up  to  full  maturity  Moreover,  it  is  not  carried 
to  the  same  extent  in  all  bones  nor  in  different  parts  of  the  same  bone. 
Consequently,  both  the  percentages  of  ash  and  of  fat  and  the  propor- 
tion of  water  to  dry  matter  in  bones  may  vary  within  wide  limits,  so 
that  it  is  impossible  to  state  an  average  composition.  The  extremes 
of  1 5  per  cent  and  44  per  cent  have  been  found  for  the  average  water 
content  of  the  entire  skeleton  of  the  dog  and  even  wider  variations 
have  been  reported  in  the  case  of  man.  Compact  bones  contain  less 
water  than  more  spongy  ones. 

In  general  it  may  be  said  that  from  one-half  to  two-thirds  of 
the  dry,  fat-free  bone  consists  of  ash.  About  three-fourths  of 
the  remainder  is  stated  to  consist  essentially  of  albuminoids,  or 
collagens,  yielding  gelatin  when  treated  with  hot  water,  es- 
pecially under  pressure.  It  is  evident,  therefore,  that  the 
skeleton  of  an  animal  contains  not  only  a  large  share  of  the 
total  ash  of  the  body  but  a  not  inconsiderable  portion  of  its 
nitrogenous  constituents  as  well.  On  the  average  of  the  ten 
animals  analyzed  by  Lawes  and  Gilbert  (97),  77.78  per  cent  of 


48 


NUTRITION  OF  FARM  ANIMALS 


the  total  ash  of  the  entire  animal  and  83.01  per  cent  of  the  ash 
of  the  carcass  was  contained  in  the  bones.  Of  the  total  nitro- 
gen of  the  carcasses  of  eight  of  these  animals  18.04  Per  cent 
was  contained  in  the  bones.  Corresponding  data  for  the  entire 
animal  are  not  recorded. 

81.  Bone  ash.  —  But  while  the  composition  of  bone  itself 
is  quite  variable,  that  of  the  bone  ash  is  notably  constant  even  in 
different  species.  The  predominant  ingredient  is  tri-calcic 
phosphate  but  it  contains,  also,  calcium  carbonate  as  well  as 
phosphates  and  carbonates  of  magnesium  and  other  bases. 
The  average  composition  given  by  Zalesky  1  is  as  follows  :  — 

TABLE  5. — COMPOSITION  OF  BONE  ASH  OF  DIFFERENT  SPECIES 


MAN 

CATTLE 

GUINEA  PIG 

TURTLE 

Calcium  phosphate      .... 

83-89 

86.09 

87.32 

85.98 

Magnesium  phosphate     .     .     . 

1.04 

1.  02 

1.05 

1.36 

Calcium    combined   with  CO2, 

Cl,  Fl     

7  6< 

7  36 

7  O3 

6  32 

Carbon  dioxid    . 

573 

6  20 

507 

More  detailed  analyses  by  Gabriel2  yielded  the   following 
results :  — 

TABLE  6.  —  COMPOSITION  OF  BONE  ASH 


TEETH  OF 
CATTLE 

BONES  OF 

MAN 

BONES  OF 
CATTLE 

BONES  OF 
GEESE 

CaO    
MgO  . 

% 
50.76 

I  C2 

% 
5L31 

O  77 

% 
51.28 

I  OZ 

% 
51.01 

I  27 

K2O    
Na2O 

O.2O 
I  l6 

0.32 
I  OA 

0.18 

I  OQ 

O.I9 
I  II 

H2O    . 

221 

2  4.6 

2  33 

3.O1? 

P2O5   

3888 

36  6s 

37.46 

38.19 

CO2 

A  OQ 

5  86 

e  06 

4.  II 

Cl  

0.05 

O.OI 

O.O4 

0.06 

98.87 

98.43 

98.49 

98.99 

1  Neumeister;  Lehrbuch  der  Physiologischen  Chemie,  1897,  p.  456. 
2Ztschr.  Physiol.  Chem.,  18  (1894),  257. 


COMPOSITION  OF  ANIMALS  AND  OF   FEEDING  STUFFS      49 

The  small  amounts  of  magnesium,  sodium,  potassium,  carbon 
dioxid  and  chlorin  appear  to  be  as  essential  ingredients  of  bone 
ash  as  its  calcium  or  phosphorus. 

82.  Cartilage,    ligament,  tendon,  elastic    tissue.  —  Not    all 
of    the    cartilaginous    ground    work    of  the    skeleton    as    laid 
down  in  the  embryo  is  converted  into  bone.     In  particular,  the 
end  surfaces  of  bones  at  a  joint  consist  of  cartilage,  which  in 
other  cases  forms  a  connecting  link  between  adjoining  bones, 
as,  for  example,   the  cartilage  connecting  the  ribs  with  the 
breast  bone,  thus  allowing  a  limited  degree  of  motion.     At  the 
joints  proper,  the  bones  are  held  in  place,  and  the  direction  and 
extent  of  their  motions  limited,  by  the  ligaments,  while  the 
muscles  which  serve  to  impart  motion  to  the  various  parts  of 
the  body  are  attached  to  the  bones  by  means  of  tendons.     In 
many  cases  the  intercellular  substance  of  the  supporting  tissue 
contains  fibers  of  elastin.     When  these  fibers  are  abundant  the 
tissue  is  elastic  in  contrast  to  the  ligaments  and  tendons  of  the 
joints,  which  are  almost  inextensible.     A  striking  instance  is 
afforded  by  the  elastic  band  (Ligamentum  mtchce)  which  runs 
along  the  back  of  the  neck  of  quadrupeds  and  supports  the 
weight  of  the  head.     Another  example  is  furnished  by  the  layer 
of  elastic  tissue  contained  in  the  walls  of  the  arteries   which 
gives  them  a  certain  degree  of  resilience  to  the  pressure  of  the 
blood  pumped  by  the  heart. 

The  "  organic  "  portion  of  all  these  forms  of  supporting  tis- 
sue, like  the  organic  portion  of  the  bones,  consists  essentially  of 
different  proteins  belonging  to  the  group  of  albuminoids. 

83.  Connective  tissue.  —  This  name  is    sometimes    applied 
to  all  the  various  forms  of  supporting  tissue,  since  they  also 
serve  to  connect  the  various  organs  of  the  body.     In  a  more 
ordinary  and  limited  sense,  however,  it  is  used  to  designate  a 
form  of  supporting  tissue  of  which  the  most  familiar  example 
is  the  tissue  lying  between  the  skin  and  the  underlying  muscles, 
or  lean  meat,  and  serving  to  connect  them  together.     A  more 
careful  examination  shows  that  this  subcutaneous  connective 
tissue  is  continuous  with  other  similar  tissue  which   extends 
between  the  single  muscles  and  serves  at  the  same  time  to  de- 
limit them  and  connect  them.     Not  only  so,  but  this  sheath 
of  connective  tissue  extends  into  the  muscle  itself,  dividing  it 
into  muscular  bundles  or  fasciculi  and  these  again  into  secondary 


50  NUTRITION  OF   FARM   ANIMALS 

fasciculi.  The  connective  tissue  of  the  interior  of  the  muscle 
unites  at  the  ends  and  is  continuous  with  a  form  of  connective 
tissue  already  mentioned,  viz.,  the  tendons,  by 
means  of  which  the  muscles  are  attached  to  the 
bones  (Fig.  2). 

A  similar  sheath  of  connective  tissue  surrounds 
the  internal  organs  of  the  body  and  extends  into 
them,  forming  a  framework  which  supports  the 
active  tissues  of  these  organs  as  well  as  the  blood 
vessels,  nerves,  lymphatics,  etc.,  so  that  it  may  be 
said  in  a  broad  general  way  that  the  body  of  a 
higher  animal  consists  of  a  variety  of  active  tissues 
and  organs  contained  in  and  supported  by  connec- 
One  end  of  a  tive  tissue  and  the  other  forms  of  supporting  tissue 


d  already  described. 
s  e  d  g  w  i  c  k,  Like  other  forms  of  supporting  tissue,  the  connec- 
The  Human  tive  tissue  consists  of  cells  which  have  produced  a 
relatively  large  amount  of  intercellular  substance, 
which  in  connective  tissue  consists  chiefly  of  fibers.  Chem- 
ically, it  is  composed  of  collagen.  Cells  of  connective  tissue, 
however,  may  also  store  up  within  themselves  large  amounts 
of  fat  (94). 

Tissues  of  motion 

84.  The  muscles.  —  Both  the  external  movements  of  an 
animal  and  those  of  the  internal  organs  are  effected  by  means 
of  the  muscles,  and  the  muscular  tissue  is  preeminently  the 
tissue  of  motion.     Moreover,  the  muscles  make  up  a  large  part 
of  the  entire  mass  of  the  body  of  a  lean  animal  and  furnish 
nearly  all  the  protein  contained  in  the  edible  portion  of  the 
carcass.     The  composition  of  muscle  and  muscular  tissue,  there- 
fore, is  of  special  interest. 

85.  Structure  of  muscles.  —  The  smallest  anatomical  element  of 
muscular  tissue  is  the  single  muscle  fiber.     This  is  a  highly  specialized 
and  greatly  elongated,  thread-like  cell  one  to  one  and  a  half  inches 
long  and  having  a  diameter  of  from  .0004  to  .004  inch.     It  is  en- 
closed in  a  very  thin  transparent  membrane  and  contains  many 
nuclei.     A  large  number  of  these  fibers  —  hundreds  or  even  thousands 
—  are  bound  together  to  form  a  fasciculus,  the  fibers  running  length- 
wise and  overlapping  each  other,  being  generally  shorter  than  the 


COMPOSITION  OF  ANIMALS  AND   OF   FEEDING   STUFFS      51 


fasciculus.  These  fasciculi,  as  stated  in  a  previous  paragraph  (83), 
are  surrounded  by  connective  tissue  and  united  into  larger  fasciculi, 
or  bundles,  each  with  its  envelope  of  connective  tissue,  these  bundles 
again  being  united  to  form  the  individual  muscles.  The  connective 
tissue  serves  also  to  carry  the  blood  vessels,  nerves  and  lymphatics 
with  which  the  muscle  is  abundantly  supplied,  and,  moreover,  may 
contain  larger  or  smaller  accumulations  of  fat. 
Evidently,  then,  the  muscle  as  a  whole,  and 
even  more  the  collective  muscles  making  up 
the  lean  meat  of  an  animal,  are  far  from  consti- 
tuting a  homogeneous  material. 

86.  Composition  of  muscles.  —  If  the 
term  muscular  tissue  be  limited  to  the 
ultimate  muscular  fibers  which  are  the  ac- 
tive agents  in  producing  motion,  consider- 
ing the  other  structural  elements  of  the 
muscle  as  accessory,  it  may  probably  be 
said  in  a  general  way  that  it  consists  essen- 
tially of  water,  protein,  meat  extractives 
and  the  various  lipoids  and  electrolytes 
found  in  greater  or  less  amounts  in  all 
protoplasm.  But  such  a  limitation  of  the 
term  muscular  tissue,  however  rational  from 
an  anatomical  standpoint,  is  little  suited 
to  the  present  purpose.  In  the  nutrition  muscle  fiber. 
of  the  animal,  material  is  required  to  build 
up  the  entire  muscular  system,  with  all 
its  accessory  structures,  and  not  merely  for  the  production  of 
the  muscle  fibers,  and  we  are  concerned,  therefore,  with  the 
composition  of  the  muscles  as  a  whole  —  i.e.,  of  the  lean  meat  — 
rather  than  with  that  of  the  ultimate  muscle-fibers. 

Since,  however,  the  lean  meat  contains  a  variety  of  tissues 
aside  from  muscular  tissue  in  the  narrower  sense  —  connective 
tissue,  nerves,  blood  and  lymph  vessels,  etc.  (85),  with  more  or 
less  of  the  fluid  contents  of  the  latter  —  it  is  evident  that  its 
composition  is  likely  to  be  variable.  Moreover,  the  lean  meat, 
especially  of  fat  animals,  contains  a  considerable  and  variable 
amount  of  fat  even  after  all  the  fat  tissue  which  it  is  practicable 
to  separate  mechanically  has  been  removed.  This  fat,  how- 
ever, forms  no  part  of  the  muscle  proper  but  is  simply  a  deposit 


FIG.   3.  — Part    of    a 
(Hough 


NUTRITION  OF  FARM  ANIMALS 


of  reserve  material.  It  is  contained  in  minute  masses  of  adipose 
tissue  (94)  developed  between  the  muscle  bundles  or  even 
between  the  individual  muscular  fibers  and  differing  only  in 
size  from  the  larger  masses  which  may  be  trimmed  off  or  re- 
moved with  the  scalpel.  It  is  necessary  to  distinguish,  there- 
fore, between  lean  meat  in  the  commercial  sense,  with  its  vary- 
ing content  of  fat,  and  lean  meat  in  the  stricter  scientific  sense, 

i.e.,  the  fat-free  muscle.     The  com- 
position of  the  latter  may  be  ascer- 
tained either  by  actually  removing 
the  fat  from  the  ordinary  trimmed 
meat   by  means   of   a  solvent   and 
analyzing  the  residue  or,  more  con- 
veniently,   by    analyzing    the    fresh 
meat  and  removing  the  fat  arithmet- 
ically, i.e.,  by  calculating  the  com- 
position of  the  fat-free  muscle. 
87.   Composition  of  fat-free  muscle. 
-The   composition  of  the  fat-free 
lean  meat  of  butchers'  cuts  has  been 
determined  by  Henneberg,  Kern  and 
Wattenberg1  for  two  old  sheep  and 
FIG.  4.  —  Fat  cells  in  muscle,    six  younger  ones  ranging  from  6|  to 
(Bailey's  Cyclopedia  of  Ameri-    2g  months  old,  and  Jordan2  has  de- 
can  Agriculture.)  ,   ,,  ...  ,.  , ,      , 

termmed  the  composition  of  the  lean 
meat  of  the  entire  carcasses  of  four  steers. 


TABLE  7.  —  AVERAGE  COMPOSITION  OF  FAT-FREE  LEAN  MEAT  OF  SHEEP 


OLD  SHEEP 

LAMBS 

AVERAGE 
OF  ALL 

No.  8 
Lean 

No.  8 
Very 
fat 

6| 
mos. 
old 

13 
mos. 
old 

22 

mos. 
old 

28 

mos. 
old 
Fat 

13 

mos. 
old 
Fat 

18 
mos. 
old 
Fat 

Water     
Insoluble  protein 
Soluble  protein     .     . 
Meat  extractives  .     . 
Ash    

79.41 
15-85 
1.29 
2.18 
1.27 

79.02 
15-73 
1-93 
2.17 
I-I5 

81.01 
14.89 
1.56 
1.44 

1.  10 

80.35 
15-12 
1.72 
1.74 
1.07 

79-35 
15-74 
1-63 
2.14 
1.14 

78.60 
15.90 
1.90 
2.40 
i.  20 

80.21 
14.86 
2.16 
1.66 
i.  ii 

79.17 
15-65 
2.16 
1.84 
1.18 

79.64 
I5-47-) 
1.79  U9-2I 
1-95  J 
i.  IS 

100.00 

100.00 

100.00 

IOO.OO 

100.00 

100.00 

100.00 

100.00 

IOO.OO 

1  Jour.  Landw.,  26  (1878),  549;   28  (1881),  289. 

2  Maine  Expt.  Sta.  Rpt.  1895,  II,  36. 


COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS      53 
TABLE  8.  —  AVERAGE  COMPOSITION  OF  FAT-FREE  LEAN  MEAT  OF  STEERS 


22  Mos.  OLD 

32  Mos.  OLD 

AVERAGE 
OF  ALL 

No.  i 

No.  4 

No.  2 

No.  3 

Water         

77.61 

21.37 
1.  02 

76.60 
22.30 

I.IO 

78.01 

20.94 
1.05 

77.18 

21.77 
1.05 

77-35 

21.60 
1.05 

Total  nitrogenous  matter  (by 
difference)    
Ash    

IOO.OO 

100.00 

100.00 

IOO.OO 

IOO.OO 

The  figures  of  the  foregoing  tables  indicate  but  very  slight 
differences  in  the  composition  of  the  fat-free  lean  meat  of  the 
different  animals,  aside  from  a  slightly  greater  water  content 
in  that  of  the  sheep.  An  approximate  average  is  95  per  cent  total 
nitrogenous  matter  and  5  per  cent  ash  in  the  dry,  fat-free  sub- 
stance. 

In  the  course  of  investigations  upon  human  nutrition,  nu- 
merous analyses  have  been  made  of  the  various  commercial  cuts 
of  meat  which  in  general  confirm  the  foregoing  figures  and 
show  relatively  small  differences  in  this  respect  between  the 
different  cuts. 

88.  Elementary  composition  of  fat-free  meat.  —  The  fol- 
lowing analyses  by  Rubner,  Stohmann  and  Langbein,  and  Ar- 
gutinsky  show  the  ultimate  composition  of  ash-free  muscular 
tissue  after  prolonged  extraction  with  ether :  — 

TABLE  9.  —  COMPOSITION  OF  FAT-  AND  ASH-FREE  MUSCULAR  TISSUE 


CARBON 

HYDRO- 
GEN 

NITRO- 
GEN 

OXYGEN 

HEAT  OF 
COMBUSTION 

&f 

(y 

PER  GRAM. 

% 

% 

CALS. 

Rubner 

e  -i  AQ 

16  30 

6  61 

Stohmann  and  Langbein  . 

52.02 

7-30 

16.36 

24.32 

5.6409 

Argutinsky 

r  2  it 

7  "?O 

16  15 

24  22 

Kohler J  has  investigated  the  elementary  composition  of  the 
muscular  tissue  of  cattle,  sheep,  swine,  horses,  rabbits  and 
hens.  The  material  was  prepared  with  much  care,  the  fat  being 

1  Ztschr.  Physiol.  Chem.,  31  (1901),  479. 


54 


NUTRITION  OF   FARM   ANIMALS 


removed  as  fully  as  possible  by  prolonged  extraction  with 
ether.  The  residual  fat  which  cannot  be  removed  in  this  way 
was  determined  by  Dornmeyer's  digestion  method  and  a  cor- 
responding correction  made  in  the  analytical  results.  The  fol- 
lowing are  his  averages  for  the  fat-  and  ash-free  substance:  — 

TABLE  10.  —  COMPOSITION  or  FAT-  AND  ASH-FREE  LEAN  MEAT 


HEAT  OF 

No. 
OF  SAM- 

CARBON 

HYDRO- 
GEN 

NITRO- 
GEN 

SULPHUR 

OXYGEN 

COMBUS- 
TION PER 

PLES 

% 

°7 

cy 

% 

% 

GRAM. 

CALS. 

Cattle  .... 

4 

7  14. 

16  67 

0^2 

22   12 

c  6776 

Sheep   

52.53 

7.19 

16.64 

0.69 

22.96 

5-6387 

Swine 

2 

r  2  71 

717 

1  6  60 

o  ^o 

22  95 

r  67^8 

Horse   

3 

52.64 

7.10 

15-55 

0.64 

24.08 

5-5990 

Rabbit      .... 

2 

52.83 

7.10 

16.90 

— 

— 

5.6l66 

Hen      .     . 

2 

<2   36 

6  QO 

16  88 

o  50 

23  28 

5  6173 

All  the  samples  were  tested  for  glycogen,  but  only  traces 
were  found,  except  in  the  horseflesh,  for  the  two  samples  of 
which  an  average  of  3.65  per  cent  was  obtained,  a  result  which 
accounts  for  the  low  figure  for  nitrogen. 


The  tissues  of  alimentation 

89.  Definition.  —  Under  this  heading  may  be  grouped  the 
organs  and  tissues  directly  concerned  with  supplying  food  to 
the  organism,  with  its  distribution  through  the  body,  and  with 
the  removal  of  waste  products  of  cell  activity.  That  is,  it  in- 
cludes the  organs  of  digestion,  resorption,  circulation,  respira- 
tion and  excretion,  which  constitute  what  are  ordinarily  spoken 
of  as  the  entrails  of  slaughtered  animals.  So  far  as  most  of  the 
familiar  internal  organs  of  the  animal  are  concerned  they  may 
be  considered  as  made  up  to  a  large  extent  of  the  classes  of  tis- 
sues already  considered.  In  addition,  however,  the  internal 
organs  include  a  somewhat  distinct  type  of  tissue,  viz.,  glandu- 
lar tissue,  which  plays  an  especially  important  part  in  the  di- 
gestive processes,  while  it  is  also  of  the  highest  significance  for 
other  bodily  functions. 


COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS     55 

Glands,  like  many  other  organs,  have  as  their  basis  a  rather  loose 
and  soft  framework  of  connective  tissue  serving  to  support  cells 
whose  function  it  is  to  prepare  certain  fluids  or  chemical  substances 
required  in  the  body.  The  largest  gland  is  the  liver,  which  secretes 
the  bile  and  has  other  important  functions.  Other  examples  are  the 
pancreas,  spleen,  salivary  glands,  etc.  Less  conspicuous  but  equally 
important  are  the  smaller  glands  imbedded  in  the  walls  of  the  stomach 
and  intestines  which  secrete  such  important  fluids  as  the  gastric 
juice,  intestinal  juices,  etc. 

90.  Chemical  composition.  —  From  the  standpoint  of  hu- 
man nutrition,  the  tissues  of  alimentation  of  farm  animals,  as 
here  broadly  denned,  are  largely  waste  products.  While  cer- 
tain organs,  like  the  liver,  kidneys,  heart,  etc.,  are  utilized  as 
food,  the  larger  portion  of  the  entrails  passes  into  the  offal  and 
the  feed  consumed  in  its  growth  and  maintenance  is  a  part  of 
the  necessary  cost  of  production  of  animal  foods. 

An  idea  of  the  composition  of  the  offal  and  of  the  proportion 
of  total  protein,  fat  and  ash  of  the  body  which  it  contains  is 
afforded  by  Lawes  and  Gilbert's  analyses  of  entire  animals  (97), 
although  the  offal  in  their  experiments  included,  in  the  case  of 
cattle  and  sheep  (but  not  of  pigs) ,  the  head,  feet  and  skin,  while 
the  kidneys  and  kidney  fat  were  in  all  cases  included  in  the 
carcass.  On  the  average  of  the  ten  animals  the  percentage 
composition  of  the  carcass  and  of  the  offal  was :  — 


TABLE  n.  —  COMPOSITION  OF  CARCASS  AND  OFFAL 


CARCASS 

% 

OFFAL 

% 

In  the  fresh  state 
Water      ... 

4.8  4. 

58  8 

Ash     

?  7 

-i  o 

I?  er 

17.2 

Fat      

-3A    A 

21  O 

In  the  fat-free  dry  matter 
Ash 

IOO.O 
21   C 

IOO.O 
14.  0 

Nitrogenous  matter  

78.S 

8S.I 

IOO.O 

IOO.O 

NUTRITION  OF   FARM   ANIMALS 


TABLE  12. —  PERCENTAGE  DISTRIBUTION  OF  ASH,  PROTEIN  AND  FAT 
BETWEEN  CARCASS  AND  OFFAL 


ASH 

PROTEIN 
(NX  6.25) 

FAT 

Fat  calf 
In  carcass      

73.2 

6^.0 

70.  c 

In  offal     

26.8 

34-i 

29-5 

Half  -fat  ox 
In  carcass      
In  offal     

100.0 

77-3 
22.7 

IOO.O 

66.8 
33.2 

IOO.O 

78.1 

21.9 

Fat  ox 
In  carcass      
In  offal 

IOO.O 

77.0 

23  O 

IOO.O 

67.2 

32  8 

IOO.O 

77.0 

23  O 

Fat  lamb 
In  carcass 

IOO.O 
7-1  o 

IOO.O 
^2  I 

IOO.O 

78  I 

In  offal 

26  o 

4.7  O 

21  O 

Store  sheep 
In  carcass 

IOO.O 

73  ^ 

IOO.O 
<C2  8 

IOO.O 
67  2 

In  offal 

26  ^ 

4.7  2 

32  8 

Half-fat  old  sheep 
In  carcass      •    . 

IOO.O 

60  8 

IOO.O 
<4.3 

IOO.O 
72.O 

In  offal     

^O  2 

4C.  7 

28.O 

Fat  sheep 
In  carcass      
In  offal     

IOO.O 

70.5 
29-5 

IOO.O 

52.5 

47-5 

IOO.O 

73-5 
26.5 

Extra-fat  sheep 
In  carcass 

IOO.O 
60  2 

IOO.O 

^o  o 

IOO.O 
7?  Q 

In  offal     

39-8 

50.0 

24.1 

Store  pig 
In  carcass 

IOO.O 

64  o 

IOO.O 
60  4. 

IOO.O 
80  3 

In  offal     

36.0 

30.6 

19.7 

Fat  pig 
In  carcass      
In  offal     .     . 

IOO.O 

64.4 

3<;  6 

IOO.O 

74.0 

26  o 

IOO.O 

89.3 
IO  7 

Mean  of  all 
In  carcass      
In  offal      .     . 

IOO.O 

71.4 
28.6 

IOO.O 

60.8 

39-2 

IOO.O 

77.2 

22.8 

IOO.O 

IOO.O 

IOO.O 

COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS     57 


It  thus  appears  that  the  offal  contained  relatively  more  pro- 
tein and  water  and  less  ash  and  fat  than  the  carcass.  From  the 
weights  of  the  carcass  and  offal,  respectively,  may  be  computed 
the  percentage  distribution  of  the  ingredients  between  the  two 
with  the  results  shown  in  Table  12,  from  which  it  appears 
that  on  the  average  39  per  cent  of  the  protein,  28  per  cent  of 
the  ash  and  23  per  cent  of  the  fat  of  the  entire  animal  was 
contained  in  the  offal. 

Epidermal  tissues 

91.  Functions.  —  The  epidermis,  or  outer,  layer  of  the  skin, 
consists  of  numerous  layers  of  cells  of  which  those  nearer  the 
true  skin  are  alive  and  capable  of  multiplication  while  towards 
the  outer  surface  they  are  gradually  transformed  to  flattened, 
horny  scales  which  serve  as  a  protective  layer  and  gradually 
slough  off.     Both  the  epidermis  and  the  protective  covering  of 
animals,  —  hair,  wool,  feathers,  etc.,  —  as  well  as  the  hoofs 
and  horns,  corresponding  to  the  nails  in  man,  are  modified  forms 
of  epidermal  tissue,  their  characteristic  ingredients  being  the 
class  of  albuminoids  designated  as  keratins  (51  e). 

92.  Composition.  —  Except  for  their  high  and  variable  sul- 
phur content,  the  keratins  differ  little  in  elementary  composi- 
tion from  the  simple  proteins,  but  they  are  much  more  resistant 
to  chemical  reagents,  being,  for  example,  insoluble  in  alkalies  in 
the  cold  and  unattacked  by  either  pepsin  or  trypsin.     These 
properties  fit  them  well  for  the  outer  covering  of  the  animal. 
The  following  table  shows  the  elementary  composition  of  some 
of  the  more  important  epidermal  tissues :  — 

TABLE  13.  —  COMPOSITION  OF  EPIDERMAL  TISSUES 


CARBON 
% 

HYDRO- 
GEN 
% 

NITRO- 
GEN 
% 

OXYGEN 

% 

SULPHUR 
% 

Epidermis  of  man  .... 
Hair  
Nails 

50.28 
50.65 

r  i  QO 

6.76 
6.36 

6  QA 

17.21 
17.14 
17  SI 

25.01 
20.85 

21  7S 

0.74 
5.00 
2  80 

Horn  of  cow  
Hoof  of  horse 

5I-03 
r  i  A.I 

6.80 

6  96 

16.24 
17  A6 

22.51 
IO  A.Q 

3-42 
422 

Pure  dry  wool  

4.0  6? 

7  26 

16  01 

23  6S 

•2.4.1 

Pure  dry  wool 

4.Q  80 

7  l6 

1608 

23.  IO 

3^7 

58  NUTRITION  OF   FARM  ANIMALS 


The  reserve  tissues 

93.  Food  storage.  —  The  classes  of  tissue  considered  in  the 
foregoing  paragraphs  may  be  said  in  a  general  way  to  constitute 
the  working  machinery  of  the  body.     They  are  composed  of 
cells  which  either  serve  the  organism  through  specific  activities 
of  their  protoplasm,  as  by  producing  motion  of  one  sort  or  an- 
other, transmitting  stimuli  or  secreting  enzyms  or  other  prod- 
ucts, or  which,  by  means  of   the   extraordinary  development 
of  their  intercellular  substance,  support  and  protect  the  various 
organs  of  the  body  as  a  whole. 

As  previously  stated,  however  (77),  many  cells  have  the 
power  of  storing  up  surplus  food  in  the  form  of  cell  enclosures, 
especially  as  fat  or  glycogen,  which  apparently  constitute 
no  part  of  the  protoplasm  itself  but  which  are  simply  re- 
serve material.  This  is  more  or  less  true  of  all  cells,  but 
certain  tissues  show  this  property  to  a  marked  degree  so  that 
they  may  properly  be  spoken  of  as  preeminently  the  reserve 
tissues. 

94.  Adipose   tissue.  —  The   most   familiar    and    most    im- 
portant form  of  reserve  tissue  is  adipose  tissue,  in  which  the 
stored  material  consists  of  fat  and  which  constitutes  the  great 
store  of  reserve  material  in  the  animal  body. 

Fat  in  the  form  of  minute  droplets  may  be  deposited  in  the 
cytoplasm  of  all  body  cells  but  the  presence  of  more  than  minute 

amounts  in  normal  cells  of  muscles, 
£-.-_•.  Nucleus,  nerves,  glands,  etc.,  is  unusual. 

It  is  particularly  in  certain  cells 
of  the  connective  tissue  that  the 
Fat  drop.  large  accumulations  of  visible  fat 

Cell-membrane.   jn  the  body  take  place.     At  the 
outset  these  cells  present  no  special 
/  ^faVd!;    characters,  but  in  a  well-nourished 

(Bohm,  Davidorf,  Huber,  Text  Book  ,     . 

of  Histology.)  animal  globules   of   fat    begin   to 

accumulate  in  them,  the  cells  en- 
large, the  globules  of  fat  coalesce  into  larger  ones  and  finally 
the  cell  substance  is  reduced  to  a  mere  envelope,  cytoplasm 
and  nucleus  being  pushed  to  one  side  and  almost  the  whole 
volume  of  the  cell  occupied  by  fat.  Masses  of  connective  tissue 
thus  loaded  with  fat  constitute  adipose  tissue. 


COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS     59 


FIG.  6 


The  increase  of  adipose  tissue,  according  to  Waters  and  Bell,1  takes 
place  in  two  ways  :  first  by  the  formation  of  new  cells  and  second  by 
an  increase  in  the  size  of  existing  cells  as  the  storage  of  fat  proceeds. 
They  observed  fat  cells 
ranging  from  20  //,  in  di- 
ameter in  an  emaciated 
animal  to  about  60  p  in  an 
animal  in  ordinary  thrifty 
condition  and  to  as  much 
as  200  /w.  in  a  very  fat 
animal.  The  corresponding 
relative  volumes,  therefore, 
are  1:27:  1000. 

There  are  two  regions  in 
particular  in  which  fat  tends 
to  accumulate,  viz.,  in  the 
subcutaneous  connective 
tissue  and  in  the  connective 
tissue  surrounding  the  in- 
ternal organs,  especially  that 
of  the  mesentery  and  omen- 
turn,  although  all  the  looser 
forms  of  connective  tissue, 
including,  as  already  noted, 
the  connective  tissue  lying 
between  and  within  the 
muscles,  may  serve  for  the 
storage  of  fat. 

95.  Composition  of 
adipose  tissue.  —  What  is 
here  called  adipose  tissue 
is  commonly  spoken  of  as 
fat,  but  it  is  evident  that 
only  a  portion  of  it  is  fat 
in  the  strict  sense,  the  re- 
mainder consisting  of  con- 
nective tissue,  made  up  of 
albuminoids,  or  collagens, 
together  with  their  ac- 

T     . 

companymg  water.     It  is 


FIG. 


FIGS.  6-8.  —  Successive  stages  in  the  forma- 

tion  of  adipose  tissue     (Hough  and  Sedgwick, 

this    nitrogenous    material    The  Human  Mechanism.) 

1  Proceedings,  Soc.  Prom.  Agri.  Science,  1909,  pp.  20-24. 


6o 


NUTRITION  OF  FARM  ANIMALS 


which  forms  the  "  cracklings  "  when  the  fat  is  melted  out  as  in 
making  lard  or  tallow. 

It  is  evident  that  the  composition  of  adipose  tissue  must 
vary  according  to  the  extent  to  which  the  deposition  of  fat  in  the 
cells  has  been  carried.  When  the  cells  are  enlarged  and  well 
filled  with  fat,  as  in  the  fattened  animal,  the  percentage  of  fat 
will  be  high  and  that  of  protein,  water  and  ash  correspondingly 
low.  When  there  has  been  little  deposition  of  fat,  or  when  fat 
previously  present  has  been  withdrawn  by  starvation,  the  fat 
content  will  be  low  and  the  percentage  of  protein,  water  and 
ash  will  be  high.  The  following  figures  reported  by  Beythien  for 
the  extremes  of  composition  of  the  adipose  tissue  of  commercial 
beef,  pork  and  mutton  serve  to  give  a  general  idea  of  the  com- 
position of  such  deposits  in  well-fed  animals. 

TABLE  14.  —  RANGE  OF  COMPOSITION  OF  ADIPOSE  TISSUE  OF  COMMERCIAL 

MEAT 


MINIMUM 

% 

MAXIMUM 

% 

Water 

^  04. 

18  73 

Fat    

76.10 

Q3  O2 

Nitrogenous  matter      
Ash 

1.84 
o  10 

4-97 
023 

As  an  illustration  of  the  variations  in  the  composition  of 
adipose  tissue  in  different  regions  of  the  body  the  following 
average  figures  found  by  Henneberg,  Kern  and  Wattenberg  for 
the  composition  of  the  fat  tissues  of  five  lambs  may  be  pre- 
sented. 

TABLE  15.  —  COMPOSITION  OF  ADIPOSE  TISSUE  OF  DIFFERENT  REGIONS 


* 

SUBCUTA- 
NEOUS FAT 

KIDNEY 
FAT 

INTESTINAL 
FAT 

Water 

II.OO 

4.36 

5.82 

Fat                         

84.40 

03.8o 

Q2.  IS 

Fat-free  dry  matter   

4.5i 

2.03 

IOO.OO 

IOO.OO 

IOO.OO 

COMPOSITION  OF  ANIMALS  AND   OF  FEEDING   STUFFS      6 1 

At  the  other  extreme  stand  the  figures  reported  by  Trow- 
bridge  l  for  the  composition  of  the  kidney  fat  of  a  steer  which 
had  received  a  submaintenance  ration  for  about  eleven  months 
and  was  in  a  very  reduced  condition :  — 

Water 81.42  per  cent 

Protein 9.60  per  cent 

Fat 4.59  per  cent 

96.  Glycogen  storage.  —  In  addition  to  the  large  accumula- 
tions of  fat  which  the  body  sometimes  contains,  a  much  more 
limited  storage  of  reserve  material  may  occur  in  the  form  of 
the  carbohydrate  glycogen,  especially  in  the  muscles  and  in  the 
liver. 

Neumeister  estimates  that  the  liver  of  the  average  man  may 
store  up  approximately  150  grams  of  glycogen  and  the  muscles 
and  other  tissues  approximately  the  same  amount,  making  a 
total  of  about  300  grams  for  the  entire  body.  Estimating  the 
weight  of  the  liver  of  a  1200  pound  steer  at  16  pounds  and  that 
of  the  muscles  at  800  pounds,  and  assuming  a  content  of  10  per 
cent  of  glycogen  in  the  liver  and  one  of  0.4  per  cent  in  the  mus- 
cles, the  total  amount  of  glycogen  contained  in  the  body  would 
be  approximately  2200  grams,  but  naturally  this  amount  would 
vary  greatly  at  different  times  according  to  the  conditions  of 
feeding  and  exercise. 

§  3.  THE  COMPOSITION  OF  THE  ANIMAL  AS  A  WHOLE 

97.  Composition  of  entire  body.  —  In  view  of  the  great  num- 
ber of  individual  chemical  compounds  already  discovered  in 
the  animal  body  and  of  the  lack  of  accurate  quantitative  methods 
for  the  determination  of  many  of  them,  any  complete  and  de- 
tailed estimate  of  the  composition  of  the  body  as  a  whole  is 
manifestly  impossible.     The  most  that  can  be  done  is  to  de- 
termine the  proportions  of  the  principal  groups  of  compounds 
enumerated  in  Chapter  I.     Several  such  investigations  have 
been  made  at  different  times.     In  all  of  them  water  and  dry 
matter,  as  well  as  the  fat  content  of  the  latter,  have  been  de- 
termined, while  sometimes  determinations  of  the  total  nitrogen 

1  Proc.  Amer.  Soc.  Animal  Nutrition,  1910,  p.  13. 


62 


NUTRITION  OF  FARM   ANIMALS 


or  of  the  ash  or  of  both  have  been  added.  From  such  investi- 
gations a  general  idea  may  be  reached  of  what  might  be  called 
the  gross  composition  of  the  body. 


TABLE  16.  —  COMPOSITION  OF  ENTIRE  BODIES  OF  ANIMALS  —  EMPTY 

WEIGHT 


SPE- 
CIES 

AGE 

CONDITION 

PERCENTAGE  COMPOSITION 

Ash 

Pro- 
tein 

Fat 

Dry 
Mat- 
ter 

Water 

{9-10  wks. 

Fat 

3-9 

iS-9 

iS-3 

34-9 

65.1 

Cattle 

4  yrs. 

Half-fat 

5-o 

18.4 

20.8 

43-9 

56.1 

4  yrs. 

Fat 

4.2 

15-4 

32.0 

51-6 

48.4 

6  mos. 

Fat 

3-2 

13-4 

31-2 

47-8 

52.2 

Lawes  and  Gilbert 

i  yr. 

Store 

3-4 

15-8 

19.9 

39-o 

61.0 

Phil.  Trans.,  Part  ' 

Sheep 

•       3i  yrs. 

Half-fat 

3-5 

iS-5 

2S--9 

44-8 

55-2 

II  (1859),  P-  493 

ii  yrs. 

Fat 

3-0 

13.0 

37-8 

53-8 

46.2 

if  yrs. 

Extra  fat 

3-i 

n.6 

48.3 

62.9 

37-1 

Swine 

f    ii-izmos. 

Store 

2.8 

14.6 

24.6 

41.9 

58.1 

\    n-i2mos. 

Fat 

t-7 

11.4 

43-9 

57-0 

43-0 

{16^  mos. 

— 

2.63 

12.71 

40.56 

56.11 

43-89 

Soxhlet 

Swine 

19  mos. 

— 

2-44 

12.92 

3S-69 

51.56 

48.44 

Centbl.  Agr.  Chem., 

19  mos. 

— 

2.17 

10.88 

44-59 

58-55 

41-45 

10  Ci88i),  674     . 

9  mos. 

Unfattened 

3-94  1 

22.76* 

19.03 

45-73 

54-27 

9  mos. 

Unfattened 

3-861 

23.  242 

15.80 

42.90 

57-10 

10  mos. 

Fattened 

3-211 

19.01  * 

24.49 

46.71 

53-29 

B.  Schulie 

10  mos. 

Fattened 

3-591 

17.822 

26.78 

48.19 

51-81 

Landw.   Jahrb.,   n 

^eese 

10  mos. 

Fattened 

3-381 

19.19* 

26.82 

49-39 

50.61 

(1882),  57        .     . 

10  mos. 

Fattened 

3-4i  l 

18.78* 

29.22 

5I-4I 

48.59 

10  mos. 

Fattened 

2.991 

I8.531 

25-36 

46.88 

53-12 

10  mos. 

Fattened 

3-i8i 

18.93  2 

26.21 

48-32 

51.68 

10  wks. 

Unfattened 

3-Si  3 

I4-304 

10.27 

28.08 

71-92 

Tschirwinsky 

• 

9  wks. 

Unfattened 

4-I43 

15.21  4 

10.39 

29.74 

70.26 

Landw.  Vers.  Stat., 

owine 

28  wks. 

Fattened 

2.623 

11.08* 

40.92 

54.62 

45.38 

29  (1883),  317      . 

23  wks. 

Fattened 

3-90  3 

11.70* 

27.77 

43-37 

56.63 

Chanicwski 

Mature 

Thin 

3-35 

26.93* 

6.65 

36.85 

63-15 

Ztschr.     Biol.,    20 

Mature 

Fat 

3-19 

23-90* 

12.68 

39.67 

60.33 

(1884),  179 

Geese 

Mature 

Fat 

2-79 

21.74* 

19.89 

44-36 

55.64 

(Computed  on  total 

Mature 

Fasted 

5-  n1 

2I-372 

3-26 

29.74 

70.26 

live  weight)     .     . 

Mature 

Fat 

3-941 

I9-981 

16.01 

39-93 

60.07 

Jordan 

23  mos. 

4-45 

17-381 

18.80 

40-63 

59-37 

Maine    Expt.    Sta., 

~*«ttlA 

23  mos. 

5-17 

17-51  * 

20.19 

42.87 

57-13 

Kept.  1895,  II,  36 

^aine 

33  mos. 

S-I4 

16.59! 

25.18 

46.91 

53-09 

(Hides  not  included) 

33  mos. 

5-24 

16.73  ' 

24.62 

46.59 

53-41 

o 

6.151 

12.19 

i-3i 

19-65 

80.35 

0 

6.361 

11.92 

i-55 

19-83 

80.17 

Wilson 

. 

0 

6.361 

12.51 

i.  60 

20.46 

79-54 

Amer.  Jour.  Physiol., 

jwine 

1  6  days 

3-92  l 

14-57 

1.29 

19.78 

80.22 

8  (1903),  197 

1  6  days 

4-15  ' 

14.78 

1-43 

20.36 

79.64 

1  6  days 

4.561 

14-13 

i-35 

20.04 

79-96 

1  By  difference. 

p  By  difference  in  soft  parts. 


2  Includes  feathers. 

4  By  difference  in  bones. 


COMPOSITION  OF  ANIMALS  AND  OF   FEEDING  STUFFS      63 


The  earliest  investigation  of  this  sort  was  that  of  Lawes  and 
Gilbert 1  in  1859,  already  several  times  referred  to,  in  which 
analyses  were  made  of  both  the  carcass  and  the  offal  parts  of 
ten  animals,  viz.,  a  fat  calf,  a  half -fat  ox,  a  moderately  fat  ox, 
a  fat  lamb,  a  store  sheep,  a  half-fat  sheep,  a  fat  sheep,  a  very 
fat  sheep,  a  store  pig  and  a  fat  pig.  The  determinations  made 
included  total  dry  matter,  ash,  fat  and  total  nitrogen.  Several 
later  investigators  have  also  reported  analyses  of  the  entire 
bodies  of  animals,  including  cattle,  swine  and  geese. 

Table  16  contains  the  results  of  these  various  investigations 
up  to  1903  arranged  chronologically.  In  all  cases  where  the 
data  given  permit,  the  results  have  been  computed  upon  the 
"  empty  "  weight  of  the  animals,  that  is,  upon  the  live  weight 
minus  the  contents  of  the  digestive  tract.  On  account  of 
this  recalculation,  the  figures  for  Lawes  and  Gilbert's  results 
differ  somewhat  from  those  usually  cited.  In  all  cases  where 
nitrogen  was  determined  the  "  protein  "  equals  N  X  6.25.  In 
those  cases  in  which  nitrogen  was  not  determined  the  protein 
is  equivalent  to  fat-  and  ash-free  dry  matter. 

Haecker,2  as  the  result  of  analyses  of  the  bodies  of  sixty  well- 
fed  steers,  has  reported  the  following  average  composition  at 
various  weights. 

TABLE  17. —  COMPOSITION  OF  STEERS  AT  VARIOUS  STAGES —  EMPTY 

WEIGHT 


NORMAL  WEIGHT 

LBS. 

WATER 

.      % 

DRY  MATTER 
% 

PROTEIN 

% 

FAT 

% 

ASH 

% 

100 

71-85 

28.15 

19.90 

3-99 

4.26 

200 

69.47 

30-53 

19.63 

6.26 

4.64 

300 

66.31 

33-69 

19-35 

9.84 

4-50 

400 

65.76 

34-24 

19-31 

10.56 

4-37 

500 

62.91 

37-09 

19.15 

13-73 

4.21 

600 

62.21 

37-79 

19.22 

13.97 

4.60 

700 

60.75 

39-25 

18.83 

15.91 

4-51 

800 

57.88 

42.12 

18.69 

19-23 

4.20 

900 

54-09 

45-90 

17.66 

24.08 

4.16 

IOOO 

53-09 

46.91 

17-57 

25-53 

3-8i 

IIOO 

48.02 

51.98 

16.19 

3L9I 

3-88 

I2OO 

48.64 

5!-36 

15.66 

31.10 

3.67 

J  Phil.  Trans.,  Part  II,  1859,  p.  493. 

2  Amer.  Soc.  Animal  Produc.,  Proc.,  1914,  p.  18. 


64  NUTRITION  OF  FARM   ANIMALS 

It  appears  from  the  foregoing  figures  that  the  most  abundant 
single  constituent,  although  one  which  is  subject  to  marked 
variations,  is  water,  its  percentage  ranging  from  over  80  in 
very  young  pigs  to  37  in  a  very  fat  sheep.  Only  in  this  latter 
case  and  two  others  does  the  percentage  of  water  fall  below 
that  of  fat.  Relatively,  the  greatest  variations  are  in  the  fat, 
as  would  be  expected,  since  fat  is  the  reserve  material  of  the 


TABLE  18.  —  COMPOSITION  OF  FAT-FREE  BODY  —  EMPTY  WEIGHT 


LIVE 
WEIGHT 
LBS. 

AGE 

ASH 

PRO- 
TEIN 

DRY 
MATTER 

WATER 

Cattle 

Lawes  and  Gilbert  . 

— 

9-10  wks. 

4.60 

18.80 

23.10 

76.90 

Jordan 



23—33  rnos. 

6.45 

21  Q2 

28  ^7 

7  1-63 

Lawes  and  Gilbert  . 

— 

4yrs. 

6.30 

*  A  »v 

23.20 

29.00 

71.00 

f 

1-1   A       Q  1 

IOO 

4-44 

20.73 

25-I7 

74-°3 

/i  r*    Qr\ 

2OO 

4-95 

20.94 

25.09 

74.11 

300 



4.99 

21.46 

26.45 

73-55 

.  o.~ 

r>f\     A  R 

400 

4.09 

21.59 

2O.4O 

73-52 

500 



4.88 

22.20 

27.08 

72.92 

Haecker     .... 

,    600 



5-35 

22-34 

27.69 

72.31 

e   if\ 

700 

.5-3° 

22.39 

27.70 

72.24 

800 



5-20 

23.14 

28.34 

71.66 

o 

r 

Oo  -  . 

/• 

900 

5-4 

23.70 

25.74 

71.20 

IOOO 
I  IOO 



5.12 

5-70 

23-59 
23.78 

28.71 
29.48 

71.29 
70.52 

, 

OA  n& 

.           . 

V»    1  2OO 

5-33 

24.00 

29.41 

7°-59 

Sheep 

Lawes  and  Gilbert  . 

— 

6  mos. 

4.60 

19.60 

24.IO 

75-90 

Lawes  and  Gilbert  . 

— 

1-2  yrs. 

5-oo 

21.  2O 

25.90 

74.10 

Lawes  and  Gilbert  . 

— 

3l  y^. 

4.70 

21.10 

25-50 

74-50 

Swine 

Wilson       .... 

— 

New  born 

6.38 

12.39 

18.77 

81.23 

Wilson       .... 

— 

1  6  days 

4.27 

14.69 

18.96 

81.04 

Tschirwinsky       .     . 

— 

9-10  wks. 

4.27 

16.45 

2O.72 

79.28 

Tschirwinsky       .     . 

— 

23-28  wks. 

4.92 

17-47 

22.39 

77.61 

Lawes  and  Gilbert 

— 

11-12  mos. 

3-40 

19.90 

23.10 

76.90 

Soxhlet       .... 

— 

17-19  mos. 

4-04 

20.37 

25-34 

74-66 

Geese 

B.  Schulze      .     .     . 

— 

9-10  mos. 

4-54 

26.06 

30.60 

69.40 

Chaniewski     .     .     . 

— 

Mature 

4.14 

25.85 

29-93 

70.07 

COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS     65 

body  and  may  be  stored  up  in  large  quantities,  reaching  in  one 
instance  48  per  cent,  or,  on  the  other  hand,  may  be  almost  lack- 
ing in  the  insufficiently  fed  or  fasted  animal. 

98.  Composition  of  fat-free  body.  —  Since  the  adipose  tissue 
of  the  animal  body  represents  substantially  a  storage  of  reserve 
material  (93,  94)  temporarily  set  aside  from  the  physiological 
activities  of  the   organism,  a  better  idea  of  the  composition 
of  the  working  machinery  of  the  body  is  obtained  by  computing 
its  composition  fat-free  as  in  Table  18. 

When  this  is  done,  it  appears  that  the  composition  of  the  fat- 
free  body  is  much  less  variable  than  that  of  the  body  as  a  whole, 
the  chief  difference  being  due  to  variations  in  the  water  content, 
which  in  turn  depends  chiefly  upon  the  age  of  the  animal,  as 
the  preceding  table  shows.  So  far  as  can  be  concluded  from 
these  few  cases,  however,  the  fat-free  bodies  of  mature  cattle 
would  appear  to  contain  three  to  four  per  cent  less  water  than 
those  of  mature  sheep  or  swine.  In  the  case  of  geese,  the  per- 
centage of  water  is  probably  low  on  account  of  the  relatively 
small  amount  in  the  feathers. 

99.  Composition  of  fat-  and  ash-free  dry  matter.  —  In  some  of 
the  foregoing  investigations,  viz.,  in  Lawes  and  Gilbert's,  Sox- 
hlet's  and  three  of  Chaniewski's,  the  total  nitrogen  was  deter- 
mined and  the  protein  has  been  calculated  by  multiplying  by 
the  factor  6.25.     These  experiments  permit  a  computation  of 
the  percentage  of  nitrogen  contained  in  the  fat-free  dry  matter 
which  in  the  other  experiments  has  been  regarded  as  protein. 
For  example,  in  the  case  of  Lawes  and  Gilbert's  fat  calf  the  figures 
are  as  follows :  — 

Per  cent 

Total  dry  matter 34.9 

Ash 3.9 

Fat        15.3     19.2 

Fat-  and  ash-free  dry  matter     .     .     .     15.7 
Total  nitrogen 2.537 

2-537  •*•  J5-7  =  16.16%  nitrogen  in  ash-  and  fat-free  dry 
matter. 

The  results  of  such  a  computation  for  all  of  the  experiments 
in  which  the  published  data  permit  it  are  contained  in 
Table  19. 


66  NUTRITION  OF   FARM   ANIMALS 

TABLE  19.  —  NITROGEN  IN  FAT-  AND  ASH-FREE  DRY  MATTER 


EMPTY 

WEIGHT 

NITROGEN 
IN  FAT-  AND 

Fat-  and 
Ash-free  Dry 
Matter 

% 

Nitrogen 

% 

ASH-FREE 
DRY 
MATTER 

% 

Fat  calf 

IS-7 

2-537 

16.16 

Half-fat  ox 

18.1 

2.950 

16.30 

Fat  ox 

15-4 

2.466 

16.01 

Fat  lamb 

13-4 

2.150 

16.05 

Store  sheep 

15-7 

2-525 

16.08 

Lawes  and  Gilbert  .     . 

Half-fat  sheep 

15-4 

2.486 

16.14 

Fat  sheep 

13.0 

2.085 

16.04 

Extra-fat  sheep 

ii.  5 

1-857 

16.15 

Store  pig 

14-5 

2.342 

16.15 

Fat  pig 

11.4 

1.830 

16.05 

Average 

i6.n 

Swine 

15-54 

2.033 

13.08 

Soxhlet 

Swine 

15-87 

2.068 

13-03 

Swine 

14.00 

1.741 

12.44 

Average 

12.85 

Geese 

26.84 

4-309 

16.06 

Chaniewski     .... 

Geese 
Geese 

23.80 
21.68 

3.824 
3-479 

16.07 
16.05 

Average 

16.06 

With  the  exception  of  Soxhlet's  experiments,  the  percentage 
of  nitrogen  approximates  closely  to  that  of  animal  proteins. 
If  account  be  taken  of  the  fact  that  the  ether-extraction  method 
used  in  these  investigations  does  not  completely  remove  the 
fat  from  dried  animal  tissue,  the  conclusion  appears  justified  that 
the  organic  matter  other  than  fat  contained  in  the  animal  body 
has  substantially  the  composition  of  protein. 

§  4.   THE  COMPOSITION  or  FEEDING  STUFFS 

100.  Groups  of  ingredients.  —  As  in  the  case  of  the  animal 
body,  the  vast  number  of  single  chemical  compounds  found 
in  the  plant,  as  well  as  the  lack  of  accurate  quantitative  methods 
for  the  determination  of  many  of  them,  renders  it  practically 


COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS    67 

necessary  to  be  content  in  most  cases  with  a  separation  of  the 
plant  substances  into  a  few  major  groups  or  sub-groups  of  in- 
gredients. As  ordinarily  carried  out,  feeding  stuffs  analysis 
recognizes  seven  of  these  categories,  viz.,  water,  ash,  protein, 
non-protein,  ether  extract,  crude  fiber  and  nitrogen-free  ex- 
tract. 

101.  Water.  —  The  amount  of  water  in  a  feeding  stuff  is 
commonly  inferred  from  the  loss  of  weight  which  the  substance 
undergoes  at  a  temperature  above  the  boiling  point  of  water. 
There  is  also  a  possibility,  however,  of  a  loss  of  other  volatile 
matter  besides  water,  while,  on  the  other  hand,  some  substances 
tend  to  absorb  oxygen  and  thus  increase  in  weight,  especially 
when  dried  in  air  at  a  high  temperature.     The  exact  deter- 
mination of  water  and  dry  matter,  therefore,  is  by  no  means  an 
easy  problem,  but  the  results  obtained  by  the  ordinary  methods 
are  sufficiently  exact  for  almost  all  purposes  related  to  stock 
feeding.     Commonly,  the  residue  is  weighed  and  regarded  as 
dry  matter,  the  amount  of  water  being  obtained  by  difference. 

102.  Ash.  —  In  the  ordinary  feeding  stuffs  analysis,  ash  is 
equivalent  to  the  residue  left  after  complete  incineration  of  the 
substance  in  air  or  oxygen,  the  process  being  carried  out  at  as 
low  a  temperature  as  practicable  in  order  to  avoid  volatilization 
of  part  of  the  alkalies  present. 

That  this  method  fails  entirely  to  distinguish  between  those  ele- 
ments which  were  originally  present  as  electrolytes  and  those  which 
were  in  organic  combination  has  already  been  pointed  out  (5) ,  as  has 
also  the  fact  that  certain  elements,  notably  sulphur  and  phosphorus, 
are  only  partially  recovered  in  the  ash  by  the  ordinary  method  of 
preparation.  As  the  study  of  the  functions  of  the  ash  ingredients  pro- 
gresses, it  may  be  anticipated  that  we  shall  come  to  determine  the 
several  elements  involved  in  the  way  most  appropriate  to  each  rather 
than  simply  to  determine  the  ash  as  a  whole. 

103.  Nitrogenous  constituents.  —  As  yet  no  methods  exist 
for  the  quantitative  separation  of  the  nitrogenous  constituents 
from  the  other  ingredients  of  plants.     While  much  labor  has 
been  expended  upon  a  study  of  the  individual  proteins  of  a  com- 
paratively few  vegetable  materials,  and  while  in  some  instances 
it  is  possible  to  state  with  approximate  accuracy  the  amounts 
of  the  several  proteins  present,  nevertheless  the  only  available 
methods  for  the  determination  of  the  nitrogenous  compounds 


68  NUTRITION  OF  FARM  ANIMALS 

of  feeding  stuffs  in  general  are  indirect  ones  based  upon  a 
determination  of  their  characteristic  element  nitrogen. 

104.  Crude  protein.  —  In  the  method  of  feeding  stuffs  anal- 
ysis inherited  from  the  early  investigations  of  Henneberg  and 
Stohmann,  the  protein  is  estimated  from  the  amount  of  total 
nitrogen  upon  two  assumptions:    first,  that  all  the  proteins 
contain  16  per  cent  of  nitrogen  and,  second,  that  all  the  nitro- 
gen of  feeding  stuffs  exists  in  the  protein  form.     On  the  basis 
of  these  assumptions,  the  protein  is,  of  course,  equal  to  total 
nitrogen  multiplied  by  6.25.     The  protein  as  thus  determined 
is  designated  as  crude  protein  to  indicate  the  approximate  na- 
ture of  the  determination. 

Subsequent  investigations  by  Scheibler,  E.  Schulze,  Kellner 
and  others  have  shown  the  presence  in  many  feeding  stuffs 
of  relatively  large  amounts  of  non-protein  nitrogenous  com- 
pounds, so  that  it  is  desirable  to  distinguish  at  least  between  the 
nitrogen  present  as  true  protein  and  that  present  in  the  simpler 
compounds  grouped  under  the  general  term  non-protein 
(60-67) ,  and  all  analyses  of  feeding  stuffs  for  scientific  purposes 
should  at  least  make  this  distinction.  Logically,  too,  the  term 
crude  protein  should  be  dropped  altogether,  but  when,  as  in 
the  case  of  the  older  analyses,  this  is  impracticable,  care  should 
be  taken  to  retain  the  adjective,  reserving  the  term  "  protein  " 
for  use  in  the  sense  given  it  in  the  next  paragraph. 

105.  True  protein.  —  As  a  means  of  effecting  an  approximate 
separation   of   the   true  protein   from   the   other   nitrogenous 
compounds  present  in  plants,  advantage  is  taken  of  the  fact 
that  most  of  the  latter  class  of  substances  are  soluble  in  water. 
An   aqueous   extract   of   a    feeding   stuff,   therefore,  contains 
by  far  the  larger  share  of  its  non-protein.     Such  an  extract, 
however,  contains    also    any  water-soluble    proteins    existing 
in  the  substance.     These  are  removed  in  part  by  coagulation  by 
heating,  i.e.,  by  boiling  the  solution,  and  in  part  by  the  addition 
of  some  reagent  with  which  they  form  insoluble  compounds. 
Various  substances  have  been  used  for  this  purpose  but  the 
present  official  method  of  analysis,  based  upon  Stutzer's  inves- 
tigations, uses  copper  hydrate  as  the  precipitant.     In  practice, 
the  feeding  stuff  is  boiled  with  water,  the  precipitant  added 
and  the  soluble  matter  filtered  off.     The  nitrogen  of  the  in- 
soluble residue  is  regarded  as  being  protein  nitrogen  and  from 


COMPOSITION  OF  ANIMALS  AND   OF  FEEDING  STUFFS      69 

it  by  multiplication  by  6.25  (or  some  other  agreed  factor)  the 
amount  of  protein  is  calculated. 

It  is  obvious  that  this  method  of  determining  protein  is  sub- 
stantially a  conventional  method  and  that  the  adjective  true 
is  employed  in  a  somewhat  Pickwickian  sense.  The  result 
probably  includes  all  of  the  proteins  of  the  feed  but  may  also 
include  other  insoluble  nitrogenous  compounds. 

106.  Non-protein.  —  The  non-protein  in  feeding  stuffs  analy- 
sis includes  all  the  nitrogenous  compounds  which  remain  in 
solution  when  the  material  is  treated  in  the  manner  just  de- 
scribed for  the  determination  of  protein.     The  nitrogen  may 
be  determined  in  the  solution  but  ordinarily  it  is  obtained  by 
subtracting  the  protein  nitrogen  from  the  total  nitrogen.     The 
difference,  multiplied  by  some  conventional  factor,  equals  the 
non-protein.     Obviously,  the  non-protein  is   a   heterogeneous 
mixture,  varying  as  between  different  feeding  stuffs  and  even 
in  the  same  feeding  stuff  grown  or  harvested  under  different 
conditions. 

107.  Nitrogen  factors.  —  Evidently  the  accuracy  with  which 
the  protein  and  the  non-protein  in  a  feeding  stuff  are  determined 
depends  not  only  upon  the  accuracy  with  which  the  protein 
and  non-protein  nitrogen  can  be  separated  and  determined  but 
also  on  the  correctness  of  the  factors  used  for  converting  nitro- 
gen into  protein  or  non-protein  respectively. 

For  protein  the  usual  factor  has  been  6.25  as  already  stated, 
based  upon  the  assumption  of  16  per  cent  of  nitrogen  in  average 
protein.  As  was  stated  in  Chapter  I  (44),  however,  different 
proteins  vary  in  their  nitrogen  content,  and  in  particular  the 
vegetable  proteins  run  higher  in  nitrogen  than  the  animal  pro- 
teins, which  is,  of  course,  equivalent  to  a  smaller  conversion 
factor.  But  while  it  is  easily  shown  that  the  present  factor  is 
incorrect  in  many  cases,  it  is  not  so  easy  to  find  a  substitute. 
There  is  a  rather  wide  range  in  the  nitrogen  content  of  the 
individual  vegetable  proteins,  while  most  feeding  stuffs  con- 
tain two  or  more  proteins  in  unknown  proportions.  Moreover, 
the  proteins  of  the  majority  of  feeding  stuffs,  especially  of  the 
roughages,  have  not  yet  been  separated  and  studied. 

Ritthausen  1  has  suggested  the  use  of  the  factor  5.7  for  the 
majority  of  cereal  grains  and  leguminous  seeds,  5.5  for  the  oil 
1  Landw.  Vers.  Stat.,  47  (1896),  391. 


70  NUTRITION  OF   FARM   ANIMALS 

seeds  and  for  lupines,  and  6.0  for  barley,  maize,  buckwheat, 
soybean,  white  bean,  and  rape  and  other  brassicas. 

For  various  classes  of  human  foods,  Atwater  and  Bryant l  have 
proposed  the  following  factors  for  the  computation  of  protein 
from  protein  nitrogen  :  — 

Animal  foods 6.25 

Wheat,  rye,  barley  and  their  manufactured  products  .     .     .     .  5.70 
Maize,   oats,  buckwheat   and  rice,   and   their  manufactured 

products 6.00 

Dried  seeds  of  legumes        6.25 

Vegetables • 5.65 

Fruits 5.80 

For  feeding  stuffs  whose  proteins  have  not  yet  been  studied, 
there  seems  to  be  no  reason  for  changing  from  the  present 
usage. 

With  the  non-proteins  the  case  is  even  more  perplexing  in 
view  of  the  greater  variety  of  substances  included  under  this 
term  and  the  wide  range  of  their  nitrogen  content.  The 
writer  has  used  tentatively  4.7,  the  factor  for  asparagin  (66), 
one  of  the  most  widely  distributed  substances  of  this  class,  but 
the  choice  of  this  factor  is  substantially  arbitrary. 

108.  Crude  fat.  Ether  extract.  —  The  methods  for  de- 
termining the  fat  content  of  feeds  are  based  upon  its  extrac- 
tion by  means  of  some  solvent  which  dissolves  as  little  as 
possible  of  the  other  ingredients.  A  variety  of  solvents  has 
been  used  for  this  purpose,  such  as  carbon  disulphid,  carbon 
tetrachlorid,  petroleum  ether  and  the  like,  but  the  one  most 
commonly  employed  is  ethyl  ether,  or  the  so-called  "  sulphuric  " 
ether  commonly  used  as  an  anaesthetic. 

All  the  various  solvents  used,  however,  remove  other  sub- 
stances besides  neutral  fats  and  fatty  acids,  including  more  or 
less  of  the  more  complex  lipoids.  In  particular  the  ether  ex- 
tract obtained  from  coarse  fodders  contains  a  variety  of  waxes, 
resins,  etc.,  as  well  as  the  chlorophyl  of  the  leaves,  and  a  rela- 
tively small  proportion  of  true  fats.  It  is  customary,  there- 
fore, to  designate  the  extracted  material  as  "  crude  fat "  or, 
since  ether  is  the  reagent  ordinarily  used,  as  "  ether  extract." 

1  Storrs  (Conn.)  Agr.  Expt.  Sta.,  Rpt.,  12,  79. 


COMPOSITION  OF  ANIMALS  AND   OF   FEEDING   STUFFS      71 

If  a  different  solvent  is  used,  this  should  be  specified  in  the  state- 
ment of  the  analysis. 

109.  Crude  fiber.  —  The  so-called  crude  fiber  of  feeding  stuffs 
is  determined  by  boiling  them  first  with  dilute  acid  and  then 
with  dilute  alkali  under  strictly  defined  conditions  of  concen- 
tration and  time,  and  washing  the  undissolved  residue  with 
alcohol  and  ether.  The  residue,  after  deducting  the  small 
amount  of  ash  remaining  in  it,  constitutes  the  crude  fiber. 

Crude  fiber  as  thus  obtained  contains  most  of  the  cellulose, 
lignin  and  cutin  of  the  feeding  stuff,  along  with  more  or  less 
of  the  more  difficultly  soluble  hemicelluloses,  particularly  those 
containing  pentosans.  The  proportion  of  pentosans  contained 
in  the  crude  fiber  naturally  varies  according  to  the  nature  of 
the  feeding  stuff.  Tollens, l  for  example,  obtained  the  fol- 
lowing figures  for  the  crude  fiber  of  meadow  hay  and  of  brewers' 
grains :  — 


PENTOSANS  IN 
CRUDE  FIBER 

PER  CENT  OF  TOTAL 
PENTOSANS  OF  FEED 
RETAINED  m  CRUDE 
FIBER 

Meadow  hay 

16  89 

2^63 

Brewers'  grains 

1  1  61 

8  56 

110.  Nitrogen-free  extract.  —  All  the  ingredients  of  feeding 
stuffs  which  are  not  included  in  the  foregoing  six  categories, 
viz.,  water,  ash,  protein,  non-protein,  ether  extract  and  crude 
fiber,  are  usually  grouped  together  under  the  collective  name  of 
nitrogen-free  extract.  The  significance  of  the  name  is  evident. 
By  definition  the  nitrogen-free  extract  includes  all  those  non- 
nitrogenous  organic  constituents,  other  than  fat,  which  are 
extracted  from  the  feeding  stuff  in  the  process  of  determining 
the  crude  fiber.  The  amount  of  nitrogen-free  extract  in  a 
feeding  stuff  is  not  ascertained  by  any  process  of  direct  deter- 
mination but  simply  by  subtracting  the  sum  of  the  other  six 
groups  from  100  per  cent.  Such  a  residual  group  naturally  in- 
cludes a  great  variety  of  substances  of  very  diverse  nature, 2 

1  Jour.  Landw.,  45  (1897),  103. 

2  For  an  enumeration  of  the  principal  ingredients  of  the  nitrogen-free  extract, 
compare  Tollens,  Jour.  Landw.,  45  (1897),  295. 


72  NUTRITION  OF  FARM   ANIMALS 

but  as  a  rule  the  nitrogen-free  extract  consists  to  a  considerable 
extent  of  carbohydrates  of  one  sort  or  another.  Indeed,  it  has 
sometimes  been  designated  by  the  latter  name,  but  the  use  of 
the  word  in  this  sense  is  misleading  and  undesirable. 

The  nitrogen-free  extract  includes  not  only  hexose  but  also 
pentose  carbohydrates,  these  latter  substances  being,  therefore, 
by  the  ordinary  method  of  feeding  stuffs  analysis,  divided  be- 
tween the  crude  fiber  and  nitrogen-free  extract.  Some  of 
these  various  carbohydrates  can  be  determined  separately  with 
a  reasonable  degree  of  accuracy,  while  others,  including  unfor- 
tunately starch,  can  be  determined  only  more  or  less  approxi- 
mately. That  the  nitrogen-free  extract  is  far  from  consisting 
exclusively  of  carbohydrates  has  been  strikingly  shown,  by 
Stone.1  He  determined  the  content  of  the  various  classes  of 
carbohydrates  in  samples  of  wheat  and  maize  as  accurately  as 
possible  and  found  that  the  sum  in  both  cases  was  considerably 
less  than  the  amount  of  nitrogen-free  extract  as  determined 
by  the  conventional  method.  Much  greater  differences  in  this 
respect  have  been  shown  to  exist  in  roughages. 

111.  Classes  of  feeding  stuffs.  — •  The  composition  and  char- 
acteristics of  the  principal  classes  of  feeding  stuffs  are  considered 
in  Chapter  XV,  but  it  seems  desirable  to  anticipate  that  dis- 
cussion here  to  the  extent  of  indicating  the  three  major  classes 
into  which  the  feeding  stuffs  are  commonly  divided.  This 
classification  is  based  primarily  on  botanical  characteristics 
with  which,  however,  are  associated  corresponding  differences 
in  chemical  composition. 

Concentrates  or  concentrated  feeds.  —  As  the  name  implies, 
these  are  feeding  stuffs  which  contain  much  nutriment  in  a 
small  bulk.  They  include  primarily  the  grains  and  other  seeds 
and,  secondarily,  a  wide  range  of  technical  by-products  de- 
rived from  them  as  well  as  certain  by-products  of  animal  origin. 
Chemically,  they  are  characterized  by  their  relatively  low  con- 
tent of  crude  fiber,  ranging  from  practically  zero  in  certain  by- 
products to  perhaps  10  or  12  per  cent  in  grains  having  a  con- 
siderable proportion  of  hulls,  like  oats  or  buckwheat,  and  in 
certain  by-products. 

Coarse  fodders  or  roughage.  — •  Botanically,  these  consist  of 
the  vegetative  organs  of  the  plant,  i.  e.,  substantially  of  stalks 

1  Jour.  Amer.  Chem.  Soc.,  19  (1897),  183. 


COMPOSITION  OF  ANIMALS  AND  OF  FEEDING  STUFFS      73 

and  leaves.  They  include  hay,  straw  and  other  forms  of  for- 
age either  fresh,  ensiled  or  dried.  Chemically,  they  are  char- 
acterized by  their  relatively  high  percentage  of  crude  fiber, 
which,  however,  naturally  varies  within  quite  wide  limits. 
As  compared  with  the  concentrates  they  are  bulky  feeds  and 
contain  a  larger  proportion  of  difficultly  soluble  ingredients. 

Roots  and  tubers.  —  These  feeding  stuffs  contain  a  large  per- 
centage of  water,  resembling  in  this  respect  the  fresh  or  ensiled 
roughages.  Their  dry  matter,  on  the  other  hand,  resembles 
that  of  the  concentrates  in  containing  relatively  little  crude 
fiber  and  a  large  proportion  of  ingredients  which  are  easily 
soluble.  They  might  be  briefly  characterized  as  dilute  con- 
centrates. 


PART    II 
THE    PROCESSES    OF    NUTRITION 


CHAPTER   III 

DIGESTION  AND   RESORPTION 

112.  The  first  step  in  nutrition.  —  The  facts  considered  in 
Part  I  have  served  incidentally  to  show  some  particulars  of 
those  differences  between  the  feed  of  herbivora  and  the  animal 
body  which  it  serves  to  nourish  which  are,  in  a  general  way, 
familiar  to  every  one.     The  former  contains  many  ingredients 
not  found  in  the  latter,  and  it  is  plain  that,  for  example,  sub- 
stances like  starch  and  cellulose  must  undergo  considerable 
modification  before  they  can  be  used  in  the  animal  organism. 
One  need  not  be  a  chemist,  however,  to  reach  this  conclusion. 
A  simple  comparison  of  the  feeds  given  farm  animals  with  the 
products  which  they  manufacture  out  of  them  convinces  one 
that  profound  changes  are  necessary  to  convert  hay  and  grain 
into  meat  or  milk.     The  first  step  in  this  process  is  the  diges- 
tion of  the  feed.     In  all  but  the  lowest  animals,  special  tissues 
are  set  apart  for  this  work,  together  constituting  the  organs 
of  digestion,  or  the  alimentary  canal  with  its  appendages. 

§  i.  THE  ORGANS  OF  DIGESTION 

113.  General  plan.  —  The  process  of  digestion  is  seen  in  its 
simplest  form  in  unicellular  animals  like  the  ameba.     When 
the  ameba  comes  in  contact  with  a  particle  of  feed,  a  depres- 
sion forms  in  its  outer  surface  which  finally  closes  around  the 
particle,  forming  a  cavity  which  serves  as  a  temporary  digestive 
organ.     Undigested  residues  are  rejected  by  the  reverse  pro- 
cess.    In  animals  slightly  higher  in  the  scale,  this  temporary 
cavity  becomes  a  permanent  one,  the  same  opening  serving  for 
the  entrance  of  feed  and  the  exit  of  waste.     The  next  step  in 
the  evolution  is  the  provision  of  a  separate  exit  for  the  waste 
matter,  thus  giving  the  typical  form  of  digestive  apparatus, 
of  which  that  of  the  higher  animals  is  a  development,  consisting 

77 


7  8  NUTRITION  OF   FARM  ANIMALS 

of  a  cavity  or  cavities  communicating  with  the  external  world 
by  two  openings,  one  for  the  reception  of  feed  and  the  other 
for  the  rejection  of  waste.  In  domestic  animals,  the  digestive 
tract  is  large  and  of  very  complex  structure,  but  in  all  cases  it 
is  built  upon  the  general  plan  just  outlined.  -Always,  from  the 
ameba  up  to  man,  the  inner  surface  of  the  digestive  cavity  is 
morphologically  simply  a  continuation  of  the  external  surface 
of  the  body,  turned  in  as  one  might  a  glove  finger.  Conse- 
quently, the  material  contained  in  the  digestive  cavity,  strictly 
speaking,  is  still  outside  the  body.1 

Finally,  as  an  essential  part  of  the  digestive  apparatus,  there 
must  be  such  organs  as  the  cilia,  tentacles,  proboscis,  lips,  etc., 
by  which  feed  is  grasped  and  introduced  into  the  digestive  cavity, 
and  likewise  means  by  which  it  may  be  mechanically  ground 
to  fit  it  for  the  process  of  digestion,  as,  for  example,  the  teeth 
of  mammals,  the  bills  and  gizzards  of  birds,  etc. 

For  the  present  purpose,  it  is  unnecessary  to  enter  into  any 
elaborate  consideration  of  the  anatomy  of  the  digestive  organs, 
since  we  are  concerned  chiefly  with  the  chemical  rather  than 
the  physical  processes  of  digestion,  and  this  section  may  be 
confined  to  a  very  general  description  of  the  digestive  organs 
of  domestic  animals.  In  these  animals,  the  digestive  apparatus 
may  be  described  briefly  as  a  tube  having  various  enlargements, 
folds  and  diverticula. 

114.  Digestive  fluids  and  enzyms.  —  In  the  ameba,  what- 
ever changes  are  effected  in  the  substances  which  it  takes  as 
feed  are  accomplished  by  the  cells  of  the  introverted  surface 
or  by  their  secretions.  As  the  digestive  apparatus  becomes 
more  complicated,  however,  a  division  of  cellular  labor  takes 
place  and  certain  groups  of  cells  are  set  apart  to  produce  the 
digestive  juices  which  act  upon  the  feed.  In  the  higher  animals, 
these  cells  become  the  numerous  secreting  glands  which  are 
an  essential  part  of  the  organs  of  digestion.  The  principal 
active  agents  in  digestion  are  certain  enzyms  secreted  by  these 
glands,  the  more  important  digestive  enzyms  in  the  higher 
animals  being :  — • 

i.  The  amylases,  ptyalin  (in 'the  saliva)  and  amylopsin  (in 
the  pancreatic  juice),  acting  upon  starch. 

1  For  a  more  complete  discussion  of  the  development  of  the  digestive  apparatus 
see  R.  Meade  Smith,  The  Physiology  of  the  Domestic  Animals,  pp.  203-226. 


DIGESTION  AND   RESORPTION  79 

2.  The  invertases,  sucrase,  maltase  and  lactase  (in  the  in- 
testinal juice),  acting  upon  di-saccharids. 

3.  The  proteases,  pepsin   (in   the  gastric  juice),  trypsin  (in 
the  pancreatic  juice)  and  erepsin  (in  the  intestinal  juice),  act- 
ing upon  proteins. 

4.  The  lipase,  steapsin  (in  the  pancreatic  juice),  acting  upon 
the  lipoids,  or  specifically  the  fats. 

115.  The  mouth.  —  The  mouth  is  the  organ  of  prehension 
and  mastication.     Chiefly  by  means  of  the  tongue,  lips  and 
teeth,  feed  is  seized  and  introduced  into  the  digestive  cavity, 
while  the  teeth  serve  also  to  grind  it  up,  rendering  it  capable 
of  being  swallowed  and  also  exposing  more  surface  to  the  action 
of  the  digestive  fluids.     The  mouth  also  receives  the  secretion 
of  three  pairs  of  glands  called  the  salivary  glands  whose  product 
is  known  as  the  saliva.     These  three  pairs  are  called,  respec- 
tively, the  parotid,  the  submaxillary  and  the  sublingual  glands. 

The  mixed  saliva,  consisting  of  the  secretion  of  all  three  pairs 
of  salivary  glands,  together  with  the  comparatively  insignificant 
amounts  secreted  by  the  various  smaller  glands  of  the  mouth, 
is  a  thin,  colorless,  watery,  slightly  viscid  liquid  .of  alkaline 
reaction.  The  organic  matter  of  the  saliva  includes  a  trace  of 
albumin,  more  or  less  mucus,  and  the  enzym  ptyalin,1  which 
is  its  active  constituent. 

The  saliva  has  both  physical  and  chemical  functions.  The 
presence  of  feed  in  the  mouth,  its  taste,  odor  or  sometimes  even 
sight,  causes  active  secretion  of  saliva,  which  is  mixed  with  the 
feed  in  the  act  of  mastication  and  moistens  and  lubricates  it 
so  that  it  can  be  swallowed.  With  dry  feeding  stuffs,  the 
amount  of  saliva  required  for  this  purpose  is  very  large.  The 
total  secretion  has  been  estimated  at  about  84  pounds  per  day  for 
the  horse  and  at  least  112  pounds  per  day  for  the  ox,  although 
varying  greatly  with  the  dryness  of  the  feed.  Besides  moisten- 
ing and  lubricating  the  feed,  the  saliva  has  also  a  chemical  action 
upon  it.  In  a  slightly  alkaline  medium  and  at  body  tempera- 
ture, the  ptyalin  acts  upon  the  starch  of  the  feed,  converting 
it  ultimately  into  maltose. 

116.  The  stomach.  —  From  the  mouth,  the  feed  in  the  act 
of  swallowing  passes  through  the  esophagus,  or  gullet,  to  the 
stomach  which,  except  in  fowls,  is  the  first  enlargement  of  the 

1  Not  present  in  the  saliva  of  carnivora. 


8o 


NUTRITION  OF  FARM  ANIMALS 


alimentary  canal.  The  horse 'and  hog,  as  well  as  carnivorous 
animals  like  the  dog  and  cat,  have  a  single  stomach  cavity, 
while  ruminants,  such  as  cattle,  sheep  and  goats,  have  a  so- 
called  compound  stomach  consisting,  in  the  farm  animals,  of 
four  divisions,  called  respectively  the  rumen,  or  paunch,  the 


FIG.  9.  —  Sheep's  stomach.     (Hagemann,  Anatomie  und  Physiologic  der 

•        .  Haus-Saugetiere.) 

i,  Rumen.    2,.Reticulum.    3,  Omasum.    4,  Abomasum.    5,  Duodenum.    6,  Esophagus. 

reticulum,  the  omasum,  or  manifolds,  and  the  abomasum,  or 
true  stomach. 

In  reality  the  first  three  divisions  of  the  ruminant  stomach 
are  to  be  regarded  as  dilatations  of  the  esophagus  in  which  the 
feed  undergoes  a  softening  and  fermentation  preliminary  to 
true  gastric  digestion,  while  only  the  fourth  division  is  a  stomach 
in  the  -strict  sense.  In  domestic  fowls  a  similar  dilatation  of 
the  esophagus  at  the  base  of  the  neck  constitutes  the  crop. 

Moreover,  even  the  so-called  single  stomachs  of  the  horse 
and  hog,  while  they  have  but  a  single  cavity,  are  in  reality 
compound  stomachs!  In  the.  case  of  the  horse  three  quite 
distinct  parts  may  be  distinguished,  viz.,  the  left  or  cardiac 
portion,  the  fundus  region  and  the  pyloric  region,  the  two  latter 
having  the  functions  of  the  true  stomach.  In  the  case  of  the 


DIGESTION  AND   RESORPTION 


8l 


FIG.  10.  —  r  Stomach  and  duodenum  of  horse.     (Haglmann,  Anatomic  und 
Physiologic  der  Haus-Saugetiere.) 

Sch.,  Esophagus.    C,  Cardiac  portion.    M,  Fundus.    F,  Pyloric  region.    D,  Duodenum. 

hog  the  cardiac  portion  is  comparatively  small  and  the  remainder 
of  the  organ  is  to  be  regarded  as  constituting  the  stomach 
proper. 

117.  Rumination.  —  In  the  ruminant,  water  and  liquid 
feeds  may  pass  quite 
directly  to  the  aboma- 
sum,  although  as  a 
matter  of  fact,  they 
seem  to  reach  all  four 
divisions  of  the  stomach. 
The  more  bulky  feeds, 
however,  fail  to  pass 
through  the  esophageal 
canal  but  enter  the 
rumen  and  reticulum. 
This  is  especially  the 
case  because  the  rumi- 
nant masticates  its  feed  FlG> 


—  Stomach  of  hog.     (Hagemann,  Ana- 


tomie  und 


1-4,  Fundus.    2,  Cardiac  portion,    s,  Pylorus, 
8,  Duodenum. 


.very  imperfectly  at  the 

time  of  eating.     In  the 

reticulum  and  especially 

in    the   capacious  rumen,   the  partially  masticated   feed   re- 

mains for  some  time  in  contact  with    the  saliva  and  such. 


82  NUTRITION  OF  FARM  ANIMALS 

portion  of  the  drink  as  reaches  this  stomach  and  is  thoroughly 
softened  and  prepared  for  further  action.  The  rumen  is 
so  large  that  it  always  contains  a  considerable  amount  of 
material  and  the  new  feed  when  swallowed  is  more  or  less 
completely  mixed  with  that  already  in  the  rumen  by  the  peri- 
staltic action  of  the  latter,  thus  tending  to  prolong  its  stay. 
The  liquid  or  finely  comminuted  portions  probably  pass  on 
directly  to  the  omasum,  or  manifolds,  and  the  abomasum,  but 
the  bulk  of  the  feed  undergoes  the  process  of  rumination. 

After  the  animal  has  completed  feeding,  and  if  it  is  left  in 
quiet,  small  portions  of  the  feed  are  raised  again  to  the  mouth 
from  the  rumen  and  reticulum  by  contraction  of  these  organs, 
aided  by  the  action  of  the  abdominal  muscles  and  of  the  dia- 
phragm, thoroughly  chewed  and  swallowed  a  second  time. 
This  time  they  pass  to  a  considerable  extent,  though  not 
entirely,  the  esophageal .  canal  and  enter  the  third  stomach, 
the  manifolds,  and  from  this  pass  into  the  fourth  or  true 
stomach. 

The  ruminants  are  animals  which  in  the  wild  state  depend 
on  speed  and  cunning  to  escape  from  their  enemies.  Hence 
it  is  an  advantage  to  them  to  be  able  to  consume  hastily  large 
amounts  of  feed  and  then  to  retire  to  some  safe  concealment 
to  remasticate  and  prepare  it  for  digestion.  Rumination 
also  enables  these  animals  to  utilize  more  thoroughly  coarse 
rough  fodders,  the  long  stay  in  the  paunch  softening  and  fer- 
menting the  material  and  helping  especially  to  destroy  or  dis- 
solve the  carbohydrates  of  the  cell  walls  and  thus  render  the 
cell  contents  accessible  to  the  digestive  fluids. 

118.  The  gastric  juice.  —  The  mucous  membrane  lining  the 
true  stomach  contains  numerous  simple  glands  (tubular  glands) 
differing  in  appearance  in  different  portions  of  the  stomach. 
Those  of  the  fundus  region  contain  two  kinds  of  secreting  cells, 
commonly  designated  as  "  chief  "  and  "  parietal  "  cells.  The 
glands  of  the  pyloric  end  contain  "  chief  "  cells  similar  to  those 
of  the  fundus  glands,  but  only  an  occasional  "  parietal " 
cell.  The  parietal  cells  secrete  as  their  essential  product 
hydrochloric  acid.  The  "  chief "  cells  produce  the  enzym 
pepsin,  or  rather  a  precursor  of  pepsin  called  pepsinogen. 
The  mixed  secretion  of  these  different  glands  constitutes  the 
gastric  juice,  which  is  a  thin,  clear  acid  liquid  having  a 


DIGESTION  AND   RESORPTION  83 

specific  gravity  of  1.005  to  I-°I  and  containing  a  maximum  of 
about  2.5  per  cent  of  solids.  The  combined  action  of  the  pepsin 
and  hydrochloric  acid  of  the  gastric  juice  splits  the  proteins 
of  the  feed  into  derived  proteins,  especially  proteoses  and 
peptones,  and  to  some  extent  into  polypeptids.1  The  hydro- 
chloric acid  of  the  gastric  juice  has  also  an  important  anti- 
septic action  and  likewise  serves  to  dissolve  more  or  less  of 
the  ash  of  the  feed. 

In  addition  to  its  digestive  action  on  proteins,  the  gastric 
juice  contains  an  enzym  which  brings  about  the  coagulation 
of  the  caseinogen  of  milk  —  the  rennet  ferment,  or  chymosin. 
According  to  some  investigators,  chymosin  is  identical  with 
pepsin,  but  the  weight  of  opinion  seems  to  be  in  favor  of  its 
independent  existence. 

119.  The  passage  of  feed  from  the  stomach.  —  The  lower 
or  posterior  end  of  the  stomach  is  closed  by  a  sphincter  muscle 
called  the  pylorus,  which  prevents  the  ingested  feed  from  pass- 
ing into  the  next  division  of  the  alimentary  canal,  the  duodenum, 
or  being  forced  into  it  by  the  contractions  of  the  stomach. 
When  in  the  course  of  gastric  digestion,  however;  the  difference 
between  the  acid  reaction  of  the  stomach  contents  and  the  al- 
kaline reaction  which  normally  prevails  in  the  duodenum 
reaches  a  certain  level,  the  pylorus  relaxes  and  allows  the  per- 
istaltic contraction  of  the  stomach  to  press  a  portion  of  its  acid 
contents  into  the  duodenum.  The  partial  neutralization  of 
the  duodenal  contents  which  results  causes  the  pylorus  to  close 
again  until  the  alkaline  reaction  is  restored,  when  the  cycle  may 
be  repeated. 

The  mechanism  of  this  process  has  been  especially  studied  by 
Cannon  in  carnivora,  but  it  may  be  presumed  that  what  is  true  of  these 
animals  is  also  substantially  true  of  herbivora,  although  experimental 
proof  of  this  is  lacking. 

While  both  protein  and  carbohydrates  undergo  considerable 
digestion  in  the  stomach,  it  is  evident  that  one  important 
function  which  the  stomach  performs  is  that  of  a  receptacle 
which  prevents  too  rapid  passage  of  the  feed  into  the  duodenum 
and  at  the  same  time  initiates  chemical  changes  and  prepares 

1  By  prolonged  peptic  digestion  in  vitro  amino  acids  may  also  be  produced  but 
it  is  not  believed  that  this  occurs  in  natural  digestion. 


84 


NUTRITION  OF  FARM  ANIMALS 


the  feed  for  the  more  vigorous  action  of  the  intestinal  enzyms. 
Moreover,  the  setting  free  of  cell  contents  by  the  fermentation 
of  the  cell  walls  of  vegetable  feeds,  as  well  as  the  liberation  of 
the  fat  of  animal  feeds  by  the  solution  of  the  protein  of  the 
adipose  tissue,  render  these  materials  more  accessible  to  the 
action  of  the  digestive  juices. 

120.   The  small  intestine.  —  On  leaving  the  stomach  through 
the  pylorus,  the  feed  enters  the  small  intestine,  which  may  briefly 


FIG.  12.  —  Intestines  of  cattle.     (Leisering,  Die  Rindviehzucht.) 

be  described  as  a  long,  comparatively  narrow  tube.  Its  average 
length  is,  according  to  Colin,  about  nine  times  that  of  the  body 
in  the  horse,  sixteen  times  in  the  ox  and  sheep  and  eleven  times 
in  the  hog.  It  is  suspended  in  the  abdominal  cavity  by  a  re- 
flection of  the  peritoneum  called  the  mesentery,  and  as  shown 
in  Fig.  1 2  is  much  convoluted.  It  is  commonly  subdivided  into 
duodenum,  jejunum  and  ileum. 

121.  The  coecum.  —  From  the  small  intestine  the  contents  of 
the  digestive  tract  pass,  through  the  ileo-ccecal  valve,,  in  to  the 
ccecum,  which  is  a  diverticulum  of  the  digestive  canal,  the  point 


DIGESTION  AND   RESORPTION 


of  entrance  from  the  small  intestine  and  that  of  exit  into  the 
colon  being  near  together  and  in  the  upper  part  of  the  ccecum. 
Anatomically,  it  might  almost  be  called  a  second  stomach. 
Its  functions,  however,  resemble  those  of  the  first  stomach  of 
ruminants  and  not 
those  of  the  true 
stomach,  the  feed 
stagnating,  so  to 
speak,  in  the 
ccecum  and  under- 
going extensive  f  er- 
mentation  and 
putrefaction.  The 
size  of  the  ccecum, 
in  a  general  way, 
varies  inversely  as 
that  of  the  stom- 
ach. Thus  in  the 
horse  it  is  very 
large,  having  about 
1 6  per  cent  of  the 
total  capacity  of 
the  digestive  canal. 
In  the  ox,  on  the 
other  hand,  it  has 
only  about  3  per 
cent  and  in  the 
sheep  less  than  2.5 
per  cent  of  the  total 
capacity  and  in  the 
hog  about  5.5  per 
cent. 

122.  The  large 
intestine.  --  The 
alimentary  canal  is 
continued  from  the 

ccecum  as  the  large  intestine,  which,  as  its  name  implies,  is  gen- 
erally of  greater  diameter  than  the  small  intestine  but  also 
shorter.  It  is  subdivided  into  the  colon  and  the  rectum  and 
serves  rather  as  a  resorbent  than  as  a  digestive  organ.  The  colon 


FIG.  13. 


Coecum  of  horse.     (Colin,  Physiologic 
comparee  des  Animaux.) 


86  NUTRITION  OF   FARM  ANIMALS 

is  enormously  developed  in  the  horse,  having  about  45  per  cent 
of  the  total  capacity  of  the  digestive  tract,  and  serves,  like  the 
ccecum,  to  continue  the  digestion  of  the  less  soluble  portions 
of  the  feed. 

123.  The   pancreas.  —  In   the   stomach,   the  glands   which 
secrete  the  gastric  juice  are  located  in  the  mucous  lining  of  the 
organ.     In  the  case  of  the  intestines,  the  glands  which  supply 
the  various  digestive  juices,  like  the  salivary  glands  of  the  mouth, 
lie  in  part  entirely  outside  the  alimentary  canal  proper.     One 
of  the  most  important  of  these  is  the  pancreas.     This  is  a  large 
gland  located  near  the  stomach,  liver  and  duodenum,  its  duct 
opening  into  the  latter  either  by  a  common  exit  with  that  of  the 
bile  duct  (horse,  sheep),  or  somewhat  lower  down  (cattle,  swine). 
The  secretory  action  of  the  pancreas,  like  that  of  the  salivary 
and  gastric  glands,  is  intermittent,  the  gland  being  active  only 
when  feed  is  present  in  the  duodenum. 

The  pancreatic  juice  is  a  clear,  viscid  liquid,  having  an  al- 
kaline reaction  due  to  its  content  of  sodium  salts.  It  contains 
in  the  neighborhood  of  eight  to  ten  per  cent  of  solid  matter  and 
has  a  specific  gravity  of  approximately  1.030.  It  differs  from 
other  digestive  juices  in  containing  a  relatively  large  amount 
of  protein.  As  in  the  case  of  all  the  other  digestive  fluids,  the 
essential  active  ingredients  are  enzyms,  of  which  the  pancreatic 
juice  contains  three  in  particular,  viz.,  a  protease,  trypsin,  acting 
upon  the  proteins,  an  amylase,  amylopsin,  acting  upon  starch, 
and  a  lipase,  steapsin,  acting  upon  fats.  Small  amounts  of 
chymosin  and  of  a  lactase  have  also  been  found.  In  the  juice 
as  secreted  by  the  pancreas,  the  trypsin  at  least,  if  not  the  other 
enzyms,  exists  in  the  form  of  a  pro-enzym,  trypsinogen,  which 
is  converted  into  trypsin  ("  activated  ")  after  the  secretion 
reaches  the  duodenum. 

124.  The  liver.  —  This,  the  largest  gland  in  the  body,  is 
located  immediately  below  the  diaphragm  and  lies  chiefly  on 
the  right  side  of  the  body.     It  is  relatively  small  in  ruminants 
and  large  in  the  hog. 

The  liver  has  other  important  functions  in  nutrition,  as  will 
appear  in  Chapter  V,  but  as  related  to  digestion  it  secretes  the 
bile.  This  fluid,  produced  by  the  hepatic  cells,  passes  from 
them  into  the  bile  capillaries,  which  unite  to  form  small  ducts, 
the  latter  finally  coalescing  and  constituting  the  bile  duct.  In 


DIGESTION  AND   RESORPTION  87 

the  horse,  this  empties  directly  into  the  duodenum  a  short 
distance  from  the  stomach.  In  cattle,  sheep  and  swine,  the 
bile  is  stored  up  in  the  gall  bladder,  a  reservoir  from  which  a 
duct  leads  to  the  duodenum. 

The  chief  action  of  the  bile  is  upon  fats  of  the  feed.  To  a 
small  extent,  it  saponifies  them  and  it  also  assists  in  emulsifying 
them.  Its  digestive  action  may,  however,  be  more  conveniently 
considered  along  with  that  of  the  pancreatic  juice  (126,  135). 
In  addition  to  its  action  upon  the  fats,  an  antiseptic  effect  and 
also  a  stimulating  effect  upon  peristalsis  have  been  ascribed  to 
the  bile. 

125.  The   intestinal   juice.  —  In   addition   to   the   external 
glands  (pancreas  and  liver),  already  mentioned,  the  walls  of 
the  small  intestine  contain  a  large  number  of  small  glands  of 
two  kinds,  Brunner's  and  Lieberkiihn's  glands,  which  yield  an 
intestinal  juice  containing  a  number   of   enzyms.     Prominent 
among  these  are  the  invertases  maltase,  sucrase  and  lactase, 
which  act  upon  the  corresponding  disaccharids,  the  maltose  re- 
sulting from  the  digestion  of  starch  being  converted  into  dextrose, 
sucrose  into  a  mixture  of  dextrose  and  levulose,  and  lactose,  in 
suckling  animals  at  least,  into  dextrose  and  galactose. 

There  may  also  be  extracted  from  the  mucous  membrane  of 
the  small  intestine  a  protease  called  erepsin.  This  enzym  does 
not  act  upon  the  native  proteins,  with  the  exception  of  casein, 
but  acts  powerfully  upon  the  derived  proteins  (proteoses  and 
peptones),  hydrolyzing  them  and  breaking  them  down  very 
completely  to  their  constituent  amino  acids.  The  presence  of 
erepsin  has  also  been  demonstrated  in  the  intestinal  juice,  but  its 
action  in  this  case  was  weaker  than  in  the  extracts  of  the  intesti- 
nal wall  and  it  may  be  that  a  portion  of  its  action  in  the  living 
animal  takes  place  within  the  cells  in  which  it  is  produced. 

The  presence  in  the  intestinal  juice  of  an  amylase,  a  lipase 
and  of  ferments  (nucleinases  and  nucleotidases) ,  which  act  upon 
the  nucleic  acids  has  also  been  demonstrated. 

126.  Intestinal  digestion.  —  In  the  duodenum  the  neutraliza- 
tion of  the  acid  material  coming  from  the  stomach  is  effected 
by  the  alkalies  of  the  bile  and  pancreatic  juice,  while  the  bile 
also  precipitates  proteins  and  partly  digested  proteins  in  com- 
bination with  the  bile  acids  and  this  precipitate  carries  down 
with  it  mechanically  the  pepsin  which  is  present.     In  these 


88  NUTRITION  OF   FARM  ANIMALS 

two  ways,  namely  by  neutralization  and  precipitation,  the  pep- 
sin is  prevented  from  digesting  the  enzyms  of  the  pancreatic 
juice  and  bile,  an  action  which  would  otherwise  take  place,  since 
these  enzyms  appear  to  be  substantially  protein  in  their  nature.1 
In  the  small  intestine,  the  neutralized  contents  of  the  stomach 
are  subjected  to  the  combined  action  of  the  pancreatic  juice, 
the  bile  and  the  intestinal  juice,  while  they  are  moved  along 
through  the  successive  divisions  of  the  small  and  large  intestines 
by  means  of  the  peristaltic  movements  of  the  latter.  These 
movements  serve  also  to  mix  the  contents  of  the  intestines 
and  to  bring  them  into  intimate  contact  with  the  intestinal 
walls. 

The  fats  of  the  feed,  under  the  action  of  the  steapsin  of  the 
pancreatic  juice,  undergo  a  cleavage  into  glycerol  and  fatty 
acids  and  this  change  is  considerably  accelerated  by  the  bile, 
which  also  aids  in  emulsifying  the  fats  and  so  exposing  vastly 
more  surface  to  the  action  of  the  enzyms.  The  fatty  acids 
thus  set  free  unite  to  a  greater  or  less  extent  with  the  alkali  of 
the  pancreatic  juice  and  bile,  forming  soaps,  while  both  soaps 
and  free  fatty  acids  are  soluble  in  bile  in  the  presence  of  sodium 
carbonate.  The  presence  of  soaps  in  solution  also  aids,  as  was 
pointed  out  in  Chapter  I,  in  producing  a  permanent  emulsion 
of  the  fats. 

Starch,  if  any  escapes  digestion  in  the  stomach,  is  acted  upon 
by  the  pancreatic  amylopsin  substantially  in  the  same  manner 
as  by  the  ptyalin  of  the  saliva  but  much  more  energetically, 
yielding  maltose,  while  both  maltose  and  any  other  disaccharid 
present  in  the  feed  are  acted  upon  by  the  invertases  of  the  in- 
testinal juice,  yielding  monosaccharids. 

Any  proteins  which  escape  digestion  in  the  stomach,  and 
likewise  the  proteoses  and  peptones  resulting  from  peptic  di- 
gestion, are  hydrolyzed  by  trypsin  and  erepsin  much  more 
energetically  than  by  pepsin  and  yield  not  only  proteoses  and 
peptones,  but  a  whole  series  of  progressively  simpler  poly- 
peptids  and  finally  are  largely  or  wholly  split  up  into  their 
constituent  amino  acids. 

1  The  foregoing  statements  describe  what  takes  place  when  the  materials  are 
mixed  in  the  laboratory.  The  actual  importance  of  the  precipitation  of  the  pepsin 
in  the  intestine  is  somewhat  in  doubt. 


DIGESTION  AND   RESORPTION  89 

§  2.  THE  CHEMISTRY  OF  DIGESTION 

127.  Digestion  a  chemical  process.  —  The  foregoing  para- 
graphs have  dealt  chiefly  with  those  more  general  facts  regard- 
ing the  organs  of  digestion  which  are  necessary  for  an  under- 
standing of  their  functions  and  only  incidentally  and  in  outline 
with  the  chemical  processes  involved.     It  is  now  time  to  revert 
to  the  statement  made  at  the  beginning  of  the  chapter,  namely, 
that  digestion  is  the  first  step  in  the  conversion  of  feed  sub- 
stances into  body  substances,  and  specifically  in  the  case  of  farm 
animals  the  conversion  of  vegetable  into  animal  substances. 
These,  however,  are  chemical  transformations  and  from  this 
point  of  view  a  knowledge  of  the  structure  of  the   digestive 
apparatus  is  of  significance  chiefly  as  an  aid  to  the  understanding 
of  these  processes.   Tn  taking  up  this  aspect  of  the  subject,  it 
will  be  convenient  to  consider  the  three  chief  groups  of  nutrients 
separately. 

The  digestion  of  carbohydrates 

By  far  the  larger  proportion  of  the  carbohydrates  contained 
in  the  feed  of  farm  animals  consists  of  polysaccharids,  especially 
starch,  cellulose  and  the  various  pentosans  and  hexo-pentosans. 
The  disaccharids,  especially  sucrose  and  lactose,  probably  stand 
next  in  importance,  while  comparatively  small  amounts  of 
monosaccharids  are  consumed. 

128.  Cellulose.  —  The  cellulose  of  feeding  stuffs  was  long 
assumed  to  be  indigestible.     Haubner  was  the  first  to  show  the 
incorrectness  of  this  assumption  and  to  prove  that  even  the 
cellulose  of  such  substances  as  paper  pulp  and  sawdust,  as  well 
as  that  of  ordinary  feeds,  was  digested  by  cattle.     The  subse- 
quent investigations  of  Henneberg  and  Stohmann   (158,  707) 
showed  that  the  crude  fiber  of  feeding  stuffs  was  digested  to  a 
considerable  extent  by  cattle,  and  sheep,  and  later  digestion  ex- 
periments have  proved  this  to  be  true  not  only  of  ruminants 
but  to  a  varying  degree  of  other  animals,  both  herbivora  and 
omnivora,  including  domestic  fowls.     Even  man  is  capable  of 
digesting   the  tenderer  forms  of   cellulose  to   a   considerable 
extent. 

None  of  the  digestive  enzyms  of  the  higher  animals,  however, 
have  been  shown  to  have  any  action  upon  cellulose  and  the  small 


go  NUTRITION  OF  FARM  ANIMALS 

amounts  of  cellulose-dissolving  enzyms  (cytases)  found  in  some 
feeds  appear  quite  inadequate  to  account  for  its  solution,  so 
that  the  manner  of  its  digestion  was  long  a  puzzle.  The  in- 
vestigations of  Wildt l  in  1874  upon  the  digestive  process  in 
sheep,  however,  showed,  as  Zuntz  2  subsequently  pointed  out, 
that  the  solution  of  cellulose  occurs  chiefly  in  those  portions  of 
the  alimentary  canal  where  the  feed  stagnates,  —  that  is,  in 
the  paunch  of  the  ruminant  and  in  the  ccecum  and  colon. 
This  fact  tended  to  confirm  the  view  already  advanced  that  the 
solution  of  cellulose  in  the  digestive  tract  was  due  to  a  process  of 
fermentation,  and  this  hypothesis  also  served  to  explain  the 
presence  of  methane  and  hydrogen  in  the  digestive  tract.  Tap- 
peiner,3  however,  seems  to  have  been  the  first  to  show  ex- 
perimentally that  the  disappearance  of  cellulose  in  the  digestive 
tract  is  effected  by  a  fermentation  brought  'about  by  the  micro- 
organisms inhabiting  the  alimentary  canal. 

Tappeiner's  conclusions  have  been  fully  confirmed  by  more 
recent  investigations,  notably  those  of  Markoff 4  in  Zuntz's 
laboratory,  while  Kellner  5  has  shown  that  the  consumption  of 
crude  fiber  (straw  pulp)  by  cattle  causes  a  marked  increase  in 
the  amount  of  methane  eliminated.  In  the  light  of  these 
results  it  may  be  regarded  as  established  that  the  disappearance 
of  cellulose  during  its  passage  through  the  alimentary  canal  of 
herbivora  is  not  due  to  a  digestion  in  the  sense  of  a  simple  hydro- 
lytic  cleavage,  like  that  of  starch  or  protein,  but  to  a  destructive 
fermentation.  The  products  of  this  fermentation  are  large  quan- 
tities of  carbon  dioxid  and  methane  and  small  amounts  of  hydro- 
gen, which  are  excreted,  and  various  organic  acids  of  the  aliphatic 
series  which  combine  with  the  alkalies  of  the  saliva  or  other 
digestive  fluids.  The  salts  thus  formed  are  resorbed  and  consti- 
tute the  sole  contribution  which  cellulose  makes  to  the  nutrition  of 
the  body.  The  principal  acids  formed  appear  to  be  acetic  and 
butyric,  although  others  are  also .  present.  In  ruminants,  the 
chief  seat  of  this  fermentation  is  the  capacious  first  stomach, 
while  in  the  horse,  with  his  relatively  small,  simple  stomach, 
it  takes  place  principally  or  wholly  in  the  enormous  ccecum  and 
colon. 

1  Jour.  Landw.,  22  (1874),  i.  2  Landw.  Jahrb.,  8  (1879),  101. 

3Ztschr.  Biol.,  20  (1884),  52. 

4  Biochem.  Ztschr.,  34  (IQII),  211 ;   57  (1913),  i. 

5  Landw.  Vers.  Stat.,  53  (1900),  193,  300. 


DIGESTION  AND   RESORPTION  91 

129.  Pentosans.  —  The  pentosans  are  widely  distributed 
in  the  vegetable  kingdom  and  appear  to  be  contained  chiefly 
or  wholly  in  the  cell  walls  of  plants,  probably  in  combination 
to  a  greater  or  less  extent  with  hexosans.  If  the  ordinary 
methods  of  feeding  stuffs  analysis  are  followed,  both  the  crude 
fiber  and  nitrogen-free  extract  contain  them  (109,  110). 

Stone,1  who  was  the  first  to  show  that  they  were  digestible, 
found  a  percentage  digestibility  of  about  60  for  the  pentosans 
in  the  ordinary  feed  of  the  rabbit.  Later,2  in  conjunction  with 
Jones,  he  showed  that  in  14  different  samples  of  roughages 
from  48  to  90  per  cent  of  the  pentosans  were  digested  by  sheep, 
while  in  mixed  rations  the  corresponding  figures  were  from  46 
to  71  per  cent.  Weiske3  about  the  same  time  obtained  similar 
results  in  experiments  with  sheep  and  rabbits.  The  digesti- 
bility of  pentosans  has  been  fully  confirmed  by  later  experiments. 

But  while  pentosans  are  digestible,  or  at  least  disappear  in 
the  digestive  tract,  the  manner  of  their  digestion  is  not  cer- 
tainly known.  Up  to  the  present  time  no  enzyms  have  been 
discovered  either  in  the  digestive  organs  or  elsewhere,  which 
have  been  proved  to  be  capable  of  hydrolyzing  them.  On  the 
other  hand,  however,  the  pentosans  are  attacked  by  bacteria 
much  like  other  carbohydrates  and  yield  similar  products, 
especially  the  acids  of  the  aliphatic  series.  That  the  pentosans 
are  to  a  considerable  extent  subject  to  the  methane  fermenta- 
tion in  the  digestive  tract  seems  clear  from  Kellner's  investi- 
gations upon  straw  pulp  (128) ,  in  which  over  one- third  of  the  di- 
gested organic  matter  consisted  of  pentosans,  so  that  it  is  difficult 
to  resist  the  conclusion  that  these,  as  well  as  the  cellulose,  under- 
went fermentation.  Moreover,  in  a  large  number  of  similar 
experiments,  the  methane  fermentation  has  been  found  in  a 
general  way  to  be  proportional  to  the  total  digestible  crude 
fiber  and  nitrogen-free  extract,  including  the  pentosans.  Of 
course  these  results  do  not  preclude  the  possibility  of  a  hy- 
drolysis of  the  pentosans  in  the  digestive  tract,  converting  them 
into  pentose  sugars,  but  as  yet  there  is  no  direct  evidence  that 
such  a  process  takes  place.  If  it  does  not,  then  the  products  of 
the  digestion  of  the  pentosans  are  substantially  the  same  as 
those  from  cellulose. 

1  Amer.  Chem.  Jour.,  14  (1892),  9.  2  Agricultural  Science,  7  (1893),  6. 

3Ztschr.  Physiol.  Chem.,  20  (1895),  489,    ' 


92  NUTRITION  OF  FARM  ANIMALS 

130.  Hemicelluloses.  —  What    is    true    specifically    of    the 
pentosans  appears   to  hold  also  for  the  reserve  carbohydrates 
of   the   cell   wall  —  the   so-called   hemicelluloses    (18)  —  as   a 
whole.     No  animal  enzyms  are  known  which  hydrolyze  the 
galactans,  levulans,  etc.,  or  which  break  up  their  union,  if  it 
exists,  with  the  pentosans,  but  nevertheless   these  substances 
disappear  in  part  in  the  digestive  tract  of  herbivora.     Pending 
more  exact  knowledge  on  this  point,  the  assumption  seems 
warranted  that  they  as  well  as  the  pentosans  undergo  bacterial 
fermentation  and  yield  substantially  the  same  products. 

131.  Starch.  —  The  first  agent  to  act  upon  starch  is  the 
ptyalin  of  the  saliva  (115).     As  is  the  case  with  the  other 
enzyms,  ptyalin  has  never  been  isolated,  but  its  effects  and  the 
conditions  governing  its  action  have  been  extensively  studied, 
in  part  owing  to  the  ease  with  which  saliva  can  be  procured. 
The  most  important  of  these  conditions  are  that  ptyalin  acts 
most  efficiently  in  the  neighborhood  of  40°  C.,  that  is,  at  about 
blood  temperature,  in  a  neutral  solution,  while  more  than  a 
trace  of  free  acid  or  alkali  inhibits  its  action.     To  acids  or  al- 
kalies combined  with  proteins,  even  though  they  show  an  acid 
or  alkaline  reaction  to  ordinary  indicators,  ptyalin  is  much  less 
sensitive  and  it  is  also  less  sensitive  to  organic  than  to  inorganic 
acids.     In  brief,  the  action  of  ptyalin  is  inhibited  by  a  very  low 
concentration  of  either  hydrogen  or  hydroxyl  ions. 

The  action  of  ptyalin  on  starch  consists  of  a  succession  of 
cleavages  and  hydrations  resulting  in  the  formation  of  the  various 
dextrins  (24)  and  finally  of  sugar.  With  cooked  starch,  the 
action  is  fairly  rapid ;  upon  raw  starch  ptyalin  acts  more  slowly, 
the  rate  varying  somewhat  with  the  kind  of  starch  and  being 
apparently  determined  by  the  degree  of  resistance  of  the  cellulose 
envelope  of  the  starch  grains.  Chemically,  the  action  is  analo- 
gous to  that  of  acids,  but  is  less  vigorous  and  is  not  carried  so  far. 
The  action  of  acids  yields  dextrose  as  a  final  product ;  that  of 
ptyalin  is  usually  stated  to  stop  with  the  production  of  maltose.1 

The  action  of  ptyalin  in  the  mouth  is  necessarily  very  brief. 
In  the  stomach  the  feed  comes  into  contact  with  the  gastric 
juice  containing  free  hydrochloric  acid.  At  first,  this  acid 
combines  with  the  proteins  contained  in  the  feed,  but  as  soon 

1  Carlson  and  Luckhart  (Amer.  Jour.  Physiol.,  23  (1908-9),  149)  state  that  both 
ptyalin  and  amylopsin  produce  dextrose  from  starch. 


DIGESTION  AND   RESORPTION  93 

as  more  than  a  trace  of  free  acid  accumulates,  or  to  speak  more 
exactly,  as  soon  as  the  concentration  of  the  hydrogen  ions  ex- 
ceeds a  certain  small  limit,  the  action  of  the  ferment  is  not  only 
inhibited,  but  the  ptyalin  is  digested  by  the  pepsin. 

This,  however,  is  far  from  happening  immediately  upon  the 
entry  of  the  feed  into  the  stomach.  The  secretion  of  the  gastric 
juice  requires  a  certain  length  of  time.  Moreover,  the  contents 
of  the  stomach  are  semi-solid  rather  than  liquid  and  while  the 
muscular  contractions  of  the  stomach  serve  to  mix  the  feed  to 
some  extent,  this  effect  is  less  than  is  often  assumed.  Frozen 
sections  of  animals  to  which  variously  colored  feeds  have 
been  given  show  the  contents  of  the  stomach  to  be  distinctly 
stratified  some  time  after  the  ingestion  of  feed.  Furthermore, 
the  gastric  juice  is  secreted  only  in  the  pyloric  portion  of 
the  stomach  (116).  Time  is  required,  therefore,  for  the 
acid  to  penetrate  and  acidify  the  whole  mass  and  conse- 
quently the  action  of  the  ptyalin  may  continue  for  a  con- 
siderable period. 

Extensive  investigations,  especially  by  Ellenberger  and 
Hofmeister,  upon  gastric  digestion  in  the  horse  and  hog  have 
demonstrated  that  in  these  animals  the  action  of  the  saliva  in 
the  stomach  upon  the  starch  of  the  feed  plays  an  important 
part  in  digestion.  In  the  horse  (116),  the  left  end  of  the  stomach 
is  really  a  dilation  of  the  esophagus.  In  the  hog,  while  nearly 
the  entire  surface  of  the  stomach  is  lined  with  mucous  membrane, 
the  left-hand  end  contains  no  peptic  glands.  When  the  stomach 
is  filled  with  feed,  therefore,  it  is  evident  that  the  action  of  the 
hydrochloric  acid  will  begin  along  the  walls  of  the  fundus  of 
the  stomach  and  only  gradually  spread  to  the  rest  of  the  con- 
tents. It  is  true  that  lactic  fermentation  usually  sets  in  during 
this  period,  aiding  to  acidify  the  stomach  contents  but,  as 
already  stated,  ptyalin  is  less  sensitive  to  organic  than  to 
inorganic  acids.  It  has  been  found  that  the  solution  of  starch 
may  continue  to  a  greater  or  less  extent  for  as  much  as  four  or 
five  hours  both  in  the  horse  and  hog.  •  In  ruminants,  the  con- 
ditions are  even  more  favorable  for  salivary  action,  since  the 
feed  remains  in  contact  with  the  saliva  in  the  rumen  for  a  con- 
siderable time,  the  contents  of  this  stomach  being  maintained 
slightly  alkaline  by  the  large  amount  of  saliva  secreted  by  these 
animals  (115).  It  may  be  assumed,  therefore,  in  spite  of  the 


94  NUTRITION  OF  FARM   ANIMALS 

fact  that  the  saliva  of  ruminants  contains  but  little  ptyalin,  that 
a  considerable  digestion  of  starch  is  effected. 

In  the  duodenum,  any  starch  not  digested  in  the  stomach, 
as  well  as  any  dextrins,  etc.,  produced  by  the  action  of  the 
ptyalin,  are  subjected  to  the  action  of  the  amylopsin  of  the 
pancreatic  juice.  This  enzym,  if  not  identical  with  ptyalin,  is 
very  similar  to  it  but  appears  to  act  more  energetically.  As 
in  the  case  of  ptyalin,  the  final  product  of  its  action  is  maltose.1 

The  further  fate  of  the  maltose  resulting  from  the  digestion 
of  starch  is  more  conveniently  considered  along  with  that  of 
other  disaccharids  in  a  succeeding  paragraph. 

132.  Fermentation  of  starch.  —  The  organisms  producing 
the  methane  fermentation  in  the  digestive  tract  were  believed 
by  Tappeiner  to  attack  cellulose  specifically  and  not  to  act 
upon  other  carbohydrates.  As  regards  ruminants,  however, 
this  has  been  shown  to  *be  an  error.  In  G.  Klihn's  2  extensive 
respiration  experiments  with  cattle  upon  the  formation  of  fats 
from  carbohydrates,  considerable  amounts  of  starch  were  added 
to  basal  rations.  Invariably  this  resulted  in  an  increased  ex- 
cretion of  methane.  Moreover,  there  was  no  increase,  but  on 
the  other  hand,  more  or  less  decrease  in  the  amount  of  crude 
fiber  digested,  showing  that  the  additional  methane  must  have 
had  its  source  in  the  starch  consumed.  This  conclusion  is 
confirmed  by  the  fact  that  the  total  excretion  of  methane  was 
quite  closely  proportional  to  the  sum  of  the  digested  crude 
fiber  and  nitrogen-free  extract.  On  the  average  four  parts  of 
methane  were  produced  for  each  one  hundred  parts  of  starch 
digested.  Kellner's  subsequent  investigations 3  have  fully 
confirmed  these  results,  although  giving  a  lower  average,  viz., 
3.07  parts  of  methane  per  one  hundred  parts  of  digestible 
starch.  Moreover,  Kellner's  investigations  have  shown  that 
the  methane  fermentation  is  not  confined  to  cellulose  and 
starch  but  that,  as  already  indicated,  the  complex  of  compounds 
grouped  under  the  head  of  nitrogen-free  extract,  including  the 
sugars,  is  subject  to  this  process.  His  experiments  also  show 
that  the  proportion  of  methane  produced  is  somewhat  variable, 
depending  upon  conditions  not  yet  fully  investigated. 

As  already  stated  (128),  the  chief  seat  of  fermentation  in  the 

1  See  footnote  on  p.  92.  2  Kellner;  Landw.  Vers.  Stat,  44  (1894),  257. 

3Landw.  Vers.  Stat.,  53  (1900),  423. 


DIGESTION  AND   RESORPTION  95 

horse  is  the  coecum  and  colon.  Before  the  feed  reaches  these, 
however,  it  has  been  acted  upon  by  the  amylases  of  the  saliva 
and  the  pancreatic  juice  and  its  starch  and  soluble  carbohy- 
drates pretty  thoroughly  extracted.  Consequently,  the  meth- 
ane production  of  the  horse  is  substantially  at  the  expense 
of  the  crude  fiber  of  his  feed,  although  if  starch  for  any  reason 
escapes  digestion  and  reaches  the  ccecum  it  is  doubtless  also 
attacked  by  the  bacteria. 

133.  The  disaccharids.  —  At  first  thought,  it  would  seem 
that  the  carbohydrates  of  this  group  need  no  digestive  change, 
since  they  are  already  soluble  and  diffusible  and  seemingly  ready 
to  pass  into  the  circulation.     But  while  this  is  true,  they  are 
not  assimilable  by  the  organism.     Disaccharids  are  nowhere 
found  in  the  normal  body  fluids  and  if  injected  into  the  circu- 
lation in  any  considerable  amount  are  voided  in  the  urine.     In 
other  words,  the  disaccharids  are  treated  in  the  organism  as 
foreign  substances  which  the  cells  cannot  use. 

In  the  small  intestine  the  disaccharids  are  inverted,  that  is, 
hydrolyzed  to  monosaccharids.  Cane  sugar  taken  in  the  food 
appears  to  be  inverted  to  some  extent  by  the  acid  of  the  gastric 
juice,  but  the  principal  action  is  by  the  inverting  enzym  sucrase 
of  the  intestinal  juice,  which  splits  up  the  cane  sugar  into  dex- 
trose and  levulose.  Similarly,  the  maltose  resulting  from  the 
digestion  of  starch  is  split  up  by  the  maltase  of  the  intestinal 
juice,  yielding  dextrose,  while  lactose,  at  least  in  suckling  animals, 
is  split  up  by  lactase  into  dextrose  and  galactose.  These  in- 
versions appear  to  take  place  to  a  considerable  extent  in  the 
epithelial  cells  lining  the  intestines,  and  this  seems  to  be  the 
normal  method  of  assimilation  of  lactose  in  many  mature  ani- 
mals. The  epithelial  cells  are  also  stated  to  convert  levulose 
and  galactose  into  dextrose. 

Finally  it  should  be  added  that  the  sugars,  like  other  carbo- 
hydrates, may  undergo  the  methane  fermentation  in  the  first 
stomach  of  ruminants. 

The  digestion  of  fats 

134.  Emulsification.  —  As  already  indicated,   the  digestion 
of   fats   includes   two   processes,   namely,    emulsification   and 
saponification,  effected  chiefly  by  the  action  of  the  bile   and 


96  NUTRITION  OF  FARM  ANIMALS 

pancreatic  juice.  The  two  processes  go  hand  in  hand.  As 
explained  in  Chapter  I,  the  presence  of  free  fatty  acids  favors 
the  formation  of  a  permanent  emulsion.  As  there  noted,  most 
native  fats  contain  small  amounts  of  such  acids  which  exist 
dissolved  in  the  natural  fat.  Furthermore,  there  seems  to  be 
good  evidence  that  some  cleavage  of  fat  into  fatty  acids  and 
glycerol  takes  place  in  the  stomach  of  carnivora,  while  the  di- 
gestion of  protein  in  the  stomach  helps  to  liberate  any  enclosed 
fat.  When  the  acid  fats  come  in  contact  with  the  alkaline 
pancreatic  juice,  the  molecules  of  the  free  acid  in  solution  are 
saponified  and  in  this  way  the  mass  of  fat  is  broken  up  into  an 
emulsion.  The  action  of  the  steapsin  of  the  pancreatic  juice, 
which  splits  fat  into  glycerol  and  ^fatty  acids,  would  obviously 
tend  to  aid  in  the  emulsification,  while,  on  the  other  hand,  the 
latter,  by  vastly  increasing  the  amount  of  surface  exposed  by  the 
fats,  tends  to  aid  the  action  of  the  enzyms. 

135.  Saponification.  —  The  saponification  of  fat   is   accom- 
plished essentially  by  the  lipase  steapsin  of  the  pancreatic  juice. 
As  just  noted,  the  saponification  is  facilitated  by  the  previous 
emulsification,  while  the  presence  of  the  bile  is  also  an  important 
factor.     It  is  claimed  that  the  presence  of  bile  is  necessary  to 
activate  the  steapsin,  while  it  has  also  been  shown  that  the 
cleavage  of  the  fats  is  much  accelerated  by  the  presence  of  bile, 
the  effect  being  ascribed  to  the  lecithins  which  it  contains.     The 
presence  of  bile  also  assists  in  the  process  of  digestion  by  its 
power   of   dissolving   large   quantities   of   fatty   acids   and  of 
their  calcium  and  magnesium  soaps.     It  appears  also  that  the 
bile  aids  in  some  way  in  the  resorption  of  the  fat,  but  just  how 
is  not  clear. 

Fats  do  not  seem  to  be  fermented  to  any  extent  in  the  diges- 
tive tract  and  when  administered  to  cattle  in  the  form  of  emul- 
sions have  been  found  to  produce  no  effect  upon  the  excretion 
of  methane.  When  given  in  substance,  they  have  in  some  in- 
stances had  the  effect  of  diminishing  the  excretion  of  that  gas. 

The  digestion  of  the  proteins  and  non-proteins 

136.  Peptic  digestion.  —  In  digestion  the  proteins  are  first 
subjected  in  the  stomach  to  the  action  of  the  pepsin  and  hy- 
drochloric acid  of  the  gastric  juice. 


DIGESTION  AND   RESORPTION  97 

The  products  of  peptic  digestion  are  usually  substances  be- 
longing to  the  group  of  derived  proteins  (58,  59).  The  first 
product  or  products  are  substances  called  metaproteins,  or, 
according  to  the  older  terminology,  syntonin  or  acid  proteins. 
By  still  further  action  there  is  formed  a  succession  of  proteoses 
and  from  these,  by  subsequent  cleavage,  peptones.  Undoubt- 
edly the  products  resulting  from  peptic  digestion  contain  a 
large  number  of  chemical  individuals  but  for  the  present  pur- 
pose it.  is  sufficient  to  say  that  the  action  of  pepsin  and  hydro- 
chloric acid  gives  rise  to  the  formation  of  a  series  of  progres- 
sively simpler,  more  soluble  and  more  diffusible  substances.  In 
natural  digestion,  the  action  extends  in  the  main  only  as  far 
as  the  production  of  peptones,  although  polypeptids  seem  to 
be  also  formed  to  some  extent.  Amino  acids  are  not  found 
among  the  products  of  natural  peptic  digestion,  although  they 
may  be  produced  by  the  long  continued  action  of  pepsin-hy- 
drochloric acid  in  artificial  digestion. 

The  conjugated  proteins  are  split  into  their  two  constituents 
and  the  protein  portion  is  then  acted  upon  like  other  proteins. 
The  gastric  juice  has  no  action  upon  the  nucleic  acids  of  the 
nucleoproteins. 

137.  Tryptic  digestion.  —  In  the  duodenum,  the  proteins 
and  the  products  of  their  peptic  digestion  are  subjected  to  the 
action  of  the  trypsin  of  the  pancreatic  juice.  This  is  produced 
in  the  pancreas  in  the  form  of  a  pro-ferment  or  zymogen,  called 
trypsinogen.  The  presence  of  pancreatic  juice  in  the  duodenum 
stimulates  the  glands  of  the  latter  to  the  production  of  the  in- 
testinal juice  which  Pawlow  has  found  to  contain  a  substance, 
enterokinase,  which  activates  the  trypsinogen,  or  converts  it  into 
trypsin,  in  some  unknown  manner. 

The  action  of  trypsin,  like  that  of  pepsin,  has  been  largely 
studied  in  laboratory  experiments  either  with  extracts  of  the 
pancreas  or  with  its  secretion  as  obtained  from  fistulae.  Tryp- 
sin, especially  in  a  neutral  or  alkaline  solution,  acts  upon  pro- 
teins substantially  in  the  same  manner  as  pepsin,  causing  a 
hydrolytic  cleavage  and  producing  at  first  proteoses  and  pep- 
tones. It  acts  much  "more  energetically  than  pepsin,  however, 
and  carries  the  cleavage  much  further.  The  action  of  pepsin 
substantially  stops  with  the  production  of  peptones.  Trypsin, 
on  the  other  hand,  produces  a  relatively  large  amount  of  the 


98  NUTRITION  OF  FARM  ANIMALS 

simple  amino  acids  out  of  which  the  protein  molecule  is  built 
up.  Even  the  most  prolonged  action  of  trypsin,  however, 
leaves  a  considerable  residue  in  which  no  free  amino  acids  are 
found  but  which  on  hydrolysis  with  strong  mineral  acids  yields 
them  in  abundance. 

Conjugated  proteins  seem  to  be  acted  upon  by  trypsin  in  the 
same  manner  as  by  pepsin  but  much  more  energetically. 

138.  Erepsin.  —  The  presence   of   a  proteolytic   enzym  in 
the  intestinal  juice  and  in  the  epithelial  cells  of  the  small  intes- 
tine has  already  been  noted  (135) .     This  enzym  does  not  act  on 
unaltered  proteins,  with  the  exception  of  casein,  but  it  hy- 
drolyzes  proteoses  and  peptones  energetically,  yielding  crystal- 
line cleavage  products.     It  is  of  special  interest  to  note  that, 
according  to  Cohnheim,1  erepsin  is  capable  of  effecting  the 
cleavage  of  that  part  of  the  protein  molecule  which  is  not  at- 
tacked by  pepsin  and  trypsin  and  that  in  artificial  digestion 
experiments   almost   complete   conversion  into  comparatively 
simple  crystalline  products  may  be  obtained  in  a  relatively  short 
time. 

139.  Extent   of   protein   cleavage   in   natural    digestion.  — 
When  it  was  first  shown  by  Kiihne  and  Chittenden  that  the 
action  of  trypsin  upon  proteins  yielded  among  other  products 
such  simple  crystalline  substances  as  leucin  and  tyrosin,  com- 
paratively little  importance  was  attached  to  the  fact  from  the 
physiological  standpoint.     While  the  fact  was  interesting  as 
throwing  light  upon  the  chemical  structure  of  the  proteins,  it 
was  believed  that  in  natural  digestion  the  soluble  proteoses  and 
peptones  were  promptly  removed  from  the  digestive  tract  by 
resorption  and  that  at  most  but  a  small  proportion  of  the  feed 
protein  underwent  any  profound  cleavage.     This  belief  was 
the  stronger  because  it  was  believed  that  only  proteins  or  their 
slightly  altered  derivatives,  the  proteoses  and  peptones,  could 
supply  the  demands  of  the  organism  for  proteins.     Whatever 
protein  was  broken  down  into  crystalline  products  was  looked 
upon  as  wasted.     With  the  progress  of  investigation,  however, 
it  has  become  increasingly  clear  that   the  processes   of    hy- 
drolytic  cleavage  go  further  and  play  a  much  more  important 
part  than  was  formerly  supposed.     While  it  is  admitted  that 
peptones,  or  even  soluble  proteins,  may  be  resorbed,  the  weight 

3  Ztschr.  Physiol.  Chem.  49  (1906),  64;  51  (1907),  415. 


DIGESTION  AND   RESORPTION  99 

of  opinion  is  that,  as  a  matter  of  fact,  proteins  are  largely  re- 
sorbed  in  the  form  of  comparatively  simple  cleavage  products ; 
not  necessarily  in  every  case  as  simple  amino  acids  but  at  least 
in  the  form  of  comparatively  simple  peptids. 

The  nucleic  acids  derived  from  the  peptic  or  tryptic  diges- 
tion of  the  nucleoproteins  are  split  by  the  nucleases  of  the  in- 
testinal juice  into  mononucleotids  and  these  again  by  the 
nucleotidases  of  the  same  secretion  into  nucleosids  (53).  No 
digestive  enzyms  attacking  the  latter  class  of  compounds  are 
known,  but  they  are  split  to  some  extent  by  intestinal  bacteria 
into  pentoses  and  purin  or  pyrimidin  bases.  Furthermore,  it  has 
been  found  that  extracts  of  the  intestinal  mucous  membrane 
(epithelial  cells)  possess  the  power  of  bringing  about  the  same 
cleavages  which  are  accomplished  by  the  enzyms  of  the  in- 
testinal juice,  and  in  addition  are  able  to  split  the  resulting 
nucleosids  into  pentose  and  base.  It  appears,  then,  that  the 
final  digestive  products  of  the  nucleic  acids  are,  as  in  the  case 
of  the  simple  proteins,  relatively  simple  substances,  viz.,  phos- 
phoric acid,  pentoses,  and  purin  and  pyrimidin  bases. 

140.  Putrefaction  of  proteins.  —  Attention  has  already  been 
called,  in  connection  with  the  digestion  of  the  carbohydrates, 
to  the  bacterial  flora  of  the  digestive  tract.  The  carbohy- 
drates, as  was  shown,  are  acted  upon  chiefly  by  the  organisms 
producing  the  methane  fermentation.  Proteins  and  their  de- 
rivatives, on  the  other  hand,  have  been  shown  by  Kellner  to 
contribute  practically  nothing  to  this  fermentation  in  the  case 
of  cattle.  They  are,  however,  especially  subject  to  the  action 
of  the  organisms  producing  putrefaction.  The  action  of  such 
organisms  is  prevented  in  the  stomach  by  the  hydrochloric  acid 
of  the  gastric  juice.  In  the  small  intestine  they  become  more 
active,  especially  as  the  feed  reaches  the  lower  portion,  while 
their  activity  lessens  again  as  the  lower  portion  of  the  large  in- 
testine is  reached,  owing  to  the  progressive  resorption  of  water 
from  the  intestinal  contents.  The  characteristic  products  of 
the  putrefaction  are  ammonia  and  certain  aromatic  compounds 
derived  from  the  heterocyclic  components  of  the  proteins  (47). 

The  aromatic  products  of  putrefaction  (indols  and  phenols) 
are  found  in  part  in  the  feces  but  are  in  large  part  resorbed. 
They  cannot,  however,  be  utilized  by  the  organism  but,  on  the 
contrary,  are  poisonous  and  are  therefore  combined  with  other 


100  NUTRITION  OF  FARM  ANIMALS 

substances  which  render  them  innocuous.  In  particular,  they 
unite  with  sulphates  to  form  the  so-called  ether-sulphates  which 
are  excreted  in  the  urine.  The  amount  of  these  substances  in 
the  urine  furnishes  a  convenient  index  to  the  extent  of  intestinal 
putrefaction. 

141.  The  non-proteins.  —  As  ordinarily  determined  (61, 
106),  the  non-proteins  constitute  a  group  of  nitrogenous  sub- 
stances soluble  in  water,  many  of  which  are  identical  with  or 
closely  related  to  the  final  products  of  the  digestion  of  the 
proteins.  Accordingly,  they  have  generally  been  assumed  to 
be  ready  for  resorption  without  further  action  by  the  digestive 
juices  and  therefore  to  be  entirely  digestible. 

It  has  been  shown,  however,  that,  in  ruminants  at  least,  the 
matter  is  by  no  means  so  simple  as  the  mere  resorption  of  water- 
soluble  substances.  In  the  capacious  first  stomach  of  these 
animals,  the  non-proteins  play  an  important  role  as  a  supply 
of  nitrogenous  food  for  the  organisms  which  are  so  abundant 
there.  This  has  several  consequences. 

In  the  first  place,  it  appears  that  these  soluble  compounds 
are  more  readily  attacked  and  utilized  by  the  organisms  than 
are  the  true  proteins  of  the  feed.  The  presence  of  non-proteins, 
therefore,  tends  to  protect  the  proteins  from  bacterial  decom- 
position. 

In  the  second  place,  an  abundant  supply  of  soluble  nitrogenous 
matter  stimulates  the  multiplication  and  activity  of  the  or- 
ganisms and  so  brings  about  a  more  extensive  fermentation  of 
the  carbohydrates  of  the  feed,  as  is  evidenced  by  an  increase 
in  the  methane  given  off  and  in  the  proportion  of  the  carbo- 
hydrates apparently  digested. 

Third,  it  seems  to  be  fairly  well  made  out  that  the  nitrogen 
which  these  organisms  assimilate  is  utilized  to  build  up  their 
protoplasm  and  thus,  by  a  sort  of  symbiosis,  becomes  a  source 
of  protein  to  their  host.  It  has  been  claimed  that  this  bacterial 
protein  is  indigestible,  but  the  evidence  on  which  this  claim 
is  based  is  capable  of  a  different  interpretation  and  there  seems 
to  be  good  reason  for  believing  that  it  may  be  acted  on  in  the 
stomach  and  intestines  by  the  digestive  enzyms  like  other  pro- 
teins and  serve  as  a  source  of  protein  to  the  body.  Some  of 
the  evidence  in  favor  of  this  view  is  presented  in  a  subsequent 
discussion  of  the  nutritive  value  of  the  non-proteins  (786-789). 


DIGESTION  AND   RESORPTJON^  '  IOI 


The  digestion  of  ash 


The  various  digestive  enzyms  whose  action  has  been  con- 
sidered in  the  foregoing  pages  bring  about  extensive  chemical 
changes  in  the  organic  nutrients  of  feeding  stuffs  by  means  of 
which  they  are  prepared  to  enter  into  the  nutritive  processes 
in  the  tissues.  At  the  same  time,  the  so-called  "  inorganic  " 
ingredients  of  feed  are  also  prepared  for  resorption,  but  the  di- 
gestion of  these  substances  has  been  less  extensively  studied 
than  that  of  the  organic  nutrients. 

142.  Sulphur  and  phosphorus.  —  As  regards  the  sulphur  of 
the  proteins,  it  does  not  appear  that  this  element  is  separated 
from  its  union  with  carbon,  nitrogen  and  hydrogen  in  the  pro- 
cesses of  protein  digestion.     The  sulphur  of  the  proteins  is  con- 
tained in  the  amino-acid  cystin,  which,  so  far  as  known,  is 
resorbed  without  further  change.     As  regards  the  phosphorus  of 
the  nucleo-proteins,  opinions  still  differ  as  to  whether  it  is  split 
off  as  phosphoric  acid  in  the  course  of  digestion  or  resorbed,  still 
in  "organic"  combination,  as  a  nucleosid.     To  what   extent 
other  ash  ingredients  are  taken  up,  like  sulphur  and  phosphorus, 
in  organic  combination,  it  is  difficult  to  say,  but  that  such  re- 
sorption takes  place  is  to  be  regarded  as  probable. 

143.  Electrolytes.  —  As    regards    those    ash    ingredients    of 
feeds  which  are  present  as  electrolytes,  it  may  be  assumed  that 
they  are  brought  into  solution  to  a  greater  or  less  extent  by  the 
hydrochloric  acid  of  the  gastric  juice,  but  how  much  reprecipi- 
tation  may  occur  in  the  more  or  less  alkaline  contents  of  the 
intestine  it  is  difficult  to  say.     The  whole  subject  of  the  diges- 
tion, of  the  ash  ingredients  of  feeding  stuffs,  however,  is  so  in- 
timately related  to  the  question  of  the  paths  of  excretion  and  to 
the  problems  of  ash  metabolism  that  it  can  be  more  profitably 
considered  in  that  connection. 

Summary  of  changes  in  digestion 

144.  Solution  of  nutrients.  —  The  substances  which  make 
up  the  larger  part  of  the  feed  of  domestic  animals  (and  of  man 
as  well)  are  comparatively  insoluble  in  water.     Some  of  them, 
such  as  cellulose  and  the  fats,  may  be  regarded  as  practically 
entirely  insoluble.     Others,  like  starch  and  the  proteins,  are 


102  i^TiTLDN  OF   FARM   ANIMALS 


sparingly  s-X  :  While  small  amounts  of  soluble  proteins 
and  somewhat  larger  quantities  of  soluble  carbohydrates  occur, 
they  ordinarily  play  but  a  subordinate  role  in  nutrition.  One 
obvious  result  of  the  chemical  changes  brought  about  by  the 
enzyms  and  organized  ferments  of  the  digestive  tract  is  to 
convert  these  insoluble  substances  into  soluble  ones.  Thus 
starch  yields  sugar,  cellulose  the  organic  acids,  fats  form 
soaps  and  protein  yields  peptones  and  amino  acids.  It  was 
natural,  therefore,  that  digestion  should  be  looked  upon  as 
a  process  of  solution  and  compared  to  the  preparation  of 
extracts  in  a  pharmaceutical  laboratory  by  means  of  various 
solvents. 

The  solvent  action  of  the  digestive  juices  is  important,  since 
the  animal,  like  the  plant,  absorbs  its  real  food  substances 
substantially  in  aqueous  solution.  The  mere  dissolving  of  the 
ingredients  of  the  feeds,  however,  is  far  from  being  the  only  or 
even  the  chief  function  of  the  digestive  juices,  as  is  clearly 
indicated,  for  example,  by  the  existence  of  a  coagulating  enzym 
like  chymosin,  which  precipitates  the  soluble  casein,  or  the  pres- 
ence of  the  various  invertases,  which  attack  substances  already 
soluble. 

145.  Colloids  converted  into  crystalloids.  —  The  principal 
nutrients  belong  to  the  class  of  substances  called  colloids. 
Gelatin  is  a  typical  colloid  as  are,  indeed,  all  the  proteins  and 
the  more  abundant  carbohydrates,  while  the  sugars,  organic 
acids,  etc.,  are  classed  as  crystalloids. 

As  related  to  digestion,  the  most  important  distinction  be- 
tween colloids  and  crystalloids  is  the  difference  in  the  osmotic 
pressures  of  their  solutions  by  virtue  of  which  crystalloids 
diffuse  readily  through  permeable  membranes.  This  diffusi- 
bility  plays  an  important  part  in  the  resorption  of  the  digested 
material  into  the  blood  and  lymph  current,  as  will  appear  in  the 
next  section,  although  it  is  by  no  means  the  only  factor  con- 
cerned. 

A  review  of  the  chemical  changes  which  take  place  in  diges- 
tion shows  that  they  are  all  in  the  direction  of  molecular  simplifi- 
cation. They  are  substantially  processes  of  cleavage  by  which 
large  molecules  are  split  into  two  or  more  smaller  ones.  Such 
a  change,  however,  is  in  the  direction  from  the  colloid  to  the 
crystalloid  condition.  The  final  products  of  digestion  are 


DIGESTION  AND   RESORPTION  103 

mostly  substances  of  comparatively  low  molecular  weight, 
readily  soluble  in  water  and  having  a  relatively  high  osmotic 
pressure  and  therefore  readily  diffusible.  This  difference  is 
most  marked  in  some  of  the  more  simple  cleavage  products  of 
the  proteins  and  least  so  in  the  case  of  the  digestive  products 
of  the  fats. 

146.  Uniformity  in  nutritive  material.  —  The  feed  consumed, 
especially  by  herbivora,  is  of  a  very  heterogeneous  character. 
The  proteins  and  carbohydrates  in  particular  are  present  in 
great  variety,  so  that  the  nature  and  proportions  of  the  sub- 
stances out  of  which  the  body  must  draw  the  material  for  the 
construction  and  maintenance  of  its  tissues  may  vary  greatly 
at  different  times.     Under  the  action  of  the  digestive  enzyms, 
however,  these  diverse  substances  all  yield  substantially  the 
same  products  so  that  the  nutritive  solution  supplied  to  the  body 
proper  is  qualitatively  of  a  very  uniform  composition,  contain- 
ing chiefly  monosaccharids,  various  acids  of  the  aliphatic  series, 
amino  acids  derived  from  the  proteins,  and  the  soluble  ash  in- 
gredients.    By  this  preliminary  action  upon  the   feed   in   the 
digestive  canal,  —  i.e.,   practically   outside    the    body,  —  the 
organism  is  rendered  independent  of  the  particular  kinds  of  feed 
available,   its   cells   being   constantly   supplied   with   uniform 
nutritive  material. 

147.  Molecular   simplification.  —  It  has  just  been  pointed 
out  (145)  that  digestion  from  the  chemical  standpoint  consists 
substantially  of  a  series  of  hydrolytic  cleavages  of  the  nutrients, 
yielding  compounds  of  lower  molecular  weight  and  greater  solu- 
bility   and    diffusibility.     This    molecular    simplification    has, 
however,  a  more  important  aspect  which  is  most  strikingly 
illustrated  in  the  case  of  the  proteins.     It  was  shown  in  Chap- 
ter I  that  the  proteins,  although  very  similar  in  many  physical 
properties,  may  differ  widely  from  each  other  as  regards  molecu- 
lar structure.     This  is  shown  in  the  first  place  by  the  wide 
variations  in  the  proportions  of  the  constituent  amino  acids 
which  they  yield    on    hydrolysis  (50).     Moreover,  even  were 
these  cleavage  products  present  in  the  same  proportions,  the 
existence  of  optical  isomers  and  the  possible  variations  in  the 
order  and  manner  of  linkage  of  the  amino  acids  afford  almost 
endless  possibilities  of  isomerism.     Studies  in  immunity  have 
in  fact  revealed  striking  specific  differences  between  proteins 


104  NUTRITION  OF  FARM  ANIMALS 

bearing  the  same  name  but  derived  from  different  species  or 
different  individuals  of  the  same  species,  the  proteins  of  one 
animal  often  being  toxic  to  another. 

The  body  proteins,  then,  are  specific  both  as  to  composition 
and  structure  and  differ  in  both  respects  from  those  of  the  feed. 
In  order  that  the  latter  may  nourish  the  organism  they  must  be 
converted  into  the  specific  proteins  of  the  body.  This  is  accom- 
plished through  their  cleavage  in  the  digestive  tract  into  their 
constituent  "  building  stones "  which  the  body  may  then 
reassemble  to  form  proteins  constructed  according  to  its  own 
specific  pattern.  Not  only  so,  but  the  proteins  of  different 
tissues  or  even  cells  must  be  regarded  as  specific.  The  body 
proteins  are  built  not  after  a  single  pattern  but  after  numerous 
ones.  It  is  only  by  a  very  extensive,  even  if  not  complete 
(139),  breaking  down  of  the  structure  of  the  feed  proteins  that 
it  becomes  possible  for  the  body  to  build  up  out  of  the  fragments 
the  various  proteins  which  it  requires.  "Its  protein  mole- 
cules have  a  different  architecture  from  those  of  the  plant." 
This  fact  throws  an  interesting  light  upon  the  coagulation  of 
the  soluble  casein  of  milk  in  the  stomach.  Although  present 
in  soluble  form,  it  is  not  a  body  protein  and  its  coagulation 
serves  to  retain  it  in  the  digestive  tract  and  give  the  proteolytic 
enzyms  an  opportunity  to  break  it  up  into  its  constituent 
amino  acids. 

What  is  so  strikingly  true  of  the  proteins  is  likewise  true  of 
other  nutrients.  The  digestive  cleavages  serve  not  merely, 
or  perhaps  not  chiefly,  to  render  them  soluble  and  diffusible 
but  to  reduce  the  molecular  complexes  to  forms  which  the  body 
cells  can  assimilate.  The  carbohydrates,  e.g.,  are  converted 
into  monosaccharids,  even  the  somewhat  larger  molecules  of 
the  disaccharids  appearing  to  be  too  large  or  to  have  an  un- 
suitable molecular  structure  for  the  body  cells  to  use.  In 
general  the  complex  compounds  of  the  feed  are  split  up  by  the 
enzyms  of  the  digestive  fluids  into  their  constituent  atomic 
groupings  or  "  building  stones  "  which  supply  the  material  out 
of  which  the  body  by  selection  and  rearrangement  builds  up 
the  proteins,  carbohydrates  and  fats  peculiar  to  itself,  and  the 
value  of  a  feed  depends  upon  the  nature  and  amounts  of  the 
cleavage  products  which  it  yields  in  digestion  rather  than  upon 
the  specific  substances  which  it  contains. 


DIGESTION  AND   RESORPTION 


105 


§  3.   RESORPTION  —  THE  FECES 

148.  Definition.  —  As  was 'stated  at  the  beginning  of  this 
chapter  (113),  the  digested  feed  contained  in  the  alimentary 
canal  is  really  outside  the  body,  just  as  in  the  case  of  the  ameba. 
In  order  to  enter  the  body,  the  digested  material  must  pass 
through  or  be  taken  up  by  the  cells  surrounding  the  digestive 
cavity.     The  process  by  which  the  products  of  the  digestion  of 
the  feed  are  transferred  from  the  digestive  organs  to  the  circulat- 
ing media  (blood  and  lymph)  of  the  body  is  called  resorption. 

149.  Epithelium.     Villi.  —  The  inner,  or  mucous,  membrane 
of  the  digestive  tract  bears  on  its    surface   a   layer   of   epi- 


FIG.  14.  —  Section  of  villi.     (Bohm,  Davidorf,  Huber,  Text  Book  of  Histology.) 

thelial  cells,  more  or  less  resembling  those  lining  the  mouth,  which 
is  closely  underlaid  with  a  network  of  blood  capillaries  and 
lymph  vessels.  It  is  these  epithelial  cells  which  are  the  active 
agents  in  resorption. 


106  NUTRITION  OF  FARM  ANIMALS 

In  the  higher  animals  the  extent  of  resorbing  surface  is  greatly 
increased  by  certain  projections  of  the  interior  surface  of  the 
small  intestine  known  as  the  mill.  Those  are  round  or  club- 
shaped  protuberances  of  the  inner  surface  of  the  intestine. 
They  are  covered,  like  all  parts  of  the  intestinal  surface,  with  the 
epithelial  cells  just  described,  which  are  underlaid  by  a  deli- 
cate membrane,  beneath  which  are  found  numerous  minute 
capillary  blood-vessels,  a  layer  of  smooth  (involuntary)  mus- 
cular fibers  and  a  network  of  nerves.  In  the  center  of  each 
villus  ends  a  vessel  called  a  lacteal,  belonging  to  the  lymphatic 
system.  Figure  14  shows  a  longitudinal  section  of  three  villi. 

The  villi  are  absent  in  the  stomach  and  in  the  large  intestine. 
Although  some  resorption  takes  place  in  the  stomach,  and  while 
a  considerable  amount  of  water  and  more  or  less  of  the  fermen- 
tation products  are  resorbed  in  the  large  intestine,  the  small 
intestine  is  the  special  resorptive  organ. 

150.  Mechanism  of  resorption.  —  Since  the  processes  of 
digestion  are  apparently  directed  toward  the  conversion  of  feed 
substances  into  soluble  and  diffusible  forms,  it  was  quite  natural 
that  resorption  should  be  regarded  as  an  osmotic  process.  In 
this  conception  of  it,  the  epithelial  cells  and  other  tissues  be- 
tween the  cavity  of  the  digestive  organs  and  the  blood  and  lymph 
vessels  constituted  a  membrane  through  which  osmosis  took 
place.  On  the  one  side  of  this  membrane  were  the  contents 
of  the  digestive  tract,  containing  the  soluble  products  of,  diges- 
tion, while  on  the  other  side  were  the  blood  and  lymph,  contain- 
ing little  or  none  of  these  products.  Under  these  conditions, 
osmosis  was  assumed  to  set  in  and  transfer  the  digested  nutrients 
to  the  blood  and  lymph. 

Undoubtedly  osmosis  plays  an  important  part  in  resorption, 
but  its  effects  are  profoundly  modified  by  the  properties  of  the 
resorbing  cells  of  the  intestinal  epithelium  in  ways  which  as  yet 
are  but  very  partially  understood,  and  resorption  can  by  no 
means  be  explained  by  a  simple  analogy  with  the  parchment 
dialyzing  -tube  of  the  laboratory. 

Differences  in  the  permeability  of  the  epithelial  cells  and  of  the 
intercellular  substance  for  the  various  dissolved  substances  in  the 
digestive  tract  doubtless  play  their  part  in  bringing  about  the  phe- 
nomena of  selective  resorption,  while  variations  in  the  affinity  of  the 
cell  colloids  for  water  may  be  assumed  to  influence  the  resorp- 


DIGESTION  AND   RESORPTION  107 

tion  of  that  substance  as  well  as  of  salts.  There  are  other  facts, 
however,  for  which  it  is  difficult  at  present  to  offer  any  physico- 
chemical  explanation.  Notable  among  these  is  the  predominant  per- 
meability of  the  intestinal  epithelium  in  one  direction,  viz.,  from  the 
intestinal  lumen  towards  the  blood  and  lymph  vessels. 

For  the  present,  it  is  necessary  to  be  content  with  the  state- 
ment that  resorption  is  a  function  of  the  living  epithelial  cells, 
although  such  a  statement,  of  course,  explains  nothing  but 
simply  means  that  it  is  impossible  at  present  to  form  an  adequate 
conception  of  the  intimate  mechanism  of  the  process. 

Resorption  might  be  characterized  briefly  as  a  reverse  se- 
cretion. In  secretion  the  active  cells  of  a  gland  take  materials 
from  the  blood  or  lymph,  transform  them  into  the  specific 
substances  characteristic  of  the  cells,  and  then  eject  the  latter 
into  the  duct  of  the  gland.  The  epithelial  cells  of  the  digestive 
tract,  on  the  other  hand,  take  up  digested  materials  from  the 
contents  of  the  alimentary  canal,  modify  them  more  or  less 
chemically  and  transmit  the  products  to  the  blood  or  lymph. 

151.  Paths  of  resorption.  —  Most  of  the  resorbed  substances 
seem  to  pass  from  the  epithelial  cells  to  the  blood  in  the  capil- 
laries and  thus  finally  through  the  portal  vein  (182)  to  the  liver. 
This  is  true  of  the  cleavage  products  of  the  proteins,  of  carbo- 
hydrates, organic  acids,  salts  and  water.     Fats,  on  the  other 
hand,  enter  the  circulation  chiefly  or  wholly  through  the  lymph 
in  the  form  of  minute  droplets  which  are  secreted  by  the  epi- 
thelium into  the  lacteals  of  the  villi,  whence  they  pass  through 
the  lymphatics  to  the  thoracic  duct  (186). 

152.  Chemical    changes    in    resorption.  —  It    is    somewhat 
generally  believed  that  the  products  of  digestion,  especially  of 
the  proteins  and  fats,  undergo  rather  extensive  chemical  changes 
in  the  epithelial  cells  during  the  process  of  resorption.     This 
question  is  considered  more  particularly  in  Chapter  V  but  may 
be  briefly  referred  to  here  for  the  sake  of  completeness. 

Proteins.  —  In  digestion  the  proteins  yield  comparatively 
simple  cleavage  products.  It  has  been  maintained,  especially 
by  Abderhalden  and  his  school,  that  these  cleavage  products 
are  resynthesized  in  the  epithelial  cells  into  serum  albumin, 
which  is  regarded  as  the  common  source  of  all  the  body  proteins. 
This  view  has  been  based  chiefly  on  the  failure  to  detect  amino 
acids  or  other  protein  cleavage  products  in  the  blood  coming 


I08  NUTRITION  OF  FARM  ANIMALS 

from  the  intestines  even  during  the  height  of  protein  resorption. 
Folin  and  Denis  and  also  Van  Slyke  and  Meyer  have  recently 
demonstrated,  however,  that  sufficiently  delicate  tests  show 
the  presence  of  such  products  in  the  portal  blood  in  amounts 
as  large  as  could  be  expected  in  view  of  the  gradual  nature  of 
digestion  and  resorption  and  of  the  large  volume  of  blood  pass- 
ing through  the  intestinal  capillaries.  The  prevailing  opinion 
seems  to  be  at  present  that  the  digestive  products  of  the  pro- 
teins undergo  relatively  little  modification  before  entering  into 
the  circulation. 

Fats.  —  The  mechanism  of  fat  resorption  has  been  the  subject 
of  heated  controversy.  Some  physiologists  have  maintained 
that  it  is  chiefly  a  physical  process ;  that  globules  of  emulsified 
feed  fat  are  taken  up  bodily  by  the  epithelial  cells  and  excreted 
again  by  them  into  the  lacteals.  This  view  is  based  largely 
on  microscopical  observations  which  show  the  presence  of  ap- 
parently unaltered  fat  globules  of  the  intestinal  emulsion  in 
the  protoplasm  of  the  epithelial  cells  and  in  the  lymph  of  the 
lacteals  after  the  ingestion  of  fat.  Other  no  less  eminent  physi- 
ologists, however,  have  as  stoutly  held  that  fats  are  not  resorbed 
unaltered  but  only  after  cleavage  into  glycerol  and  fatty  acids 
(or  their  salts),  which  are  soluble  in  bile  (135),  and  that  the  fat 
globules  observed  in  the  epithelial  cells  are  the  product  of  a 
resynthesis.  At  present  the  weight  of  scientific  opinion  is 
strongly  in  favor  of  this  latter  view.  It  is  perhaps  true  that 
unaltered  fat  droplets  may  be  taken  up  by  the  epithelial  cells 
but  that  any  considerable  amount  of  fat  is  resorbed  in  this 
fashion  is  to  say  the  least  very  questionable. 

At  any  rate,  the  digested  fat  reaches  the  lacteals  almost  en- 
tirely in  the  form  of  fat,  so  that  after  a  meal  containing  much 
fat  the  lacteals  are  filled  with  a  milky  fluid  and  the  lymph  is 
found  to  contain  relatively  large  amounts  of  neutral  fats.  It 
is  clear,  then,  that  the  resorbed  soaps  and  fatty  acids  are  speedily 
synthesized  to  fat  again.  This  synthetic  power  is  still  further 
and  strikingly  demonstrated  by  the  fact  that  free  fatty  acids 
are  readily  digested  but  are  transmitted  to  the  lacteals  in  the 
form  of  the  corresponding  neutral  fats,  having  evidently  been 
combined  with  glycerol  in  the  process  of  resorption,  although 
the  source  from  which  the  body  derives  its  glycerol  is  still  un- 
certain. Evidently,  then,  from  this  point  of  view,  nothing 


DIGESTION  AND   RESORPTION  1 09 

stands  in  the  way  of  the  supposition  that  the  digested  fats  are 
completely  split  up  into  glycerol  and  fatty  acids  in  the  process 
of  digestion  and  synthesized  again  in  the  epithelial  cells,  although, 
on  the  other  hand,  of  course,  it  does  not  prove  that  such  is  the 
case. 

153.  The  feces.  —  As  the  contents  of  the  digestive  tract  move 
forward  through  the  small  and  large  intestines  they  become 
progressively  more  and  more  impoverished  in  digestible  material 
and  also,  in  the  lower  portion  of  the  large  intestine,  are  deprived 
of  part  of  their  water,  so  that  there  accumulates  in  the  rectum 
a  more  or  less  solid  residue  which  is  voided  at  intervals  as  the 
feces. 

The  feces  are  to  be  regarded  as  both  an  excretory  product 
(198)  and  a  feed  residue. 

154.  The  feces  as  an  excretory  product.  —  The  fact  that  the 
feces  are  an  excretory  product  is  most  obvious  in  the  carnivora, 
whose  normal  feed  consists  of  substances  almost  wholly  diges- 
tible, but  it  is  evident  also  in  man.     On  a  pure  meat  diet,  for 
example,  feces  continue  to  be  produced  in  which  undigested 
feed  residues  are  either  absent  entirely  or  present  in  minimal 
amounts  only.     Even  a  fasting  animal  continues  to  produce 
feces,  while  an  empty  loop  of  the  intestine,  separated  from  the 
remainder  of  the  digestive  tract,  soon  fills  up  with  fecal-like 
material. 

The  excretory  ingredients  of  the  feces  include  unresorbed 
digestive  juices  and  their  decomposition  products,  intestinal 
mucus,  worn-out  epithelial  cells  and  cell  fragments,  leucocytes 
and  excretions  of  the  intestinal  mucosa.  Especially  notable 
among  the  latter  are  salts  of  calcium  and  of  iron  and  in  herbivora 
the  phosphates  of  calcium  and  magnesium.  The  feces  also 
include  a  not  inconsiderable  proportion  of  intestinal  micro- 
organisms. 

155.  The  feces  as  a  feed  residue.  —  The  ordinary  mixed 
diet  of  man,  and  to  a  much  more  marked  degree  the  ordinary 
feed  of  herbivorous  animals,  contains  relatively  considerable 
amounts  of  materials  which  are  either  indigestible  or  which  for 
one  reason  or  another  escape  digestion  and  therefore  reappear 
in  the  feces.     Among  these,  some,  like  lignin,  cutin,  the  waxes, 
chlorophyl   and    other   non-fatty   ingredients    of    the   "  ether 
extract,"  and  the  insoluble  ash  ingredients,  may  be  regarded 


110  NUTRITION  OF  FARM  ANIMALS 

as  wholly  indigestible.  Of  more  importance,  however,  are 
such  carbohydrates  as  cellulose  and  the  various  hemicelluloses, 
the  levulans,  galactans,  mannans,  pentosans,  etc.,  which 
may  be  said  to  be  practically  only  partially  digestible. 
By  this  is  not  meant,  of  course,  that  one  molecule  of  cellulose, 
e.g.,  is  any  less  digestible  per  se  than  another,  but  only  that 
part  of  the  cellulose  of  ordinary  feeds  does  as  a  matter  of  fact 
escape  digestion,  largely  because  the  length  of  time  during 
which  it  is  exposed  to  the  action  of  the  organisms  which  attack 
it  is  insufficient  to  allow  of  its  complete  solution.  The  feces  of 
herbivorous  animals,  therefore,  contain  amounts  of  these  di- 
verse carbohydrates  varying  with  the  character  of  the  feed  and 
the  activity  of  the  fermentation  processes  in  the  digestive  tract. 
Since  these  compounds  are  especially  abundant  in  the  roughages, 
the  feces  from  these  feeds  are  bulky  and  especially  rich  in  un- 
digested "  crude  fiber." 

Other  ingredients,  particularly  of  vegetable  feeding  stuffs, 
partially  escape  digestion  not  on  account  of  any  lack  of  the  ap- 
propriate digestive  enzyms  but  because  they  are  mechanically 
protected  from  the  action  of  the  latter.  If  granules  of  starch, 
e.g.,  are  contained  within  a  cell  which  has  not  been  ruptured 
during  the  mastication  of  the  feed,  the  cell  wall  tends  to  protect 
them  from  the  action  of  the  digestive  juices,  and  they  may  escape 
digestion  although  per  se  entirely  digestible.  The  extent  to 
which  such  a  nutrient  will  actually  be  digested,  therefore,  will 
depend  to  a  considerable  degree  upon  whether  the  cellulose  of 
the  cell  wall  is  attacked  and  destroyed  by  the  organisms  of  the 
alimentary  canal.  What  is  true  of  starch  in  this  respect  is 
obviously  true  of  all  cell  enclosures,  and  explains  why  more  or 
less  matter  intrinsically  digestible  may  be  rejected  in  the  feces. 
For  a  like  reason,  seeds  which  escape  mastication  are  but  im- 
perfectly digested,  being  protected  by  the  relatively  insoluble 
seed  coats.  Similarly,  cellulose  itself  may  be  so  impregnated 
with  lignin  and  cutin  substances  that  the  "  crude  fiber  "  may 
be  attacked  only  with  difficulty  or  not  at  all  by  the  methane 
fermentation. 

Finally,  there  is  to  be  considered  the  possibility  of  a  mis- 
proportion  between  digestion  and  resorption.  In  heavy  rations, 
especially,  substances  which  are  actually  digested  may  per- 
haps escape  resorption  through  insufficient  contact  with  the 


DIGESTION  AND   RESORPTION  III 

intestinal  walls  or  from  lack  of  time,  and  so  be  found  in  the 
feces. 

156.  Composition  of  feces.  —  Evidently  the  feces  are  a  very 
complex  and  variable  mixture,  including,  on  the  one  hand,  the 
various  excretory  products  just  enumerated  and,  on  the  other 
hand,    indigestible   feed   substances  'and   digestible   materials 
which  have  for  one  reason  or  another  escaped  actual  digestion 
or   which,   having   been   digested,   have  failed   of   resorption. 
Among  the  latter  may  be  included  unresorbed  products  of  the 
putrefaction  of  the  proteins,  especially  skatol,  which  impart 
to  the  feces  their  offensive  odor. 

The  proportions  of  these  two  groups  —  the  excretory  products 
and  the  feed  residues  —  in  the  feces  vary  widely  with  the 
nature  of  the  feed  consumed.  In  the  carnivora  the  body  wastes 
predominate,  so  that  the  feces  of  these  animals  are  to  be  regarded 
as  primarily  an  excretory  product.  To  a  considerable  degree 
the  same  thing  is  true  of  man,  especially  when  living  on  a  con- 
centrated diet.  With  the  herbivora,  on  the  contrary,  the  in- 
digestible or  undigested  feed  residues  constitute  the  bulk  of 
the  feces,  although  the  amount  of  true  excretory  products  is 
by  no  means  insignificant.  Omnivora  like  the  hog  occupy  an 
intermediate  position  in  this  respect. 

§  4.    THE  DETERMINATION  or  DIGESTIBILITY 

157.  Definition  of  digestibility.  —  The  words  digestible  and 
digestibility  are  used  in  more  than  one  sense.     Sometimes,  for 
example,  a  food  is  said  to  be  digestible  because  it  is  easily  di- 
gested —  that  is,  causes  no  unpleasant  sensation  after  it  is 
eaten  —  while  by  an  indigestible  food  is  meant  one  that  is  apt 
to  cause  gastric  or  intestinal  disturbances.     Again,  it  is  not  un- 
common to  judge  of  the  digestibility  of  stock  feeds  by  their 
effects  and  to  regard  that  one  as  the  more  digestible  which  causes 
or  seems  to  cause  the  greater  gain  in  weight. 

The  word  digestibility  as  used  in  the  study  of  animal  nutrition, 
however,  has  a  definite  and  limited  meaning.  It  denotes  the 
percentage  of  the  feed,  or  of  any  single  ingredient  of  the  feed, 
which  is  dissolved  or  otherwise  acted  on  in  the  digestive  canal 
so  that  it  can  be  resorbed  and  thus  put  at  the  disposal  of  the 
body  cells.  For  example,  the  digestion  experiment  with  a  steer 


112  NUTRITION  OF  FARM  ANIMALS 

described  in  a  subsequent  paragraph  (160)  showed  that  out  of 
each  100  grams  of  protein  in  the  clover  hay  eaten  by  the  animal 
53  grams  were  apparently  digested  and  resorbed.  The  digesti- 
bility of  the  protein  in  this  case,  therefore,  is  said  to  be  53  per 
cent.  Digestibility  in  this  sense  is  obviously  a  conception 
entirely  distinct  from  that  of  rapidity  or  ease  of  digestion.  A 
feed  may  have  no  injurious  nor  disagreeable  effects  and  yet 
may  have  a  low  percentage  digestibility  —  straw,  for  example. 

Neither  does  the  percentage  digestibility  alone  determine 
the  effect  produced  by  a  feed.  Two  feeds  may  be  equally  di- 
gestible and  yet  one  may  be  more  valuable  than  the  other  be- 
cause its  digested  matter  can  be  used  to  better  advantage  by 
the  body.  Nevertheless,  it  is  clear  that  the  indigestible 
portion  of  the  feed  can  make  no  contribution  to  the  nutrition 
of  the  body.  The  first  step,  therefore,  although  by  no  means 
the  last  one,  in  comparing  the  values  of  different  feeds  or  rations 
is  to  determine  as  accurately  as  possible  what  proportion  of 
each  ingredient  is  capable  of  digestion.  In  other  words,  we 
shall  seek  to  add  to  the  qualitative  knowledge  of  the  processes 
of  digestion  and  resorption  outlined  in  the  preceding  sections 
a  quantitative  knowledge  of  the  extent  of  digestion. 

158.  Method  of  digestion  experiments.  —  The  percentage 
digestibility  of  feeding  stuffs  can,  as  a  rule,  be  determined  only 
by  trial  with  an  animal.  Such  trials  are  called  digestion  ex- 
periments, and  a  brief  outline  of  the  way  in  which  they  are  made 
will  aid  in  understanding  just  what  is  meant  by  digestibility. 

The  method  is  substantially  that  originated  by  Henneberg 
and  Stohmann  in  their  early  investigations  (707).  Since  it  is 
obviously  impossible  to  collect  and  measure  the  substances 
digested  and  resorbed  from  the  feed,  it  is  necessary  to  have 
recourse  to  an  indirect  method,  viz.,  to  determine  what  portions 
of  the  feed  are  not  digested  and  compute  by  difference  the 
amounts  digested.  As  already  stated  (155),  the  undigested 
portions  of  the  feed  are  excreted  in  the  feces.  A  digestion 
experiment  really  consists  in  determining  as  exactly  as  may  be 
how  much  of  the  feed  is  thus  rejected,  any  portions  of  it  which 
disappear  during  its  passage  through  the  alimentary  canal  being 
regarded  as  digested. 

If  the  feces  consisted  only  of  undigested  feed  residues,  the 
matter  would  be  very  simple,  but  they  also  include  a  greater  or 


DIGESTION  AND   RESORPTION 


less  proportion  of  excretory  products  (154).  In  the  case 
herbiyora,  the  proportion  of  the  latter  is  relatively  small  and 
in  the  digestion  experiment  as  ordinarily  conducted  is  neglected, 
it  being  assumed,  in  other  words,  that  the  feces  are  equivalent 
to  undigested  feed  residues.  The  same  method  is  pursued  in 
digestion  experiments  with  swine,  although  in  these  animals  £-- 
the  proportion  of  excretory  products  in  the  feces  is  larger.  The 
error  thus  introduced  into  digestion  experiments  is  not  negligible, 
especially  as  regards  certain  ingredients.  It  will  be  convenient, 
however,  to  take  up  first  the  methods  of  digestion  experiments 
as  ordinarily  conducted  and  to  consider  later  the  nature  and 
extent  of  the  errors  introduced  by  neglecting  the  presence  of  the 
excretory  products. 

159.   Time  required  for  digestion  experiments.  —  It  is  es- 
sential that  a  digestion  experiment  be  preceded  by  a  prelimi- 


FIG.  15.  —  Steer  in  digestion  stall.     (Bailey's  Cyclopedia  of  American  Agriculture.) 

nary  period  in  which  the  feed  to  be  investigated  is  fed  in  the  same 
weighed  amounts  daily  as  in  the  actual  experiment.  This  is 
for  the  purpose  of  removing  from  the  digestive  tract  residues 


114  NUTRITION  OF  FARM  ANIMALS 

of  previous  feeds  and  also  of  establishing  as  uniform  a  rate  of 
excretion  of  feces  as  practicable.  In  the  case  of  ruminants,  such 
a  preliminary  period  should  extend  over  one  or  two  weeks,  while 
with  swine  it  may  be  made  somewhat  less.  In  the  succeeding 
digestion  experiment  proper,  the  same  feeding  is  continued 
and  the  feces  are  collected  quantitatively  for  a  number  of  days 
(seven  to  ten  or  more),  in  order  to  eliminate  the  error  due  to  the 
irregularity  of  the  excretion  from  day  to  day.  From  the 
weights  of  feeds  and  feces  and  their  composition  as  determined 
by  analysis,  the  digestibility  is  computed  as  illustrated  in  the 
following  paragraphs. 

160.  Example  of  a  digestion  experiment.  —  A  steer  was  fed  3.7 
kilograms  of  clover  hay  per  day  for  three  weeks.  During  the  last 
ten  days  of  this  time,  the  average  weight  of  the  daily  feces  was  5.662 
kilograms.  Samples  of  each  were  analyzed  and  found  to  contain 
the  following  percentages  of  dry  matter. 

Clover  hay 84.97  Per  cent 

Feces 22. 36  per  cent 

The  3.7  kilograms  of  hay,  therefore,  contained  3.144  kilograms  of 
dry  matter  while  the  5.662  kilograms  of  feces  excreted  contained 
only  1.267  kilograms  of  dry  matter.  The  difference,  1.877  kilograms, 
which  did  not  appear  in  the  feces,  is  regarded  as  having  been  digested 
by  the  steer.  This  amount  is  59.7  per  cent  of  the  3.144  kilograms 
eaten;  we  say,  then,  that  the  percentage  digestibility  of  the  dry 
matter  of  this  hay  was  59.7  and  this  number  is  sometimes  called  its 
"digestion  coefficient." 

In  precisely  the  same  way  the  percentage  digestibility  of  each  in- 
gredient may  be  computed  from  the  results  of  analyses  of  the  hay 
and  of  the  feces,  which  in  this  case  gave  the  following  results :  — 

HAY  FECES 

%  % 

Water 15.03  77.64 

Ash 5.49  1.92 

Protein 10.24  3.13  l 

Non-protein 1.36 

Crude  fiber 28.61  9.29 

Nitrogen-free  extract 36.98  7.50 

Ether  extract 2.29  0.52 

100.00  100.00 

1  All  the  nitrogen  of  the  feces  is  here  assumed  to  exist  in  the  form  of  protein,  an 
assumption  which,  as  will  appear  later,  is  far  from  being  true  (166),  but  which 
does  not  affect  the  method  of  computation. 


DIGESTION  AND   RESORPTION 


These  figures,  together  with  the  weights  of  hay  eaten  and  feces 
excreted  per  day,  yield  the  following  results :  — 

TABLE  20.  —  RESULTS  OF  A  DIGESTION   EXPERIMENT 


NITRO- 

DRY 

MATTER 

ASH 

PRO- 
TEIN 

NON- 
PROTEIN 

CRUDE 
FIBER 

GEN 
FREE 
I  EX- 

ETHER 
EX- 
TRACT 

TRACT 

Kgs. 

Kgs. 

Kgs. 

Kgs. 

Kgs. 

Kgs. 

Kgs. 

In  hay  eaten    .     .     . 

3-J44 

0.203 

0-379 

0.050 

1.059 

1.368 

0.085 

In  feces  excreted  .     . 

1.267 

0.109 

0.177 

— 

0.526 

0.425 

0.030 

Difference  =  digested 

1.877 

0.094 

O.2O2 

0.050 

0-533 

0.943 

0-055 

Percentage      digesti- 

bility   

CTQ.7O 

4.6.4.8 

c?  19 

IOO.OO 

50.27 

68  04. 

65.02 

161.  Digestibility  of  concentrates.  —  The  method  just  outlined 
for  determining  the  digestibility  of  a  roughage  or  of  a  total  ration 
is  in  conception  very  simple.  The  determination  of  the  digestibility 
of  concentrates  by  herbivora  is  somewhat  more  complicated,  since 
they  cannot  be  made  the  sole  feed  of  these  animals.  They  must, 
therefore,  be  fed  along  with  a  known  amount  of  a  roughage  whose 
digestibility  by  the  same  animal  is  likewise  determined  in  a  preced- 
ing or  following  period.  From  the  digestibility  of  the  total  ration 
and  the  known  digestibility  of  the  roughage  that  of  the  concentrate 
is  obtained  by  means  of  a  second  calculation  by  difference. 

Thus,  the  same  steer  used  in  the  experiment  of  the  preceding  para- 
graph received  per  day  in  a  subsequent  period  the  same  amount,  3.7 
kilograms,  of  clover  hay  and  in  addition  4  kilograms  of  maize  meal. 
The  average  daily  excretion  of  feces  on  this  mixed  ration  was  8.715 
kilograms.  An  analysis  of  the  clover  hay  used  in  this  period  showed 
but  slight  variations  from  that  of  the  preceding  period.  The  com- 
position of  the  maize  meal  and  of  the  feces  was :  — 


Water 

Ash 

Protein       .... 
Non-protein   .     .     . 
Crude  fiber     .     .     . 
Nitrogen-free  extract 
Ether  extract 


FECES 
% 

81.91 
1.77 
3.66 

6.51 
5-71 
0.44 


Il6  NUTRITION  OF  FARM  ANIMALS 

The  digestible  matter  contained  in  the  total  ration,  computed 
exactly  as  in  the  previous  example,  was  as  shown  in  the  first  part 
of  Table  21.  If,  now,  it  be  assumed  that  the  digestibility  of  the 
clover  hay  was  unaltered  by  the  addition  of  the  maize  meal,  it  is 
possible  to  compute  how  much  of  each  kind  of  digestible  matter  (pro- 
tein, crude  fiber,  nitrogen-free  extract,  etc.)  in  the  total  ration  was 
derived  from  the  hay;  the  remainder,  therefore,  must  have  come 
from  the  maize  meal  and  by  comparison  with  the  total  amounts 
present  in  the  latter  the  percentage  digestibility  is  computed. 

It  is  evident  that  the  determination  of  the  digestibility  of  a  con- 
centrate in  this  way  is  less  accurate  than  that  of  a  feed  which  can  be 
given  by  itself.  The  assumption  that  the  digestibility  of  the  roughage 
is  not  changed  is  unproved  and  probably  not  strictly  correct.  More- 
over, any  errors  arising  from  this  source  and  likewise  all  the  errors  in 
weighing  and  analysis  are,  by  the  method  of  calculation,  assigned  to 
the  concentrate.  The  writer  has  shown  1  that  the  range  of  uncer- 
tainty thus  introduced  may  be  very  wide.  It  will  evidently  be 
greatest  when  the  proportion  of  concentrate  to  roughage  is  least  and 
will  affect  most  those  ingredients  of  the  concentrate  which  are  present 
in  the  smallest  proportion,  such  as  crude  fiber  and  often  ether  extract. 
In  extreme  cases,  absurd  results  are  sometimes  obtained,  such  as 
negative  digestibility  or  a  digestibility  greater  than  100  per  cent. 

162.  Laboratory  determination  of  digestibility.  —  Actual 
digestion  experiments  upon  animals  according  to  the  method 
just  outlined,  while  simple  in  principle,  require  special  facilities 
and  a  considerable  expenditure  of  time.  It  would  obviously 
be  very  desirable  to  possess  methods  by  which  the  action  of  the 
digestive  fluids  of  the  body  could  be  imitated  in  the  laboratory 
and  the  digestibility  of  feeds  thus  determined  in  a  simpler 
and  more  expeditious  manner. 

Numerous  attempts  have  been  made  to  solve  this  problem, 
but  as  yet  a  satisfactory  method  has  been  worked  out  only 
for  protein,  while  attempts  to  devise  similar  methods  for  the 
non-nitrogenous  ingredients  of  feeding  stuffs  have  not  yet 
proven  successful.  The  method  for  protein  is  based  upon 
suggestions  made  long  ago  by  Stockhardt  and  by  Hofmeister, 
but  was  first  put  into  practical  form  by  Stutzer.2  It  consists 
in  treating  the  feed  with  a  solution  of  pepsin  and  hydrochloric 
acid  under  specified  conditions  and  determining  the  undissolved 
nitrogen  in  the  residue.  The  difference  between  this  and  the 

1  Amer.  Jour.  Sci.,  29  (1885),  35-5-      2  Jour.  Landw.,  28  (1880),  195  and  435. 


TABLE  21.  —  COM 

DIGESTIO 

PUTATION    C 

h 

N  AND   RESORPTION 

F  THE  DIGESTIBILITY  OF 

\O    GO       rt  OO     vO     H       1000 

II7 
A  CONCENTRATE 

r-»  to 

rf    JO 

CN 

oi    0 

M       CO 

ON    CM 
M    00 

CN      O 

00    & 
CO 

M 

II 

3« 

O    r- 

ts.«0 

H      H 

0    0 

COOO 

to  r^ 

•<3-  to 

H      M 

M      O 

co  O 
O    t- 
co 

M      CN 
t^     CO 
<N    00 

ON    M 

PI 

O     ON 

O      H 

ON    O 

-    o 

ON    CO 

Svg 

CO    H 
CO   10 

M 

M       TJ" 
OO       -5J- 

1>-    CN 

covO 

]]l 

rj-  vq 

ON    Tj- 

O      CN 

t^-  CO 

CO   co 

00     •"*• 

CO*      ON 
ON    IO 

M 

t? 

ON    IO 

CO    ON 
M 

§u&    . 

§SS3 

OO   O 

-t   t- 

tr^   co 

to 

oo   r- 

ON    M 
COCO 
H      CS 

<N      T|- 

00    •* 

t^»    ON 
CO 

IO    ON 
CN 

pi 

S"5> 

co   t^ 

M 

CO    <N 

IO  00 

H    vO 

M      IO 

M 

M    VO 
t-^.    (N 
TJ-     CN 
IO    IO 

CM     CO 

fcW    " 

co   0 

CO    | 

CO    CO 

O     O 

vO    O 

CO    M 

vd       1 

•<$•    CO 

2  8 

PH  H  Q 

10  O 

to    CO 

CN      CO 

ON    rj- 

CO      <N 

O    to 

•*    CO 

r^  co 

H      r^ 

•*   O 

rj-    CN 

CN 

P| 

00  00 

vO     CO 

CO    O 

co  vO 

rt    0 
t^    O 

<N     ro 

to   co 
CO   Tf 

\O       M 

<N      CO 
10    O 

ON  OO 

M 

**•  o 

vO     0 

0      H 

10    CO 

CN      Tj- 

H      O 
M       IO 

^      5 

2^ 

ONOO   , 
H 

><  w    w 

^00 

CM    •rh 

00     co 

O 
to  to 

l>-    H 

10    ON 

H 

co 

vO     O 
CO    to 

M     rt- 

cO   co 

ro   t-- 
vO     10 

O     M 

to  O 

0      ON 
IO    M 

• 

Digested  from  maize  meal 
Percentage  digestibility  .  . 

g 

'     ^ 

•  •    •  --81 
.  .   .  .  ».a 

x|  |  S  1  1 

Il8  NUTRITION  OF   FARM   ANIMALS 

total  nitrogen  of  the  feed  represents,  of  course,  the  amount  of 
nitrogenous  matter  which  has  been  dissolved  and  which,  there- 
fore, is  regarded  as  digestible. 

Comparisons  by  Kellner,1  Pfeiffer,2  G.  Kiihn 3  and  others  between 
the  natural  and  artificial  digestion  of  protein  have  shown  that  the 
former  method  gives  lower  results  on  account  of  the  presence  in  the 
feces  of  nitrogenous  excretory  products  (154,  158),  but  that  when  a 
correction  is  made  for  the  latter  in  the  manner  indicated  on  a  subse- 
quent page  (166)  the  results  of  the  two  methods  show  a  substan- 
tial agreement.  In  other  words,  the  method  of  artificial  digestion 
shows  with  a  good  degree  of  accuracy  the  true  as  compared  with  the 
apparent  digestibility  (163,  167)  of  the  protein. 

163.  Influence  of  excretory  products  on  apparent  digesti- 
bility. —  Since  the  digestion  experiment  as  ordinarily  conducted 
ignores  the  presence  in  the  feces  of  excretory  products,  the  re- 
sults obtained  by  its  use  will  necessarily  be  too  low,  since  sub- 
stances are  reckoned  as  undigested  ingredients  which  really  are 
not  such.     Obviously,   the  ingredients  most  affected  by  this 
error  will  be  those  which,  on  the  one  hand,  are  contained  in 
the  feed  in  the  smallest  proportion  and  which,  on  the  other 
hand,    are   relatively   most    abundant    among    the    excretory 
products  in  the  feces.     These  ingredients  are,  when  the  or- 
dinary scheme  of  feeding  stuffs  analysis  is  followed,  ash,  ether 
extract   and  'nitrogenous   substances.     As   regards   the   crude 
fiber,  on  the  other  hand,  this  error  is  absent,  since  obviously 
no  crude  fiber  is  included  among  the  excretory  products,  and  it 
seems  probable  that  substantially  the  same  thing  is  true  of 
the  nitrogen-free  extract. 

164.  Digestibility    of    ash    ingredients.  —  Certain    ash    in- 
gredients,  particularly   iron,    calcium,    magnesium   and   phos- 
phorus, are  largely  or  wholly  excreted  from  the   body  in  the 
feces  (199).     Furthermore,  the  resorption  of  the  ash  ingredients 
of  the  digestive  juices  may  not  be  complete  and  these  residues 
may  be  added  to  the  ash  content  of  the  feces.     The  ordinary 
digestion  experiment,  therefore,  affords  little  information  as  to 
the  extent  to  which  the  ash  ingredients  of  the  feed  are  actually 

1  Centbl.  Agr.  Chem.,  9  (1880),  763. 

2  Jour.  Landw.,  33  (1885),  149;   34  (1886),  425. 
"Landw.  Vers.  Stat.,  44  (1894),  188. 


DIGESTION  AND   RESORPTION  1 19 

digested  and  resorbed  and  this  fact  constitutes  a  serious  dif- 
ficulty in  the  study  of  the  ash  metabolism. 

165.  Digestibility  of   ether  extract.  —  Among  the  excretory 
products   contained   in   the    feces   are    included   ether-soluble 
substances,  especially  those  derived  from  unresorbed  bile  con- 
stituents.    While  their  total  amount  is  small,  the  feed  of  farm 
animals  is  also  usually  poor  in  ether  extract  and  consequently 
the  error  in  the  computation  of  the  percentage  digestibility 
may  be  relatively  large.     Indeed,  not  a  few  instances  are  on 
record  in  which  the   ether  extract  of  the  feces  has  exceeded 
that  of  the  feed.    Little  definite  knowledge  is  available,  however, 
as  to  the  actual  extent  of  the  error  thus  introduced,  but  it  is  of 
relatively  less  importance  in  view  of  the  small  role  which  fat 
plays  in  the  ordinary  rations  of  farm  animals. 

166.  Digestibility  of  nitrogenous  substances.  —  Most  of  the 
excretory  products  in  the  feces  (154)  are  nitrogenous  substances 
and  it  is  particularly  with  reference  to  their  influence  upon  the 
determination  of  the  digestibility  of  the  nitrogenous  constituents 
of  feeding  stuffs  that  investigation  has  been  active.     That  they 
may  seriously  affect  it  is  evident  from  the  results  obtained  in 
numerous  experiments  upon  feeding  stuffs  poor  in  protein,  such 
as  straw,  in  which  a  negative  digestibility  of  the  crude  protein 
has  been  observed, — i.e.,  in  which  the  feces  have  contained 
more  nitrogen  than  the  feed.     Moreover,   experiments  upon 
rations  containing  no  nitrogen  at  all  have  shown  that  under 
these  conditions  nitrogen  continues  to  be  excreted  in  the  feces. 

Various  methods  for  distinguishing  between  the  nitrogen  of 
feed  residues  and  the  nitrogen  of  excretory  products  have  been 
proposed  at  different  times,  but  the  one  which  has  proved  most 
satisfactory  and  which  is  generally  accepted  at  present  is  based 
upon  the  solubility  of  the  nitrogenous  excretory  products  in 
the  solution  of  pepsin  and  hydrochloric  acid  employed  in  Stut- 
zer's  method  for  the  laboratory  determination  of  the  digesti- 
bility of  protein  described  in  a  previous  paragraph  (162). 

By  treatment  of  a  sample  of  the  fresh  feces  with  such  a  solu- 
tion under  proper  conditions  the  excretory  nitrogenous  products 
are  dissolved,  and  it  has  been  shown  that  very  close  agreement 
can  be  obtained  between  the  artificial  and  natural  digestion  of 
protein  if  the  comparison  in  the  latter  case  be  made  upon  the 
pepsin-insoluble  nitrogen  of  the  feces.  In  other  words,  the 


120  NUTRITION  OF  FARM  ANIMALS 

pepsin-insoluble  nitrogen  of  the  feeds  appears  quantitatively 
in  the  feces,  where  it  may  be  regarded  as  representing  indigesti- 
ble feed  protein,  while  the  pepsin-soluble  nitrogen  of  the  feces 
is  contained  in  the  excretory  products,  part  of  which  are  protein 
(mucus,  epithelium,  etc.)  and  part  non-protein  (residues  of 
digestive  fluids,  etc.).  An  approximate  correction  for  the 
amount  of  nitrogenous  excretory  products  may  also  be  com- 
puted by  the  use  of  Pfeiffer's  factor  of  0.4  gram  nitrogen  per 
100  grams  digested  dry  matter. 

167.  Apparent  digestibility.  —  When  the  results  of  the  or- 
dinary digestion  experiment  are  corrected,  in  the  manner  just 
outlined,  for  the  nitrogenous  excretory  products  in  the  feces 
we  get  an  approximation  to  the  true  percentage  digestibility 
of  the  protein,  while,  as  regards  the  carbohydrates,  the  error, 
as  has  been  shown,  is  probably  not  serious,  at  least  for  herbivora. 

There  is  another  way  of  looking  at  the  matter,  however. 
The  intestinal  products  found  in  the  feces  are,  in  effect,  part 
of  the  cost  of  digesting  the  feed.  They  represent  the  "  wear 
and  tear  "  of  the  digestive  organs.  The  difference,  then,  be- 
tween feed  and  feces  will  show  the  net  gain  to  the  animal  from 
the  digestion  of  the  feed,  that  is,  it  will  show  how  much  more 
proteins,  carbohydrates,  etc.,  the  body  has  at  its  disposal  than 
it  would  have  had  if  the  feed  had  not  been  given.  From  this 
point  of  view,  we  may  speak  of  the  digestibility  as  ordinarily 
determined  as  the  apparent  digestibility,  and  regard  it  as  a 
measure  (approximately  at  least)  of  the  matter  gained  by  the 
body  from  the  consumption  of  the  feed.  For  many  purposes, 
therefore,  the  apparent  digestibility  gives  a  better  basis  for  com- 
paring the  values  of  feeding  stuffs  than  does  the  real  digestibility. 
It  was  from  this  point  of  view  that  Atwater  1  proposed  the  use 
of  the  term  availability  as  the  equivalent  of  what  is  here  called 
apparent  digestibility. 

168.  Composition    of    digested    crude    fiber.  —  The    crude 
fiber  (109)  consists  of  the  cellulose  of  the  plant  together  with 
varying  amounts  of  pentosans  and  of  lignin  and  other  incrusting 
substances,  the  ratio  of  which  to  the  cellulose  increases  with 
the  maturity  of  the  plant.     Cellulose  itself  seems  to  be  attacked 
and  dissolved  with  comparative  ease  by  the  organisms  of  the 
rumen  and  the  coecum,  and  the  same  is  probably  true  of  the 

1  Rpt.  Conn.  (Storrs)  Expt.  Sta.,  1897,  p.  156. 


DIGESTION  AND   RESORPTION  1 21 

pentosans,  but  lignin  appears  to  be  much  less  readily  digested 
and  some  of  the  other  incrusting  materials  not  at  all.  As  a 
consequence,  a  computation  based  on  the  elementary  composi- 
tion of  the  crude  fiber  of  the  feed  and  of  the  feces  respectively 
and  on  the  percentage  of  the  former  which  is  digestible  shows 
the  digested  portion  to  have  approximately  the  ultimate  compo- 
sition and  heat  of  combustion  of  cellulose. 

This  is  by  no  means  equivalent  to  saying  that  the  digested 
crude  fiber  consists  only  of  cellulose.  The  variations  between 
the  results  in  individual  experiments  show  clearly  that  this 
cannot  be  the  case  and  doubtless  more  or  less  of  the  pentosans 
and  other  ingredients  of  the  crude  fiber  are  attacked  to  some 
extent,  but  it  is  nevertheless  evident  that  the  cellulose  is  the 
chief  constituent  digested.  Neither  is  the  heat  of  combustion 
of  the  digested  portion  in  any  sense  a  measure  of  the  energy 
which  it  can  supply  for  the  bodily  activities,  as  will  appear 
more  clearly  later. 

169.  Composition   of   digested   nitrogen-free   extract.  —  By 
a  difference  calculation  identical  in  principle  with  that  em- 
ployed for  crude  fiber  but  somewhat  more  complicated  in  its 
details  and  involving  certain  assumptions,  it  has  been  shown 
that  the  digested  portion  of  the  nitrogen-free  extract  has  also 
approximately   the   composition   and   heat   of   combustion   of 
starch  or  cellulose.     Even  less  than  in  the  case  of  crude  fiber 
does  this  fact  serve  to  fix  with  any  definiteness  the  nutritive 
value  of  the  digested  portion.     We  know  that  the  nitrogen- 
free  extract  of  feeding  stuffs  includes  a  great  variety  of  sub- 
stances (110),  some  of  which,  like  starch,  are  digested  in  the 
narrower  sense  of  the  word  while  many  others,  like  the  hemi- 
celluloses,  pentosans,  etc.,  are  fermented  rather  than  digested. 
The  data  as  to  the  composition  of  the  digested  portion  indicate, 
it  is  true,  that  it  consists  chiefly  of  carbohydrates,  but  on  ac- 
count of  the  small  range  of  ultimate  composition  shown  by  these 
substances  no  indications  are  afforded  of  the  specific  carbohy- 
drates present. 

170.  Digestible   carbohydrates.  —  Since  both   the   digested 
crude  fiber  and  the  digested  nitrogen-free  extract  have  approxi- 
mately an  ultimate  composition  corresponding  to  the  formula 
C6HioO5,  it  has  become  customary  in  estimating  the  nutritive 
values  of  feeding  stuffs  to  add  together  the  digestible  portions 


122  NUTRITION  OF  FARM  ANIMALS 

of  these  two  groups  and  to  designate  the  sum  as  the  "  digestible 
carbohydrates."  The  practice  dates  from  the  early  experi- 
ments of  HennebergandStohmann,  but  in  the  light  of  our  present 
knowledge  has  little  justification. 

In  the  first  place,  as  just  stated,  the  agreement  in  composition 
is  but  approximate  and  variable.  The  essential  point,  however, 
is  that  a  digestion  experiment  can  show  simply  that  a  certain 
amount  of  material  of  a  certain  ultimate  composition  has  failed 
to  reappear  in  the  feces  of  the  animal,  and  by  itself  affords  no 
information  as  to  the  changes  which  it  has  undergone  nor  as 
to  the  nature  of  the  products  actually  resorbed.  As  a  matter 
of  fact,  a  large  share  of  the  "  digested  "  portion  of  these  two 
groups,  especially  in  the  case  of  ruminants,  has  been  fermented 
rather  than  digested.  A  considerable  proportion  of  it  has  been 
excreted  in  gaseous  form  as  carbon  dioxid  and  methane  and 
only  a  residue  of  organic  acids  has  been  resorbed.  Such  being 
the  case,  the  term  digestible  carbohydrates  is  a  palpable  mis- 
nomer. 

171.  Digested  ether  extract.  —  No  determinations  of  the 
composition  of  the  digested  ether  extract  similar  to  those  on 
crude  fiber  have  been  made,  but  a  few  determinations  of  the 
heat  of  combustion  of  the  digested  extract  are  reported  by 
Kellner.1  The  presence  in  the  feces  of  ether  soluble  excretory 
products  (165)  interferes  with  the  accuracy  of  such  a  comparison 
and  its  results  must  be  regarded  as  approximations.  The  ether 
extract  of  the  feces  was  found  to  have  a  higher  heat  of  combus- 
tion than  that  of  the  hay  fed,  doubtless  on  account  of  the 
presence  in  the  former  of  the  indigestible  waxes,  etc.,  while 
the  computed  heat  of  combustion  of  the  digested  portion  was 
distinctly  lower  than  that  for  pure  fats,  which  average  about 
9.5  Cals.  per  gram.  The  heats  of  combustion  per  gram  on  the 
average  of  five  trials  were :  — 

Ether  extract  of  hay  ....  9.194  Cals. 
Ether  extract  of  feces  ....  9.824  Cals. 
Digested  ether  extract  .  .  .  .  8.322  Cals. 

1  Landw.  Vers.  Stat.,  47  (1896),  301. 


CHAPTER  IV 
CIRCULATION,    RESPIRATION   AND    EXCRETION1 

§  i.   CIRCULATION 

172.  Distribution  of  nutrients.  —  The  digestive  changes  by 
which  the  ingredients  of  the  feed  are  prepared  for  the  nutrition 
of  the  organism  take  place  outside  the  body  proper  (113).     In 
order  that  the  products  formed  shall  serve  their  purpose  they 
must  not  only  be  taken  up  into  the  body  by  the  processes  of 
resorption  described  in  the  preceding  chapter  but  they  must 
be  distributed  through  it,  so  that  each  of  its  myriad  cells  may 
receive  the  substances  which  it  requires.     The  chief  vehicle  of 
this  distribution  is  the  blood,  into  which  the  resorbed  nutrients 
are  transferred,  directly  or  indirectly,  and  the  distribution  is 
accomplished  by  means  of  the  circulation  of  the  blood,  dis- 
covered by  Harvey  in  1621. 

173.  The  blood.  —  This  familiar  but  highly  complex  fluid 
serves  a  variety  of  purposes,  being  not  only  the  carrier  of  the 
resorbed  feed  ingredients  to  the  tissues  and  cells  but  transmitting 
to  them  the  equally  necessary  oxygen  and  carrying  away  the 
products  of  their  activity  to  be  used  in  other  parts  of  the  body 
or  to  be  excreted. 

The  blood  of  the  higher  animals  is  a  thickish,  somewhat  viscid 
fluid,  having  a  faint  but  peculiar  odor,  a  slightly  salt  taste  and 
a  color  varying  from  bright  to  dark  red.  It  is  somewhat  heavier 
than  water  (sp.  gr.  1.045-1.075),  and  contains  about  21  per 
cent  of  total  solids.  Under  the  microscope  it  is  seen  to  consist 
of  a  clear  fluid,  the  plasma,  holding  in  suspension  a  vast  number 
of  small,  solid  bodies,  the  corpuscles.  The  latter  are  of  two 
kinds,  known  as  the  red  corpuscles,  or  ery throcytes,  and  the  white 
corpuscles,  or  leucocytes. 

1  Only  such  a  very  general  consideration  of  the  outlines  of  these  functions  as  seems 
essential  for  a  proper  comprehension  of  the  phenomena  of  metabolism  and  of  the 
processes  of  nutrition  is  attempted  here.  For  a  more  complete  elementary  discus- 
sion, the  reader  is  referred  to  Hough  and  Sedgwick's  The  Human  Mechanism, 
Chapters  IX,  X  and  XI,  and  for  further  details  to  the  larger  treatises  on  physiology. 

123 


I24 


NUTRITION  OF  FARM  ANIMALS 


174.  Red  blood  corpuscles.  —  These  are  by  far  the  more 
numerous  of  the  two  kinds.     In  man  they  are  round  like  "a  coin 
but  thicker  at  the  edges  than  in  the  center,  and  have  a  diameter 
of  0.0060-0.0085  millimeter.     Their  number  is  enormous,  being 
estimated  at  4  to  5^  millions  per  cubic  millimeter  of  blood. 
To  them  the  color  and  opacity  of  the  blood  are  due. 

The  corpuscles  of  each  species  of  animal  are  peculiar  to  it,  both 

as  to  shape  and  size,  but 
their  general  characteristics 
are  the  same  in  all.  Those 
of  most  animalsaresmaller 
than  those  of  man.  Each 
corpuscle  is  a  cell,  having 
no  nucleus  but  containing 
as  its  characteristic  ingre- 
dient the  conjugated  pro- 
tein haemoglobin  to  which 
the  red  color  of  the  blood 
is  due.  Haemoglobin  is  a 
crystalline  substance  and 
it  has  recently  been  shown 
by  Reichert  that  the 
haemoglobin  of  each  spe- 
cies of  animal  has  its  spe- 
cific crystalline  form  and 
properties. 

175.  White   blood   corpuscles.  —  The  white  corpuscles   are 
colorless,   nucleated    cells    which    are    not    confined    to    the 
blood  but  which,  by  means  of  ameboid  movements,  are  able 
to    pass   through   the    walls    of    the    blodd    vessels    and    the 
lymph  spaces  of  connective  tissue  as  the  so-called  "  wander- 
ing   cells."      They    have    important    functions,    especially    in 
protecting   the  body  from  disease,  but  need   not   be  further 
considered  here. 

176.  Blood  platelets.  —  In  addition  to  the  two  kinds  of  cor- 
puscles, the  blood  contains  more  minute  nucleated  cells,  rang- 
ing  in  diameter  from  0.0003-0.0005  millimeter,  called  blood 
platelets,  or  thrombocytes.     They  are  much  more  abundant 
than  the  white  corpuscles  and  are  thought  to  be  concerned  in 
the  coagulation  of  the  blood. 


FIG.  16.  —  Blood  corpuscles. 

Above  are  shown  nine  red  corpuscles,  highly  mag- 
nified; below,  less  highly  magnified,  the  appearance 
of  the  blood  soon  after  being  drawn.  (Hough  and 
Sedgwick,  The  Human  Mechanism.) 


CIRCULATION,   RESPIRATION  AND   EXCRETION       125 


177.  Blood  plasma.  —  This  very  complex  fluid  contains,  be- 
sides about  90  per  cent  of  water,  a  great  variety  of  substances, 
the  most  prominent  of  which  are  the  proteins,  of  which  two 
groups  are  recognized,  viz.,  two  or  more  serum  globulins  and 
the  so-called  serum  albumin,  which  is  probably  not  a  single 
chemical    individual.     Plasma    contains    also    approximately 
0.1-0.15  Per  cent  °f  dextrose,  from  o.i  to  as  much  as  i.o  per 
cent  of  fat,  usually  in  some  soluble  form  (243),  a  great  variety 
of  so-called  extractives  which  are  in  part  waste  products  of  cell 
action,  and  about  i  per  cent  of  mineral  ingredients. 

178.  Coagulation.  —  When  blood  is  drawn  from  the  body  it 
usually  coagulates  or  clots  within  a  few  minutes.     The  coagu- 
lating substance  is  a  globulin  called  fibrinogen  and  its  coagulation 
is  an  enzymatic  reac- 
tion  brought  about 

by  a  ferment,  throm- 
bin,  believed  to  be 
derived  from  the 
blood  platelets  by 
a  very  complicated 
process.  The  coag- 
ulated protein  con- 
stitutes the  so-called 
blood  fibrin,  which 
entangles  within  it- 
self the  corpuscles, 
producing  the  famil- 
iar blood  clot.  While 
the  clot  is  very  bulky 
the  dry  blood  fibrin 
amounts  to  only  0.2- 
0.3  per  cent  of  the 
weight  of  the  blood. 

179.  The  heart.— 
The  blood  is  distrib- 
uted to  all  parts  of 


FIG.  17.  —  Diagram  of  mammalian  heart. 


a,  Left    ventricle,      b,  Right    ventricle,      c.  Left    auricle. 
d,    Right    auricle.      /,    Aorta.       gg,    Pulmonary     arteries. 
-       ,       ,     ,  -     op..  Pulmonary  veins.     (Smith,  Physiology  of  the  Domestic 

the  body  by  means  ol    Animals.) 

a    most    interesting 

organ,  the  heart,    which    is    in   effect   a   living   force   pump. 

Figure  17  shows  diagrammatically  the  structure  of  the  mam- 


126  NUTRITION  OF  FARM  ANIMALS 

malian    heart,    which   is   substantially  the  same  in   all  farm 
animals. 

It  is  divided  by  an  impervious  partition  into  a  right  and  left 
half,  and  each  of  these  is  subdivided  by  a  cross  partition  into 
two  chambers,  communicating  with  each  other  by  a  valve  in 
the  dividing  wall.  The  upper  and  smaller  of  these  divisions 
are  known  as  the  right  and  left  auricles,  and  the  lower  and 
larger  as  the  right  and  left  ventricles.  Into  these  cavities  of  the 
heart  open  several  large  blood  vessels,  whose  mouths  are  closed 
with  valves  so  arranged  that  the  blood  can  only  flow  into  the 
auricles  and  out  of  the  ventricles. 

180.  Arteries.  —  The  blood  vessels  which  conduct  the  blood 
from  the  heart  to  the  various  organs  of  the  body  are  called 
arteries  and  may  be  described  as  tubes  with   strong,   elastic 
and  contractile  walls,  to  withstand  the  force  with  which  the 
blood  is  pumped  into  them  by  the  heart.     Their  walls  consist 
of  an  outer  layer  of  elastic  and  connective  tissue,  a  middle  layer 
of  muscular  tissue  and  an  inner  layer  of  epithelium.     The  ar- 
teries originate  in  the  aorta  (h,  Fig.  18),  which  receives  the  blood 
from  the  left  ventricle,  and  as  they  extend  farther  and  farther 
from  the  heart  subdivide  and  throw  off  branches  to  the  various 
organs,  the  more  minute  of  which  are  called  arterioles,  finally 
ending  in  the  capillaries. 

181.  Capillaries.  —  The  capillaries  are  exceedingly  minute 
blood  vessels  which  penetrate  all  the  tissues  of  the  body  and 
form  the  connecting  link  between  the  arteries  and  veins.     Their 
walls  are  thin  and  delicate,  and  through  them  the  nutritive  mat- 
ters of  the  blood  pass  out  into  the  tissues  while  the  waste  prod- 
ucts of  cell  activity  pass  from  the  tissues  into  the  blood.     In 
Fig.  1 8,  n  represents  the  capillaries  of  the  posterior  part  of  the 
body,  o  those  of  the  stomach  and  intestines,  t  those  of  the  kid- 
neys, p  those  of  the  liver,  and  m  those  of  the  anterior  part  of 
the  body.     The  capillaries  gradually  unite  again  into  larger 
vessels,  the  veins,  which  convey  the  blood  back  to  the  heart 
and  lungs. 

182.  Veins.  —  The  veins  are  tubular  vessels  somewhat  similar 
to  the  arteries  but  with  weaker  and  non-elastic  walls,  the  pres- 
sure of  the  blood  on  them  being  slight,  owing  to  the  interposi- 
tion of  the  capillaries  between  them  and  the  arteries  and  to  the 
fact  that  their  total  cross  section  is  greater  than  that  of  the 


CIRCULATION,   RESPIRATION   AND   EXCRETION       127 


arteries.  To  prevent  any  possible  flowing  back  of  the  blood, 
the  veins  are  provided  at  intervals  with  valves  which  permit  the 
blood  to  pass  toward  the  heart 
but  not  in  the  opposite  direc- 
tion. The  smaller  veins  unite 
to  form  larger  ones,  and  finally 
empty  their  contents  through 
two  branches  into  the  right 
auricle  of  the  heart.  From 
the  capillaries  of  the  intestines 
the  blood  carrying  the  re- 
sorbed  nutrients  passes  through 
the  portal  vein,  s,  to  the  liver,  p, 
is  there  distributed  through 
another  system  of  capillaries 
and  then  rejoins  the  blood 
from  the  extremities  through 
the  hepatic  vein,  u.  Into  the 
branch,  k,  coming  from  the 
head  and  anterior  parts  of  the 
body,  the  nutrients  which  are 
resorbed  by  the  lacteals  enter 
by  way  of  the  thoracic  duct. 
183.  Course  of  the  blood.  - 
The  blood  returning  through 
the  veins  from  the  extremities 
of  the  body  to  the  heart  enters 
first  the  right  auricle  (a,  Fig. 
1 8),  through  two  large  veins, 
k  and  /,  coming  from  the  an- 
terior and  posterior  parts  of 
the  body.  The  auricle  then 
contracts  and  the  blood,  being 
prevented  from  returning  into 
the  veins  by  the  valves  at  their 

mouths,   is  forced   through   the        FlG-  l8-  ~  Scheme    of    circulation    of 
,        .  '  ,,  ....  11  •,       blood.       (Armsby,    Manual    of    Cattle 

valve  in  the  partition  wall  into   Feeding.) 

the  right   ventricle,  b.     This, 

in   turn,   contracting,    the   blood,   prevented   as   before  by  a 

valve  from  turning  back  in  its  course,  is  forced  out  of  the 


128  NUTRITION  OF  FARM  ANIMALS 

ventricle  into  the  pulmonary  artery,  c,  which  divides  into  two 
branches  leading  to  the  capillaries  of  the  right  and  left  lungs, 
d,  d.  The  entrance  to  this  blood  vessel,  like  that  of  the  others, 
is  provided  with  a  valve  which  prevents  the  return  of  the  blood. 
The  blood,  after  passing  through  the  lung  capillaries,  returns 
to  the  left  auricle,  /,  through  the  pulmonary  veins,  represented 
by  e.  The  auricle  then  contracting,  sends  the  blood  into  the 
left  ventricle,  g,  which,  in  its  turn,  contracts  powerfully  and 
expels  the  blood  into  one  large  vessel,  the  aorta,  h.  The  aorta, 
soon  after  leaving  the  heart,  divides  into  two  branches,  i  and  j, 
and  these  repeatedly  subdivide,  forming  the  arteries  which  carry 
the  blood  to  the  arterioles  and  capillaries,  whence  it  returns 
again  through  the  veins  to  the  right  side  of  the  heart. 

The  passage  of  the  blood  from  the  left  side  of  the  heart  through 
the  body  capillaries  and  back  to  the  right  side  is  called  the 
greater  or  systemic  circulation;  that  from  the  right  side 
of  the  heart  through  the  lung  capillaries,  the  pulmonary  cir- 
culation. 

The  appearance  of  the  blood  in  the  veins  and  arteries  is 
strikingly  different.  In  the  veins  it  has  a  dark,  cherry-red 
color,  but  after  it  has  passed  through  the  lungs  and  is  sent  out 
by  the  heart  to  the  arteries  it  has  a  bright  scarlet  color.  The 
former  is  called  venous,  the  latter,  arterial  blood.  An  exception 
to  this  rule,  that  the  arteries  carry  bright  red  blood  and 
the  veins  dark,  is  found  in  the  pulmonary  circulation,  where, 
of  course,  the  vessels  leading  from  the  heart  to  the  lungs  carry 
venous  blood,  and  those  leading  from  the  lungs  to  the  heart, 
arterial.  Nevertheless,  the  general  nomenclature  is  adhered 
to,  and  the  former  are  called  arteries  and  the  latter  veins.  Ar- 
teries conduct  the  blood  from  the  heart,  veins  toward  it. 

184.  Mechanics  of  circulation.  —  While  it  is  not  uncommon 
to  speak  of  the  flow  of  the  blood,  or  of  the  blood  stream,  sug- 
gesting an  analogy  to  a  brook  or  river,  the  circulation  is  not  in 
reality  a  flow  of  this  sort  but  resembles  rather  the  movement  of 
the  water  pumped  into  a  hose  by  a  force  pump.  The  heart 
constitutes  the  force  pump  and  the  arteries  correspond  to  the 
hose.  The  powerful  muscular  contraction  of  the  ventricle 
drives  the  blood  into  the  arteries  by  successive  impulses,  as  the 
water  is  driven  into  the  hose  by  the  pump.  If  the  end  of  the 
hose  were  left  open  the  water  would  issue  in  a  series  of  spurts 


CIRCULATION,   RESPIRATION  AND   EXCRETION       129 

corresponding  to  the  strokes  of  the  pump.  By  the  addition  of 
a  nozzle  of  smaller  diameter  than  the  hose  this  intermittent 
outflow  is  converted  into  a  steady  stream.  The  resistance  of 
the  nozzle  to  the  passage  of  the  water  gives  rise  to  a  pressure 
which  stretches  the  walls  of  the  hose,  and  their  elastic  force 
maintains  the  flow  between  the  strokes  of  the  pump. 

Substantially  the  same  conditions  exist  in  the  body.  The 
walls  of  the  arteries  are  elastic  while  the  capillaries  in  which 
the  arteries  terminate  may  be  compared  to  the  nozzle  of  the  hose. 
The  resistance  caused  to  the  flow  of  the  blood  by  these  minute 
channels  tends  to  hold  it  back  and  produces  a  pressure  in  the 
arteries  which,  like  the  pressure  in  the  hose,  causes  a  steady 
movement  of  blood  through  the  capillaries.  In  other  words, 
the  immediate  cause  of  the  motion  of  the  blood  through  the 
capillaries  is  the  elasticity  of  the  arterial  walls.  If  the  latter 
become  weakened  and  lose  their  tone  or  become  hardened  as  in 
old  age  (arteriosclerosis),  the  driving  force  is  lessened  and  the 
circulation  slows  down,  since  the  veins  can  return  blood  to  the 
heart  only  as  fast  as  it  is  forced  through  the  capillaries  by  the 
arterial  pressure.  The  blood  pressure  in  the  arteries,  therefore, 
is  an  important  indicator  of  the  activity  of  the  circulatory  sys- 
tem. The  veins  serve  substantially  as  a  return  system,  the 
blood  being  pushed  along  them  by  the  residual  pressure  from  the 
capillaries,  perhaps  aided  somewhat  by  the  expansion  of  the 
auricle  of  the  heart,  while  valves  prevent  any  backward  flow. 
As  compared  with  the  arterial  pressure,  therefore,  the  blood 
pressure  in  the  veins  is  low. 

185.  The  lymph.  —  The  body  cells  are  not  closely  packed  to- 
gether but  are  imbedded  more  or  less  loosely  in  connective  tis- 
sue (83)  leaving  spaces  between  them  (intercellular  spaces). 
These  spaces  contain  a  colorless  transparent  fluid  called  the 
lymph  which  is  the  real  nutritive  medium  in  which  the  cells 
live.  From  it,  by  means  of  osmosis  through  their  outer  mem-- 
branes  and  perhaps  in  other  ways,  the  cells  derive  the  substances 
required  for  their  vital  activities  and  into  it  they  discharge 
the  waste  products  of  their  action. 

The  lymph  in  its  turn  stands  in  relation  to  the  blood,  from 
which  it  is  separated  by  the  thin  walls  of  the  capillaries.  While 
the  minute  capillaries  penetrate  all  the  tissues  and  convey  blood 
to  all  parts  of  the  body,  it  should  be  understood  that  the  cir- 


130 


NUTRITION  OF   FARM  ANIMALS 


culatory  apparatus  is  a  closed  system.  Even  the  very  thin 
delicate  walls  of  the  capillaries  are  continuous  and  the  blood 
does  not  come  into  direct  contact  with  the  living  cells,  except, 
of  course,  those  lining  the  blood  vessels.  The  accompanying 
diagram  (Fig.  19)  illustrates  schematically  the  anatomical  re- 
lations of  the  cells,  intercellular  spaces,  capillaries  and  lym- 
phatics, A  representing  a  minute  artery,  or  arteriole,  subdi- 
viding into  capillaries  which  are  reunited  to  form  the  small 
vein  V.  Through  the  capillary  walls  the  nutritive  substances 
contained  in  the  blood  pass,  partly  by  osmosis  and  partly  by 


FIG.  19.  —  Relation  of  cells  to  blood  vessels  and  lymphatics.     (Hough  and 
Sedgwick,  The  Human  Mechanism.) 

filtration,  into  the  lymph  to  maintain  its  stock,  while  the  waste 
products  of  cell  action  pass  in  the  opposite  direction  into  the 
blood  and  are  carried  off. 

186.  Lymphatics.  —  In  the  intercellular  spaces  there  orig- 
inates another  set  of  minute  vessels,  the  lymphatics,  which 
unite  like  the  capillaries  to  form  larger  ones  (L  in  Fig.  19)  and 
finally  form  two  main  lymphatic  trunks,  the  thoracic  duct 
and  the  small  lymphatic  trunk,  which  empty  into  the  great  veins 
near  the  heart.  The  lacteals  of  the  intestinal  villi,  through  which 
the  fats  are  chiefly  resorbed,  belong  to  the  lymphatic  system. 


CIRCULATION,   RESPIRATION  AND   EXCRETION       131 

In  the  lymphatics  there  is  a  continuous  slow  movement  of  the 
lymph  from  the  tissues  towards  the  main  trunks,  the  lymphatics, 
like  the  veins,  being  provided  at  intervals  with  valves  prevent- 
ing a  backward  flow.  This  lymph 
flow  is  sustained  in  part  by  a 
slightly  greater  pressure  in  the 
lymphatic  spaces  but  largely  by 
the  rhythmic  motions  of  breath- 
ing, and  is  aided  by  muscular 
activity.  Thus,  in  addition  to  the 
exchange  of  substances  between 
the  lymph  and  the  blood  through 
the  walls  of  the  capillaries,  there 
is  a  general  movement  of  the 
lymph  itself  over  the  surface  of 
the  cells  which  tends  to  facilitate 
the  exchanges  between  it  and  the 
protoplasm. 

187.  Adjustment  of  circula- 
tion. — The  activity  of  the  various 
tissues  varies  at  different  times. 
A  muscle,  for  example,  is  some- 
times at  rest  and  sometimes 
actively  contracting.  Conse- 
quently, a  greater  or  less  supply 
of  food  material  and  of  oxygen  will 
suffice  according  to  circumstances, 
and  the  blood  supply  needs  to  be 
regulated  accordingly. 

This  regulation  is  effected  in 
substantially  two  ways.  First, 
when  the  cells  of  any  particular 
tissue  increase  their  activity  they 

consume  more  oxygen  and  give 
„  J  ?  FIG.  20.  —  Mam  lymphatic  trunks 

off  more  waste  products  than  be-  (in  white).    (Hough  and  sedgwick, 
fore,  tending  to  produce  a  relative  The  Human  Mechanism.) 
deficiency  of  the  one  and  an  ex- 
cess of  the  other  in  the  lymph  and  blood.     These  conditions 
bring  about  an  increase  in  the  heart  action  (194),   probably 
by  means  of  a  nerve  stimulus,  so  that  the  amount  of  blood 


132  NUTRITION  OF  FARM  ANIMALS 

passing  through*  the  heart  is  increased  and  a  more  abundant 
supply  of  it  reaches  the  active  tissues.  Second,  there  may 
be  a  partial  shunting  of  the  blood  supply  from  one  region 
of  the  body  to  another  as  one  set  of  organs  or  another  calls 
for  a  larger  amount.  This  is  accomplished  through  the  agency 
of  the  middle  or  muscular  coat  of  the  arterioles,  controlled  by 
the  so-called  vaso-motor  nerves.  When  a  larger  supply  of  blood 
is  called  for  in  the  muscles,  for  example,  these  fibers  relax  and 
allow  the  arterioles  to  enlarge,  thus  reducing  the  resistance 
offered  to  the  blood  flow  and  allowing  the  arterial  pressure  to 
force  blood  into  the  capillaries  more  rapidly.  To  compensate 
for  this  there  is  a  contraction  of  the  arterioles  of  the  internal 
organs,  especially  of  the  abdominal  organs,  resulting  in  a  di- 
minished blood  supply.  The  effect  of  the  performance  of  work 
upon  digestion,  discussed  in  Chapter  XVI  (721),  is  possibly 
connected  with  this  effect  upon  the  blood  flow.  On  the  other 
hand,  after  a  hearty  meal  the  arterioles  of  the  digestive  tract 
relax,  while  the  superficial  blood  vessels  tend  to  contract  and 
the  blood  supply  is  partially  diverted  from  the  surface  tissues 
to  the  internal  organs.  This  power  of  the  body  to  regulate 
the  supply  of  blood  to  different  regions  is  of  special  importance, 
as  will  appear  later  (321),  in  connection  with  the  regulation  of 
the  body  temperature. 

§  2.  RESPIRATION 

188.  The    oxygen    supply.  —  By    means    of    the   processes 
described  in  the  preceding  section  the  nutritive  materials  de- 
rived from  the  feed  and  taken  up  by  the  intestinal  capillaries 
and  lacteals  are  distributed  to  the  various  tissues  and  cells. 
Equally  necessary  with  a  supply  of  feed  materials  to  the  living 
cells,  however,  is  a  supply  of  oxygen,  and  this  another  set  of  or- 
gans, those  of  respiration,  are  engaged  in  furnishing  to  the  blood 
through  another  set  of  capillaries  for  transmission  to  the  cells. 

189.  The  lungs.  —  The  transfer  of  oxygen  from  the  air  to  the 
blood  is  effected  in  the  lungs,  which,  with  the  heart  and  large 
blood  vessels,  fill  the  cavity  of  the  thorax,  or  chest.     This  cav- 
ity is  enclosed  on  the  sides  by  the  ribs  and  their  connections, 
forming  the  chest  walls,  and  is  separated  from  the  abdominal 
cavity,  containing  the  digestive  organs,  by  a  strong,  arched,  mus- 


CIRCULATION,   RESPIRATION  AND   EXCRETION       133 


cular  partition,  convex  toward  the 
chest,  the  diaphragm.  The  air 
enters  the  lungs  through  the 
trachea,  or  windpipe,  from  the 
mouth  and  nostrils.  The  trachea, 
after  reaching  the  chest,  divides 
into  two  branches,  or  bronchi, 
one  leading  to  the  right  and  one 
to  the  left  lung.  Each  bronchus 
subdivides  repeatedly  into  a 
multitude  of  fine  tubes,  the 
smallest  of  which  are  called  bron- 
chioles (little  bronchi),  each  of 
which  finally  ends  in  an  alveolus, 
the  inner  surface  of  which  is  much  ,  FlG-  "•  ~  AlveoU  of  luns-  (wil- 

111.  ,  ckens,  Form  und  Leben  der  Land- 

increased  by  being  arranged   in    wirthschaftiichen  Hausthiere.) 
the   form   of   pits   or   air   cells. 

In  Fig.  21,  c  represents  a  bronchiolus,  aa  two  alveoli  and  bb 
the  air  cells.  Figure  22  shows  diagrammatically  on  a  large 
scale  a  cross  section  of  two  alveoli. 


FIG.  22.  —  Section  of  two  alveoli.     (Hough  and  Sedgwick,  The  Human 
Mechanism.) 


134  NUTRITION  OF   FARM   ANIMALS 

The  walls  of  the  trachea  and  bronchi  consist  of  cartilaginous 
rings  which  prevent  them  from  collapsing.  The  alveoli  and 
bronchioles  are  surrounded  and  bound  together  by  connective 
tissue  consisting  largely  of  elastic  fibers  so  that  the  minute  air 
cavities  of  the  lungs  are  extensible  and  their  walls  elastic.  In 
this  connective  tissue  are  found  the  larger  branches  of  the 
pulmonary  artery  and  pulmonary  vein,  connected  by  a  net- 
work of  capillaries  which  are  spread  out  over  the  inside  of  the 
alveoli  in  direct  contact  with  their  lining  membrane.  Each 
lung  is  enclosed  in  a  double-walled  sack,  the  pleura,  one  wall 
of  which  covers  the  lungs  and  the  other  the  chest  walls  and 
diaphragm,  the  narrow  cavity  between  the  two  being  filled 
with  a  liquid. 

190.  Mechanics  of  breathing.  —  In  breathing,  the  lungs 
themselves  play  an  essentially  passive  role,  the  movement  of 
air  into  and  out  of  them  being  effected  by  changes  in  the  capac- 
ity of  the  chest  brought  about  by  the  movements  of  the  dia- 
phragm and  ribs. 

Since  the  diaphragm  is  convex  toward  the  chest  its  contrac- 
tion tends  to  pull  the  apex  of  the  dome  toward  the  abdomen, 
'thus  increasing  the  volume  of  the  chest  cavity  and  by  pressure 
on  the  digestive  organs  distending  the  abdominal  walls.  When 
the  diaphragm  relaxes  again  the  volume  of  the  chest  is  reduced 
and  the  abdominal  walls  return  to  their  former  position.  This 
type  of  breathing  is  what  is  called  abdominal  breathing. 

The  ribs  pass  obliquely  around  the  chest  from  the  spine  to 
the  breast  bone  (sternum).  By  means  of  the  intercostal 
muscles,  located  between  .them,  the  ribs  can  be  elevated, 
turning  on  their  attachments  to  the  spine  and  sternum,  thus 
increasing  the  diameter  of  the  chest  both  from  side  to  side 
and  from  front  to  back  and  so  increasing  the  capacity  of  the 
chest  cavity.  This  type  of  breathing  is  called  costal,  or  rib, 
breathing. 

The  two  types  of  breathing  are  ordinarily  combined.  By 
their  joint  action  the  size  of  the  closed  pleural  cavity  contain- 
ing the  lungs  is  increased  and  the  atmospheric  pressure  forces 
more  air  into  the  extensible  alveoli  of  the  lungs,  so  that  the 
latter  expand  along  with  the  chest  cavity,  the  whole  constitut- 
ing the  act  of  inspiration,  or  breathing  in.  When  the  dia- 
phragm and  the  intercostal  muscles  relax,  the  elasticity  of  the 


CIRCULATION,   RESPIRATION  AND   EXCRETION       135 

chest  walls  causes  them  to  return  to  their  original  position  and 
this,  together  with  the  elasticity  of  the  lung  tissue  itself,  com- 
presses the  air  in  the  alveoli  and  forces  part  of  it  out  through 
the  trachea,  this  constituting  the  movement  of  expiration. 

Inspiration  is  an  active  process,  while  expiration  is  chiefly 
passive.  The  respiratory  movements  are  ordinarily  what  are 
called  involuntary,  i.e.,  they  go  on  independent  of  conscious- 
ness, being  governed  by  automatic  nerve  impulses,  conveyed 
by  nerves  of  various  origin  but  controlled  by  the  so-called  "  res- 
piratory center,"  although  the  movements  can  be  accelerated 
or  retarded  or  even  suspended  entirely  for  a  few  moments  by 
an  effort  of  the  will. 

From  the  foregoing,  it  is  plain  that  the  ventilation  of  the 
lungs  does  not  consist  in  the  passage  of  air  through  them  but  of 
a  surging  or  tidal  movement  in  and  out.  The  alveoli  are  never 
entirely  emptied  of  air  even  in  forced  expiration.  In  inspiration 
the  new  or  tidal  air  enters  the  trachea  and  bronchi,  gives  up  by 
diffusion  some  of  its  oxygen  to  the  residual  air  in  the  alveoli 
and  receives  from  the  latter  some  of  the  carbon  dioxid  which 
it  contains.  In  this  way,  by  the  ebb  and  flow  of  the  tidal  air 
and  by  diffusion  between  it  and  the  residual  air,  fresh  oxygen 
is  being  continually  introduced  into  the  lungs  and  carbon 
dioxid  continually  removed. 

191.  Absorption  of  oxygen.  —  The  oxygen  introduced  into 
the  alveoli  of  the  lungs  in  the  manner  just  described  is  still 
outside  the  body  proper,  just  as  is  the  feed  in  the  digestive 
tract.  In  order  to  fulfill  its  functions  it,  like  the  feed,  must  be 
transmitted  to  the  blood  for  distribution  to  the  tissues.  This 
transfer  is  accomplished  in  the  lung  capillaries  as  is  that  of  the 
feed  in  the  intestinal  capillaries.  In  the  lung  capillaries  the 
blood  is  separated  from  the  air  of  the  alveoli  only  by  a  thin  mem- 
brane. The  coloring  matter  of  the  red  corpuscles,  haemoglobin, 
has  the  power  of  entering  into  combination  with  oxygen,  of 
which  it  can  take  up  a  maximum  of  about  1.66  c.c.  per  gram, 
forming  a  loose  chemical  compound  known  as  oxy haemoglobin. 
The  red  corpuscles  of  the  venous  blood  as  it  comes  to  the  lungs 
contain  chiefly  haemoglobin.  In  their  passage  through  the 
lung  capillaries  they  are  exposed  to  the  oxygen  of  the  alveolar 
air  and,  aided  by  the  relatively  large  surface  of  the  blood  cor- 
puscles, their  haemoglobin  takes  up  more  or  less  oxygen  and  is 


136  NUTRITION  OF  FARM  ANIMALS 

converted  partly  or  wholly  into  oxy haemoglobin,  the  amount 
of  the  oxygen  taken  up  ranging  from  eight  to  twelve  volume 
per  cent.  The  color  of  haemoglobin  is  a  dark  red  or  purplish, 
while  that  of  oxyhagmoglobin  is  bright  scarlet.  To  this  differ- 
ence of  color  is  due  the  marked  difference  in  appearance  be- 
tween venous  and  arterial  blood. 

192.  Respiration  of  tissues.  —  The  term  respiration  is  very 
commonly  applied  to  the  mechanical  processes  of  breathing 
just  described  or  to  the  exchange  of  gases  in  the  lungs.  In 
reality  all  these  are  preliminary  to  the  real  respiration,  which 
takes  place  in  the  tissues.  The  vital  processes  in  the  body 
cells  consist,  broadly  speaking,  as  will  appear  in  detail  in  the 
next  chapter,  of  a  series  of  oxidations.  The  requisite  oxygen 
is  necessarily  drawn  from  the  lymph  in  which  the  cells  exist  (185), 
while  the  carbon  dioxid  produced  by  oxidation  is  discharged 
into  it.  The  lymph,  therefore,  tends  continually  to  become 
richer  in  carbon  dioxid  and  poorer  in  oxygen.  In  the  manner 
just  described  the  blood  takes  up  oxygen  in  the  lungs  and  acts 
as  a  carrier  through  the  body.  Through  the  capillary  blood 
vessels  of  the  body  generally,  therefore,  there  are  continually 
passing  red  blood  corpuscles  charged  with  loosely  combined 
oxygen,  while  on  the  other  side  of  the  capillary  wall  is  a  fluid 
(the  lymph)  in  which  the  partial  pressure  of  oxygen  is  relatively 
low.  Accordingly,  the  combination  of  oxygen  and  haemoglo- 
bin is  dissociated  to  a  greater  or  less  extent  and  oxygen  passes 
into  the  lymph  as  required  to  supply  the  needs  of  the  cells.  At 
the  same  time  the  excess  of  carbon  dioxid  in  the  lymph  passes 
in  the  opposite  direction  into  the  blood  and  is  thus  removed 
from  the  neighborhood  of  the  cell.1  It  is  this  continual  con- 
sumption of  oxygen  and  elimination  of  carbon  dioxid  by  the 
cells  which  constitutes  the  real  act  of  respiration,  while  the 
complex  structure  of  the  lungs  and  the  elaborate  mechanism  of 
breathing  and  of  the  blood  corpuscles  are  simply  means  for 
providing  oxygen  to  the  cells  and  taking  away  carbon  dioxid. 
That  the  movements  of  breathing  are  not  an  essential  part  of 
respiration  is  strikingly  shown  by  the  fact  that  it  is  perfectly 
possible  by  suitable  devices  to  maintain  oxygenation  of  the  blood 

1  In  these  exchanges,  as  in  other  similar  ones,  while  diffusion  doubtless  plays  a 
large  part,  its  effects  are  no  doubt  modified  by  the  special  properties  of  the  living 
cells. 


CIRCULATION,   RESPIRATION  AND   EXCRETION       137 

of  an  animal  in  the  absence  of  any  respiratory  movements  what- 
ever. 

193.  Respiration  regulated  by  cell  activity.  —  It  is  apparent 
from  the  foregoing  that  the  amount  of  oxygen  taken  up  by  the 
blood  in  the  lungs  depends  in  the  first  instance  upon  the  amount 
of  this  element  consumed  by  the  body  cells.     When  they  are 
relatively  inactive  they  take  up  correspondingly  little  oxygen 
from  the  lymph  and  the  tension  of  oxygen  in  the  latter  is  low- 
ered but  little.     As  a  consequence  there  is  less  dissociation  of 
the  oxyhaemoglobin  in  the  blood  and  the  corpuscles  tend  to 
return  to  the  lungs  still  carrying  more  or  less  oxygen  and  there- 
fore capable  of  taking  up  relatively  less.     On  the  other  hand,  as 
the  tissues  become  more  active  they  consume  more  oxygen,  the 
oxyhaemoglobin  in  the  corpuscles  is  more  extensively  dissociated 
and  the  corpuscles  tend  to  come  back  to  the  lungs  relatively 
exhausted  of  oxygen  and  ready  to  take  up  the  maximum  amount. 

Any  considerable  degree  of  tissue  activity,  however,  calls  for 
a  more  rapid  supply  of  oxygen  than  can  be  provided  for  in  this 
way  and  this  need  is  met  by  a  nerve  stimulus  to  the  heart,  caus- 
ing it  to  beat  faster  and  more  powerfully,  thus  increasing  the 
arterial  pressure  and  therefore  the  amount  of  blood  passing 
through  the  capillaries  in  a  given  time.  In  these  two  ways 
the  amount  of  oxygen  absorbed  in  the  lungs  is  very  accurately 
adjusted  to  the  needs  of  the  organism.  It  is  impossible  to 
stimulate  the  body  oxidations  by  a  free  supply  of  air  as,  for 
example,  by  deep  and  rapid  breathing,  as  one  might  blow  up  a 
fire  with  a  bellows,  or  to  get  more  intense  combustion  by  re- 
placing air  with  pure  oxygen.  In  the  body  such  additional  air 
or  oxygen  never  reaches  the  fire.  Each  corpuscle  is  a  recep- 
tacle which  can  carry  only  a  definite  amount  of  oxygen  and  if 
it  comes  back  to  the  source  still  partly  filled  it  takes  up  so  much 
the  less  on  its  next  trip,  or  if  it  travels  slowly  it  is  less  efficient 
than  if  it  returns  more  frequently.  The  respiration  of  the 
tissues  can  no  more  be  affected  by  increasing  the  ventilation  of 
the  lungs  than  the  amount  of  water  delivered  by  a  pump  is  by 
the  volume  of  the  stream  from  which  the  water  is  taken. 

194.  Regulation  of  the  rhythm  of  breathing.  —  The  illus- 
tration just  used  is  true,  of  course,  only  on  the  condition  that 
the  stream  carries  at  least  as  much  water  as  the  pump  can 
handle.     So,  too,  the  amount  of  oxygen  available  in  the  lungs 


138  NUTRITION  OF  FARM   ANIMALS 

must  at  least  equal  the  amount  required  by  the  tissues.  It  is 
a  familiar  observation  that  the  rate  of  ventilation  of  the  lungs 
varies  with  the  varying  activity  of  the  body  cells.  This  is 
true  of  all  these  activities,  but  is  most  familiar  in  the  case  of 
muscular  work  which,  as  everyone  knows,  promptly  increases 
the  rate  and  depth  of  breathing,  so  that  severe  exercise,  such  as 
rapid  running,  for  example,  brings  into  play  all  the  reserve  re- 
sources of  the  breathing  mechanism.  As  already  stated 
(190),  the  muscles  which  are  used  in  breathing  are  ordinarily 
controlled  from  the  so-called  "  respiratory  center  "  and  it  is 
through  this  center  that  the  regulation  is  effected.  If,  for 
example,  an  animal  be  supplied  with  air  largely  diluted  with 
some  indifferent  gas,  such  as  nitrogen  or  hydrogen,  the  partial 
pressure  of  the  oxygen  in  the  alveoli  is  so  reduced  that  the  hae- 
moglobin of  the  blood  is  only  partially  saturated  with  oxygen. 
Such  a  deficiency  of  oxygen  stimulates  the  respiratory  center 
and  produces  more  active  breathing  and  a  corresponding  in- 
crease in  the  rapidity  with  which  the  air  in  the  alveoli  (residual 
air)  is  renewed. 

Under  ordinary  conditions,  however,  the  stimulus  to  the 
respiratory  center  is  not  a  lack  of  oxygen  in  the  blood  but  an 
excess  of  carbon  dioxid.  As  has  already  been  implied,  the 
lungs  serve  not  only  for  the  absorption  of  oxygen  but  for  the 
elimination  of  the  carbon  dioxid  produced  by  respiration, 
which  passes  by  way  of  the  lymph  to  the  blood  and  thence  to 
the  air  in  the  alveoli  of  the  lungs.  Any  increase  in  the  ac- 
tivity of  the  tissues  by  which  more  carbon  dioxid  is  produced 
tends  to  increase  the  content  of  this  substance  in  the  blood. 
Even  a  very  slight  increase,  however,  promptly  stimulates  the 
respiratory  center  and  so  causes  greater  activity  of  the  muscles 
concerned,  resulting  especially  in  deeper  and  to  some  extent  more 
rapid  breathing.  By  this  means  the  ventilation  of  the  lungs 
is  augmented  and  so  provision  is  made  for  the  removal  of  a 
greater  amount  of  carbon  dioxid. 

It  is  plain,  however,  that  a  simple  increase  in  the  lung  ven- 
tilation alone  is  not  sufficient,  except  in  a  limited  degree,  to  carry 
away  more  carbon  dioxid  from  the  tissues.  Along  with  the 
increased  ventilation  there  must  be  an  increase  in  the  rapidity 
of  the  blood  current  which  is  the  medium  by  which  the  transfer  of 
gases  between  the  lungs  and  the  lymph  takes  place.  Accordingly, 


CIRCULATION,   RESPIRATION  AND   EXCRETION       139 

we  find  that  substantially  the  same  stimuli  which  cause  more 
active  breathing  also  stimulate  the  heart  action  and  vice  versa. 
Lack  of  oxygen  or  excess  of  carbon  dioxid  are  the  two  prin- 
cipal factors  in  regulating  the  breathing  rhythm  but  by  no  means 
the  only  ones.  They  are,  however,  the  ones  of  most  impor- 
tance in  the  present  connection. 

195.  Gaseous  exchange  through  the  skin.  —  In  addition  to 
the  exchange  of  gases  between  the  air  and  the  blood  which 
goes  on  in  the  lungs,  a  similar  process  takes  place,  though  to  a 
much  smaller  extent,  through  the  skin.     The  true  skin,  under- 
lying the  cuticle  or  scarf-skin,  is  penetrated  by  capillary  blood 
vessels,  and  in  its  passage  through  these  capillaries  the  blood 
gives  off  some  carbon  dioxid  and  takes  up  some  oxygen  by  dif- 
fusion through  the  skin.     The  amounts  given  off  and  taken 
up  are  small  compared  with  the  corresponding  amounts  in  the 
lungs,  but  still  are  not  inconsiderable,  and  must  be  taken  into 
account  in  accurate  experimental  work. 

§  3.  EXCRETION 

196.  Excretory   products.  —  As   already   implied,   the  vital 
activities  of  the  body  cells  lead  to  the  formation  of  products 
which  must  be  removed  from  the  cells  and  some  of  which  must 
ultimately  be  discharged  from  the  body.     The  next  chapter 
will  be  concerned  with  the  nature  of   the  more  important   of 
these  products  and  with  some  of  the  steps  by  which  they  are 
formed.     For  the  present,  it  suffices  to  say  that  the  gradual 
oxidations  of  non-nitrogenous  material  taking  place  in  the  cells 
give  rise  substantially  to  the  production  of  carbon  dioxid  and 
water,  while  the  proteins  and  related  substances  yield  in  addition 
certain  comparatively  simple  nitrogenous  substances  of  which 
the  most  abundant  is  urea.     In  addition  to  these  substances, 
more  or  less  of  the  mineral  ingredients  also  pass  into  the  excreta. 

197.  Excretion  of  carbon  dioxid.  —  As  stated  in  the  previous 
section,  the  carbon  dioxid  produced  by  the  tissue  respiration 
passes  by  way  of  the  lymph  into  the  blood  and  is  excreted 
through  the  lungs  and  to  a  minor  degree  through  the  skin.     In 
the  blood  the  carbon  dioxid  is  carried  by  both  the  corpuscles 
and  the  plasma,  but  chiefly  (two-thirds  or  more)  by  the  latter, 
in  combination  with  proteins  and  haemoglobins,  but  especially 


140  NUTRITION  OF  FARM  ANIMALS 

with  the  alkalies.  As  in  the  case  of  oxygen,  the  amount  of 
carbon  dioxid  contained  in  the  blood  depends  upon  the  partial 
pressure  of  this  gas  in  the  surrounding  medium.  Since  the  ten- 
sion of  the  carbon  dioxid  in  the  alveolar  air  is  less  than  that  in 
the  blood  of  the  alveolar  capillaries,  the  carbon  dioxid  passes 
from  the  latter  to  the  former.  If  the  air  were  stationary  the 
process  would  continue  until  an  equilibrium  was  reached. 
Since  the  air  is  being  continually  renewed  by  breathing,  the 
tension  of  carbon  dioxid  in  it  is  kept  permanently  lower  than 
that  in  the  blood  and  there  is,  therefore,  a  continual  passage  of 
carbon  dioxid  from  the  blood  to  the  alveolar  air. 

It  is  by  means  of  this  tendency  to  equilibrium  that  the  mech- 
anism for  the  regulation  of  breathing  is  set  in  motion.  In- 
creased tissue  respiration  discharges  more  carbon  dioxid  into  the 
blood,  where  its  tension  increases.  This  causes  a  more  rapid 
diffusion  of  the  gas  into  the  alveolar  air  and  tends  to  raise  its 
carbon  dioxid  tension  also,  so  that  with  an  unchanged  rate  of 
lung  ventilation  the  carbon  dioxid  level  of  both  the  alveolar 
air  and  the  blood  would  be  raised.  Even  a  very  slight  rise  in 
the  carbon  dioxid  tension  in  the  blood,  however,  as  already 
stated,  acts  promptly  upon  the  respiratory  center  and  stimu- 
lates the  muscles  of  breathing,  resulting  in  an  increased  lung 
ventilation  and  consequently  a  more  rapid  excretion.  At  the 
same -time  the  rapidity  of  circulation  is  increased  and  in  these 
two  ways  the  level  of  carbon  dioxid  tension  in  the  blood  and 
in  the  alveolar  air  is  maintained  very  constant.  On  the  other 
hand,  if  the  lung  ventilation  be  artificially  increased,  as  by 
artificial  respiration  or  by  the  use  of  oxygen,  the  carbon  dioxid 
excretion  may  be  so  facilitated  that  the  amount  in  the  blood 
falls  below  the  normal  and  the  movements  of  breathing  may  be 
temporarily  suspended  (apncea). 

198.  Excretion  of  nitrogenous  products.  —  The  urea  and 
other  nitrogenous  products  of  cell  action,  like  the  non-nitrog- 
enous products,  pass  ultimately  into  the  blood.  In  its  course 
through  the  body  the  blood  passes  through  a  capillary  system 
in  two  bean-shaped  organs,  the  kidneys,  indicated  by  t  in  Fig. 
1 8,  situated  in  the  abdominal  cavity  on  either  side  of  the  spine 
near  the  loins.  In  these  organs  the  urine  is  being  continually 
secreted,  passing  thence  through  the  ureters  into  the  bladder 
from  whence  it  is  voided  at  intervals. 


CIRCULATION,   RESPIRATION  AND   EXCRETION        141 

The  chief  stimulus  to  the  secretion  of  water  by  the  kidneys 
is  the  water  content  of  the  blood,  the  kidneys  acting  as  regu- 
lators of  this  important  factor  and  eliminating  more  or  less  water 
as  the  blood  contains  a  larger  or  smaller  percentage  of  it. 

As  regards  the  excretion  of  dissolved  matter,  very  interesting 
relations  exist.  With  one  important  exception  (hippuric  acid) 
the  kidneys  do  not  manufacture  the  excretory  products.  Their 
essential  function  is  to  maintain  the  composition  of  the  blood 
constant.  For  each  substance  capable  of  being  excreted  at  all 
in  the  urine  there  exists  a  certain  minimum  concentration  in 
the  blood  above  which  it  begins  to  pass  through  the  kidneys  into 
the  urine.  For  the  normal  excretory  products,  as  well  as  for 
foreign  substances,  this  minimum  approaches  zero,  that  is,  only 
very  minute  amounts  of  these  substances  can  be  retained  in 
the  blood.  For  dextrose  the  limit  is  approximately  0-2-0-3 
per  cent,  for  sodium  chlorid  0-6  per  cent,  etc.  So  long  as 
the  percentage  of  one  of  these  substances  in  the  blood  does  not 
exceed  its  own  particular  limit,  none  of  it  is  excreted  through  the 
kidneys.  On  the  other  hand,  &  slight  rise  above  this  limit 
causes  an  excretion  of  the  substance  concerned.  This  function 
of  the  kidneys  has  been  likened  to  the  working  of  an  overflow 
valve  on  a  tank.  It  should  be  added  that  each  particular  sub- 
stance has  its  own  minimum,  independent  to  a  large  degree  of 
all  the  others. 

The  functions  of  the  kidneys,  however,  in  this  respect  are 
not  so  simple  as  those  of  an  overflow  valve  for  the  reason  that 
the  concentration  of  the  excreted  substances  is  greater  in  the 
urine  than  in  the  blood.  In  other  words,  the  kidney  does  its 
work  by  transferring  substances  from  a  fluid  of  lower  to  a  fluid 
of  higher  osmotic  pressure  and  the  expenditure  of  energy  in 
this  work  is  not  inconsiderable.  This  is  notably  true  o£  urea 
and  the  other  nitrogenous  waste  products,  of  which  only  traces 
can  be  detected  in  the  blood. 

In  addition  to  the  nitrogenous  substances  excreted  in  the 
urine  there  are  present  in  the  feces,  as  already  noted  (154), 
excretory  products  which  represent  a  certain  fraction  of  the 
organic  body  waste.  Finally,  small  amounts  of  urea  and 
other  nitrogenous  substances  are  excreted  in  the  perspiration. 

199.  Excretion  of  ash  ingredients.  —  Being  non-volatile 
the  ash  ingredients  are  excreted  chiefly  through  the  feces  or 


142  NUTRITION  OF  FARM  ANIMALS 

urine  according  as  the  intestines  or  kidneys  form  the  normal 
path  of  excretion,  although  they  are  contained  to  a  small  ex- 
tent also  in  the  perspiration. 

The  intestines  are  the  usual  path  of  excretion  for  certain 
mineral  substances,  notably  iron,  calcium  and  to  some  extent 
magnesium.  To  these  must  be  added  in  the  case  of  the  her- 
bivora  phosphoric  acid,  which,  under  ordinary  conditions,  is 
excreted  in  the  feces.  The  urine  of  herbivora,  especially  when 
they  consume  roughage  freely,  or  in  more  general  terms  when 
the  basic  predominate  over  the  acid  ingredients  of  the  ash,  is 
alkaline  and  contains  but  minute  amounts  of  phosphoric  acid. 
On  the  other  hand,  during  fasting  or  upon  a  ration  having  an 
acid  ash,  the  urine  may  have  an  acid  reaction  and  then,  like  the 
acid  urine  of  carnivora  or  omnivora,  may  contain  phosphoric 
acid.  The  urine  is  the  normal  vehicle  for  the  excretion  of 
sulphur,  chlorin  and  the  alkalies. 

200.  Excretion  of  water.  —  The  motions  of  air  in  and  out  of 
the  lungs  are  the  means  of  removing  from  the  body  more  or 
less  incidentally  large  amounts  of  water  by  simple  evapora- 
tion. The  presence  of  water  vapor  in  the  expired  air  is  a  fa- 
miliar fact,  shown  by  its  condensation  on  a  cold  surface  or  in 
cold  air.  The  skin  likewise  acts,  by  means  of  its  sweat-glands, 
as  a  channel  for  the  removal  of  water  from  the  system,  con- 
siderable being  continually  evaporating  from  the  skin  in  the 
form  of  the  "  insensible  perspiration."  Under  certain  circum- 
stances the  excretion  of  water  is  so  rapid  as  to  give  rise  to  the 
formation  of  visible  drops  (sweating). 

The  amounts  of  water  excreted  in  these  two  ways  are  larger 
than  are  sometimes  realized.  For  example,  a  thousand  pound 
ox  at  ordinary  temperature  and  on  light  feed  may  easily  ex- 
crete through  the  lungs  and  skin  eight  to  ten  pounds  of  water 
in  twenty-four  hours,  the  amount  depending  to  a  considerable 
extent  upon  the  temperature  and  amount  of  movement  of  the 
surrounding  air.  The  feces  also  contain  a  large  percentage  of 
water  and  in  the  case  of  herbivorous  animals  the  amount  thus 
eliminated  is  very  considerable. 

Finally,  water  is  excreted  in  the  urine,  serving  as  a  solvent 
for  the  nitrogenous  products  of  cell  activity  which  are  removed 
through  this  channel.  The  amount  of  water  thus  excreted  de- 
pends in  part  upon  the  amount  consumed,  in  part  upon  the 


CIRCULATION,   RESPIRATION  AND   EXCRETION        143 

quantity  of  nitrogenous  material  which  must  be  dissolved  and 
in  part  upon  the  amount  eliminated  through  the  lungs  and 
skin. 

Most  of  the  water  excreted  by  animals  is,  of  course,  con- 
sumed as  such,  but  it  includes  also  that  formed  by  the  oxida- 
tion of  organic  hydrogen  —  the  so-called  metabolic  water. 
Babcock  has  shown  that  in  some  classes  of  animals,  notably 
insects,  this  metabolic  water  suffices  for  all  the  needs  of  the 
organism,  so  that  they  are  not  dependent  upon  a  supply  of 
drinking  water. 


CHAPTER  V 
METABOLISM 

§  i.   GENERAL  CONCEPTION 

201.  Assimilation  and  excretion.  —  The  cell  has  already  been 
defined  (73)  as  the  biological  unit  of  life.     It  is  the  living  proto- 
plasm of  the  body  cells  which  is  the  seat  of  the  multifarious 
activities  of  the  organism. 

Every  such  activity  requires  an  expenditure  of  energy,  de- 
rived from  the  breaking  down  of  constituents  of  the  .proto- 
plasm itself  or  of  cell  enclosures  and  solutes  and  their  transfor- 
mation into  other  forms.  The  presence  of  oxygen  is  essential 
to  these  changes  and  while,  as  will  appear,  they  seldom  are 
primarily  direct  oxidations,  nevertheless,  they  yield  products 
which  are  ultimately  oxidized  to  carbon  dioxid,  water  and 
other  comparatively  simple  compounds. 

Two  things,  then,  are  necessary  for  the  continued  life  of  the 
cell :  first,  a  supply  of  material  from  without  to  replace  that 
consumed  and,  second,  the  removal  of  the  waste  products  of 
its  activities.  Both  conditions  are  fulfilled  in  the  higher  ani- 
mals by  the  circulation  of  the  blood  and  lymph.  In  the  pro- 
cesses of  digestion,  the  heterogeneous  nutritive  materials  con- 
tained in  the  feed  are  gradually  brought  into  solution  by  a  series 
of  molecular  cleavages,  so  that  the  resorptive  organs  transmit 
to  the  blood  and  lymph  current  a  qualitatively  uniform  material 
consisting  of  substances  of  comparatively  simple  molecular 
structure  (146,  147),  while  oxygen  is  supplied  to  the  blood  cor- 
puscles through  the  lung  capillaries.  The  mechanism  of  cir- 
culation is  continually  distributing  to  each  tissue  and  cell  oxygen 
from  the  lungs  and  nutritive  material  from  the  digestive  tract 
and  carrying  away  the  waste  products  of  cell  action  to  the 
various  organs  of  excretion  which  remove  them  from  the  body. 

202.  Definition  of  metabolism.  —  It  is  clear  from  the  fore- 
going that  the  body  is  the  seat  of  extensive  chemical  trans- 

144 


METABOLISM  145 

formations.  On  the  one  hand,  molecules  of  resorbed  digestion 
products  are  being  assimilated  by  the  body  cells  and  built  up 
into  the  structure  of  their  protoplasm,  while,  on  the  other 
hand,  molecules  of  protoplasm  or  of  cell  enclosures  are  being 
broken  down  and  oxidized,  yielding  finally  the  relatively  simple 
excretory  products. 

The  term  metabolism  is  commonly  used  to  designate  the  to- 
tality of  the  chemical  changes  which  the  constituents  of  the 
resorbed  feed  undergo  in  the  course  of  their  conversion  into 
the  corresponding  excretory  products.  Similarly,  one-  may 
speak  in  a  more  restricted  sense  of  the  metabolism  of  single 
ingredients  of  the  feed,  as  of  the  proteins,  carbohydrates  or 
fats,  protein  metabolism,  for  example,  signifying  the  chemical 
changes  undergone  by  the  digestion  products  of  the  proteins 
of  the  feed  during  their  assimilation  and  subsequent  transfor- 
mation into  excretory  products.  The  adjective  metabolic  is 
also  used  to  describe  these  chemical  changes. 

203.  Anabolism  and  katabolism.  —  The  term  metabolism, 
as  just  defined,  includes  processes  of  two  distinct  kinds,  viz., 
those  by  which  molecules  of  sugars,  organic  acids,  amino  acids, 
etc.,  are  built  up  into  more  complex  compounds  in  the  body 
and  those  by  which  these  complex  compounds  are  broken  down 
again  into  simpler  substances  and  finally  into  the  excretory 
products. 

The  building  up  metabolism  has  received  the  name  anabolism, 
while  the  breaking  down  or  oxidative  phase  is  called  katabolism. 
Any  change  in  the  direction  of  greater  molecular  complexity 
is  spoken  of  as  an  anabolic  change,  while  one  in  the  direction  of 
greater  molecular  simplicity  is  a  katabolic  change. 

It  must  not  be  inferred  from  what  has  been  said  that  anabolism 
always  precedes  katabolism.  Neither  is  the  breaking  down  of  cell 
constituents  by  any  means  a  process  of  uninterrupted  katabolism. 
On  the  contrary,  many  instances  are  known  in  which  it  is  interrupted 
at  various  stages  by  anabolic  changes  of  one  sort  or  another.  While 
the  general  direction  of  the  change  is  towards  simplification,  there 
are  eddies  in  the  current.  Moreover,  it  is  by  no  means  probable  that 
all  the  resorbed  substances  are  actually  built  up  into  protoplasm 
before  being  katabolized.  It  is  true  that,  to  trie  best  of  our  knowl- 
edge, the  metabolic  processes  take  place  within  the  cells  but  it  ap- 
pears unlikely  that  the  relatively  large  amounts  of  material  some- 
L 


146  NUTRITION  OF  FARM  ANIMALS 

times  katabolized  must  first  become  integral  parts  of  the  protoplasm. 
In  other  words,  it  is  probable  that  the  cells  have  the  power  to  katab- 
olize  substances  present  within  them  but  not  structurally  a  part  of 
them. 

204.  Synthetic  processes  in  the  body.  —  The  foregoing  conception 
of  metabolism  implies  that  the  body  has  power  to  carry  out  extensive 
chemical  syntheses,  contrary  to  the  idea  still  current  that  the  course 
of  chemical  change  in  the  organic  world  is  toward  the  building  up  of 
complex  compounds  in  the  plant  and  their  breaking  down  to  simpler 
ones  in  the  animal.     Synthethic  chemical  changes  were  long  regarded 
as  peculiar  to  the  vegetable  kingdom,  while  the  reactions  in  the  ani- 
mal body  were  supposed  to  be  exclusively  analytic.     The  first  syn- 
thetic action  to  be  recognized  in  the  animal  was  the  formation  of 
hippuric  acid  from  benzoic  acid,  discovered  by  Keller  and  Wohler  in 
1824,  and  which  attracted    wide    attention.     More    recent    physio- 
logical investigations  have  shown  that  this  is  by  no  means  an  isolated 
case,  but  that  syntheses  in  great  variety  are  executed  in  the  animal 
body.     No  such  sharp  distinction  between  animal  and  vegetable 
organisms  exists  as  was  formerly  supposed.     The  fundamental  laws 
of  metabolism  are  the  same  for  both  and  both  execute  synthetic  as 
well  as  analytic  processes.     It  is  only  the  special  synthetic  activity 
of  the  chlorophyl  in  green  plants  which  tends  to  obscure  this  funda- 
mental likeness.     The  conception,  then,  that  the  digestive  cleavages 
supply  to  the  body  cells  comparatively  simple  "building  stones" 
which  are  synthesized  to  produce  the  complex  ingredients  of  cells 
and  tissues  is  quite  in  harmony  with  our  general  knowledge  of  the 
nature  of  metabolism. 

205.  Metabolism  oxidative  and  analytic.  —  Metabolism  re- 
garded as  a  whole  may  be  characterized  chemically  as  an  oxi- 
dation.    Oxygen  is  introduced  into  the  system   through   the 
blood  and  reacts  with  the  feed  or  tissue  materials  or  with  the 
products  of  their  breaking  down,  and  the  final  excretory  products 
are  either  completely  oxidized  substances,  like  carbon  dioxid 
and   water,   or   substances    approaching    this    condition,    like 
urea,  etc. 

From  a  slightly  different  point  of  view,  metabolism  as  a  whole 
may  be  characterized  as  an  analytic  as  opposed  to  a  synthetic 
process.  The  general  tendency  is  toward  the  formation  of 
simpler  molecules.  For  example,  the  molecule  of  dextrose  or 
levulose  contains  24  atoms  and  those  of  the  three  most  com- 
mon fats,  respectively,  155,  167  and  173  atoms,  while  the 
molecules  of  carbon  dioxid  and  water  resulting  from  their  metab- 


METABOLISM  147 

olism  contain  but  3  atoms  each.  Even  the  cleavage  products 
of  protein  which  are  resorbed  from  the  digestive  tract  are,  with 
few  exceptions,  much  more  complex  than  the  final  products 
which  result  from  their  metabolism. 

206.  Metabolism  a  gradual  process.  —  While  metabolism 
has  just  been  characterized  as  an  oxidative  process,  and  is  often 
loosely  spoken  of  as  a  burning  of  the  feed  or  tissue  ingredients, 
it  is  in  fact  radically  different  from  what  is  commonly  under- 
stood by  these  terms.  The  building  up  and  breaking  down  of 
materials  in  metabolism  is  a  gradual,  i.e.,  a  step  by  step,  process. 

Metabolism  is  the  sum  of  the  chemical  reactions  through  which 
the  life  of  the  cells  is  manifested.  These  reactions,  however, 
differ  from  tissue  to  tissue  and  from  cell  to  cell,  and  even  in  the 
same  cell  from  time  to  time,  and  the  resulting  products  are 
correspondingly  numerous  and  varied.  Between  the  nutrients 
supplied  to  the  cells  by  the  blood  and  the  final  products  of 
metabolism  as  excreted  from  the  body  there  are  innumerable 
intermediate  products,  comparatively  few  of  which,  in  all  proba- 
bility, have  been  recognized.  We  know  the  first  and  last  terms 
of  the  series  and  thus  are  able  to  measure,  as  it  were,  the  alge- 
braic sum  of  the  changes,  but  of  the  single  factors  making  up 
the  so-called  intermediary  metabolism  as  well  as  of  the  specific 
tissues  concerned  in  the  changes,  we  are  largely  ignorant,  al- 
though we  know  that  they  are  numerous. 

Furthermore,  while  metabolism  results  in  the  formation  of 
highly  oxidized  products,  it  does  not  consist  primarily  in  the 
direct  union  of  oxygen  with  feed  materials,  i.e.,  the  step  by 
step  processes  of  which  it  is  made  up  do  not  consist  of  a  series 
of  partial  oxidations.  The  primary  processes  of  metabolism 
are  of  the  nature  of  cleavages  and  hydrations  and  it  is  only 
the  comparatively  simple  molecules  resulting  from  these  which 
unite  directly  with  oxygen.  Correspondingly,  the  extent  of 
metabolism  is  determined  by  the  amount  of  functional  activity 
of  the  various  cells  and  not,  as  in  the  case  of  direct  oxidation 
in  a  fire,  by  the  supply  of  oxygen  (193) .  The  somewhat  com- 
mon notion  that  an  increased  proportion  of  oxygen  in  the  air  or  a 
voluntary  increase  in  the  rate  and  depth  of  breathing  may  cause 
more  material  to  be  oxidized  in  the  body  is  without  foundation, 
except  -so  far  as  increased  breathing  involves  increased  mus- 
cular exertion. 


148  NUTRITION  OF  FARM   ANIMALS 

207.  Purpose  of  metabolism.  —  As  implied  at  the  opening 
of  this  chapter,  the  vital  activities  of  the  body  are  essentially 
transformations  of  energy.  The  living  body  is  continually 
doing  work  upon  its  surroundings  and  continually  loosing  heat 
to  them  and  the  energy  for  the  production  of  work  and  the  main- 
tenance of  the  body  temperature  is  derived,  as  already  stated, 
from  the  transformation  of  the  chemical  energy  contained  in 
the  substances  broken  down,  tiiis  transformation  being  indeed 
the  essence  of  the  whole  process.  This  fact  is  familiarly,  if  not 
altogether  accurately,  expressed  in  the  statement  that  the 
feed  is  the  fuel  of  the  body. 

There  will  be  occasion  later  to  consider  this  aspect  of  the 
matter  in  detail,  but  it  is  important  at  the  outset  to  grasp  the 
conception  that  the  final  end  and  aim  of  metabolism  is  to  sup- 
ply energy  for  the  vital  activities  and  that  the  demand  for  en- 
ergy is  the  controlling  factor  in  all  its  processes.  It  is  these 
transformations  of  energy  which,  if  not  synonymous  with  life, 
are  at  least  its  objective  manifestation. 

But  while  it  is  essential  to  hold  fast  to  this  broad  general  con- 
ception of  metabolism,  it  is  also  important  to  understand  clearly 
that  the  processes  by  which  this  end  is  reached  are  exceedingly 
complex.  A  volume  would  be  required  for  any  adequate  dis- 
cussion even  of  existing  knowledge  regarding  the  details  of  the 
metabolic  processes.  Such  a  discussion  lies  outside  the  scope 
of  the  present  work.  All  that  is  attempted  in  this  chapter  is 
to  outline  the  metabolism  of  the  principal  groups  of  feed  sub- 
stances and,  as  preliminary  to  a  subsequent  consideration  of 
their  values  as  sources  of  matter  and  energy  to  the  body,  to 
indicate  the  functions  which  they  perform  in  the  building  up 
and  maintenance  of  the  organism  and  the  support  of  its  activ- 
ities. 

§  2.  ENZYMS  AS  AGENTS  IN  METABOLISM 

Enzym  action  has  come  to  play  so  large  a  part,  even  if  a  more 
or  less  hypothetical  one,  in  the  current  conceptions  of  the  pro- 
cesses of  metabolism  that  a  brief  outline  of  the  prevailing 
views  seems  called  for. 

208.  Extracellular  enzyms.  —  The  enzyms  of  the  digestive 
tract  are  those  which  are  most  familiar  in  physiology.  As  has 
been  seen  (114),  the  digestion  of  all  three  of  the  chief  classes 


METABOLISM  149 

of  feed  ingredients  is  brought  about  largely  or  wholly  by  their 
agency  and  is  often  effected  by  different  enzyms  in  successive 
stages.  Thus  the  ptyalin  of  the  saliva  converts  starch  into 
maltose  while  the  further  conversion  of  the  latter  into  dextrose 
is  effected  by  the  maltase  of  the  intestine.  Quite  similar  are 
the  successive  actions  of  pepsin,  trypsin  and  erepsin  on  the  pro- 
teins. In  all  these  cases,  as  well  as  in  the  even  more  familiar  case 
of  the  diastase  of  germinating  seeds,  the  enzyms  act  at  a  dis- 
tance from  the  cells  which  produce  them  and  have,  therefore, 
been  called  extracellular  enzyms. 

209.  Intracellular  enzyms.  —  From  the  fact  that  the  most 
obvious  cases  of  enzym  action  were  those  in  which  the  ferment 
acted  at  a  distance  from  the  cells  producing  it,  enzyms  came  to 
be  regarded  as  substances  whose  action  belonged  in  a  different 
category  from  that  of  living  cells.  A  sharp  distinction  was 
drawn  between  unorganized  substances,  acting  substantially 
as  chemical  reagents,  and  organisms  producing  chemical  changes 
by  virtue  of  their  life.  The  action  of  the  yeast  plant  upon  sugar 
afforded  a  typical  example  of  this  distinction.  It  was  shown 
that  yeast  secreted  an  enzym  (invertase)  which  was  capable  of 
inverting  sucrose  independently  of  the  action  of  the  yeast  cell, 
while,  on  the  other  hand,  the  alcoholic  fermentation  of  mono- 
saccharids  was  held  to  be  a  vital  function  of  the  living  yeast 
cells. 

Buchner,  however,  in  1897,  showed  that  by  suitable  means 
there  could  be  extracted  from  yeast  a  substance  (zymase) 
which  fermented  the  simple  sugars  exactly  like  yeast  in  the 
absence  of  any  living  organism  whatever;  i.e.,  it  acted  as  an 
enzym.  It  became  evident,  then,  that  the  yeast  cell  ferments 
monosaccharids  not  because  it  is  alive  but  because  it  contains 
zymase.  The  only  essential  difference  between  the  yeast  fer- 
mentation and  that,  for  example,  produced  by  diastase  or  by 
the  invertase  of  yeast  is  that  the  enzym  normally  acts  within 
the  cell  which  produces  it.  Later  it  was  shown  that  what  is 
true  of  the  yeast  fermentation  is  true  also  of  the  fermentation 
caused  by  the  lactic  acid  bacillus.  It,  too,  is  due  to  an  intra- 
cellular  enzym  which  can  be  separated  from  the  cell  and  act 
independently.  Investigators  are  inclined,  therefore,  to  re- 
gard all  fermentation  as  the  work  of  enzyms,  some  of  which, 
like  the  digestive  enzyms,  are  excreted  by  the  cells  and  may 


150  NUTRITION  OF  FARM  ANIMALS 

act  at  a  considerable  distance  from  their  point  of  origin, 
while  others  normally  produce  their  effect  within  the  secret- 
ing cell. 

210.  Intracellular  enzyms  in  the  body.  —  Still  more  recently 
the  presence  of  intracellular  enzyms  in  all  parts  of  the  animal 
body  has  been  recognized.     It  has  been  shown  that  a  very 
considerable  variety  of  reactions  which  are  known  to  take  place 
in  the  body  may  also  be  brought  about  outside  the  body  by  the 
action  of  extracts  of  various  tissues  and  organs  under  conditions 
apparently  excluding  the  action  of  any  living  organisms.     Con- 
sequently, they  have  been  ascribed  to  the  action  of  enzyms 
originally  present  in  the  cells,  and  the  reactions  in  the  body 
have   been    regarded   as    due    to    these    same  enzyms.      The 
idea  of  intracellular  enzyms  has  thus  been  extended  to  account 
for  the  metabolic  activities  of  the  organism,  and  this  explana- 
tion has  been  very  generally  accepted  by  physiologists.     Accord- 
ing to  this  view,  the  body  cells  bring  about  metabolic  changes 
substantially  in  the  same  way  as  do  the  cells  of  yeast  or  of 
the  lactic  acid  bacillus,  viz.,  by  the  formation  of  appropriate 
enzyms   which   act   upon   the  substances  to  be  metabolized. 
This    phase    of    the    subject    is    a    comparatively    new    one 
and  unanimity  as  to  individual  cases  has  by  no  means  been 
reached,  but  of  the  value  of  the  general  conception  as  a  working 
hypothesis  there  can  be  little  question. 

The  word  explanation  is  used  above,  of  course,  in  a  limited 
sense.  It  is  not  known  how  the  cell  produces  enzyms,  nor  with 
any  degree  of  certainty  how  an  enzym  acts.  Nevertheless, 
this  hypothesis,  if  confirmed,  is  a  real  explanation  as  far  as  it 
goes,  in  that  it  enables  related  phenomena  to  be  grouped  to- 
gether from  a  broader  standpoint,  as  will  be  apparent  from  the 
following  paragraphs. 

211.  Enzym  reactions  reversible.  —  A  chemical  reaction  is 
said  to  be  reversible  when  it  may  progress  in  either  direction 
according  to  the  conditions.    For  example,  if  a  mixture  of  hydro- 
gen and  iodin  in  molecular  proportions  be  heated  to  448°  C. 
hydrogen  iodid  is  produced.     If,  however,  hydrogen  iodid  be 
heated  to  the  same  temperature  it  yields  hydrogen  and  iodin. 
The  reaction  between  these  two  elements,  then,  is  represented 
by  the  equation 

H2  +  I2  ^±  (HI)2 


METABOLISM  151 

At  the  temperature  of  448°  C.,  79  per  cent  of 'the  matter  exists 
as  HI  and  the  remainder  as  free  H2  and  I2 ;  the  HI  is  dissoci- 
ated at  the  same  rate  at  which  the  H2  and  I2  unite,  and  a  con- 
dition of  chemical  equilibrium  exists.  At  a  different  temper- 
ature, the  point  of  equilibrium  is  different,  but  otherwise  the 
result  is  the  same.  In  theory,  all  chemical  reactions  are  regarded 
as  reversible,  but  in  many  cases  the  reverse  action  is  so  slight  as 
to  be  incapable  of  detection  under  attainable  experimental 
conditions,  and  such  reactions  are  often  spoken  of  as  irreversible. 

In  addition  to  the  temperature,  the  position  of  the  point  of 
equilibrium  in  a  reversible  reaction  is  affected  by  the  relative 
mass  of  the  ingredients.  Thus  if,  in  the  example  just  given, 
the  iodin  be  removed  from  the  field  of  chemical  action  (as,  for 
example,  by  condensing  it  to  the  solid  form  in  a  cold  portion 
of  the  apparatus)  the  dissociation  of  the  hydrogen  iodid  will 
proceed  until  it  is  practically  complete.  On  the  other  hand, 
if  the  hydrogen  iodid  be  removed  (as  by  allowing  it  to  react 
with  calcium  carbonate)  the  reaction  may  be  pushed  to 
completion  in  the  reverse  direction.  Similarly,  an  increase  in 
the  concentration  of  one  of  the  reacting  substances  tends  to  dis- 
place the  equilibrium  in  the  opposite  direction. 

It  is  a  matter  of  much  interest  that  at  least  some  enzym 
reactions  have  been  shown  to  be  reversible.  One  of  the  best 
authenticated  cases  appears  to  be  that  of  the  action  of  lipase  on 
fats.  It  has  been  shown  by  Kastle  and  Loevenhart 1  that  this 
enzym  acts  on  ethyl  butyrate  according  to  the  equation 

C2H5  •  C4H7O2  +  H2O  ^±  C2H5OH  +  C4H8O2 

A  similar  reaction  has  also  been  shown  to  take  place  with 
monobutyrin,  the  glycerol  ester  of  butyric  acid,  which  may  be 
regarded  as  a  simple  fat,  while  it  is  at  least  very  probable  that 
the  higher  fats  are  acted  on  in  the  same  way.  Another  example 
of  reversible  enzym  reaction  is  claimed  to  be  that  of  the  con- 
version of  maltose  into  dextrose  by  the  action  of  the  ferment 
maltase,  it  appearing,  according  to  the  researches  of  Croft 
Hill,2  that  the  same  ferment  may  also  convert  dextrose  into 
maltose.  Similar,  although  less  decisive,  results  have  also  been 
reported  regarding  the  action  of  the  proteases. 

1  Amer.  Qiem.  Jour.,  24  (1900),  491. 

2  Jour.  Chem.  Soc.,  Trans.,  73  (1898),  634. 


152  NUTRITION  OF  FARM   ANIMALS 

212.  Reversibility  of  metabolic  reactions.  —  It  would  appear, 
then,  that  the  action  of  the  intracellular  enzyms  which  are  be- 
lieved to  play  such  an  important  part  in  metabolism  may  be 
synthetic  as  well  as  analytic,  and  that  the  metabolic  processes 
may  be  conceived  of  as  a  complex  of  reversible  chemical  reac- 
tions, now  accelerated  and  now  retarded  by  appropriate  en- 
zyms.1   The  idea  that  each  cell  of  the  body  thus  exists  in  a 
state  of  constantly  shifting  chemical  equilibrium,  according  as 
the  concentration  of  one  or  another  substance  in  its  domain 
changes,  is  an  attractive  one  in  its  breadth  and  comparative 
simplicity,  and  there  seems  to  be  little  doubt  that  it  contains 
elements  of  truth  and  will  prove  an  important  aid  to  research. 
As  yet,  however,  it  is  to  be  regarded  as  a  probable  hypothesis 
rather  than  as  a  fully  established  fact. 

§  3.  THE  METABOLISM  OF  THE  CARBOHYDRATES 
The  hexose  carbohydrates 

213.  Glycogenic    function    of    the    liver.  —  The    monosac- 
charids  (principally  dextrose)  produced  in  the  digestive  cleavage 
of  the  carbohydrates  are  resorbed  chiefly  or  wholly  by  the  blood 
capillaries  of  the  intestines.     These  capillaries  unite  into  the 
portal  vein  leading  to  the  liver,  where  it  subdivides  into  a 
capillary  system  in  which  the  blood  is  brought  into  intimate 
contact  with  the  cells  of  that  organ  and  from  whence  it  passes 
by  way  of  the  hepatic  vein  into  the  posterior  vena  cava,  thus 
entering  the  general  circulation  (182). 

The  proportion  of  dextrose  found  in  the  blood  of  the  general 
circulation  is  remarkably  constant,  and  if  any  considerable 
excess  be  introduced  it  is  promptly  excreted  through  the  kid- 
neys (198).  On  the  other  hand,  the  supply  of  carbohydrates 
from  the  digestive  tract  may  be  more"  or  less  intermittent  or 
fluctuating,  so  that  there  is -evidently  need  for  some  regula- 
tory mechanism  to  prevent  a  waste  of  sugar  by  excretion  in 
the  urine.  This  regulation  is  effected  chiefly  in  two  localities, 
viz.,  in  the  muscles  and  in  the  liver.  The  function  of  the  liver 

1  That  syntheses  can  be  effected  by  the  agency  of  enzyms  seems  established,  but 
that  enzym  reactions  in  general  are  reversible  is  questioned  by  good  authorities. 
For  example,  the  ferment  maltase,  acting  on  dextrose,  is  stated  to  produce  not  mal- 
tose but  isomaltose,  and  it  is  claimed  that  a  different  enzym  is  required  to  reconvert 
isomaltose  into  dextrose. 


METABOLISM  153 

in  this  respect  was  the  earliest  to  be  discovered  and  may  be 
appropriately  considered  first. 

When  dextrose  is  being  freely  resorbed  from  the  digestive 
tract,  it  undergoes  dehydration  and  polymerization  in  the  liver, 
yielding  the  polysaccharid  glycogen  (25),  which  is  stored  up 
in  the  liver  cells.  If,  on  the  other  hand,  the  resorption  of  dex- 
trose from  the  intestines  is  insufficient  to  maintain  the  supply 
in  the  blood,  glycogen  previously  formed  may  undergo  the 
reverse  process  of  hydration  and  cleavage,  giving  rise  to  a  pro- 
duction of  dextrose.  This  regulatory  activity,  discovered  by 
Claude  Bernard  in  1853,  by  which  carbohydrates  are  held  back 
or  released  according  to  the  demands  of  the  body,  is  called  the 
glycogenic  function  of  the  liver.  While  this  function  has  other 
aspects,  as  will  appear  later,  as  respects  the  digested  carbohy- 
drates the  liver  may  be  likened  to  a  storage  reservoir  by  which 
the  flow  of  a  stream  is  controlled. 

214.  Mechanism  of  regulation.  —  It  is  of  interest  to  note 
that  this  phase  of  carbohydrate  metabolism  illustrates  two  of 
the  general  conceptions  formulated  on  preceding  pages. 

First,  the  formation  of  glycogen  is  a  synthetic  reaction.  The 
comparatively  simple  molecules  of  dextrose  are  built  up  tem- 
porarily into  the  more  complex  molecules  of  the  polysaccharid. 
In  other  words,  almost  the  first  step  in  carbohydrate  metabolism 
is  an  anabolic  change  (203). 

Second,  the  process  of  the  formation  and  destruction  of  gly- 
cogen is  susceptible  of  explanation  as  a  reversible  enzym  re- 
action (212).  It  is  known  that  the  conversion  of  glycogen  into 
dextrose  is  effected  by  an  enzym  or  enzyms  which  may  be  ex- 
tracted from  the  liver  and  which,  it  would  seem,  must  be  similar 
to  those  of  the  digestive  tract.  The  action  of  one  of  the  latter, 
maltase,  however,  is  claimed  to  be  reversible  (211),  and  one  is 
naturally  tempted  to  infer  that  the  synthesis  of  the  liver  gly- 
cogen is  effected  by  the  same  enzym  which  brings  about  its  cleav- 
age, although  experimental  proof  that  such  is  the  case  is  lacking. 
According  to  this  hypothesis,  the  changes  taking  place  in  the 
liver  would  be  represented  by  the  equation 

»(C6H1206)  $  C6nH10w05n  +  n(H20) 

An  excess  of  dextrose  in  the  blood  would  have  the  effect  of 
displacing  the  point  of  equilibrium  in  the  direction  of  the  for- 


154  NUTRITION  OF  FARM  ANIMALS 

mation  of  glycogen,  while  a  deficiency  of  dextrose  would  have  the 
contrary  effect.  If  it  be  supposed  further  that  the  glycogen 
as  soon  as  formed  combines  with  the  protoplasm  of  the  liver 
cells,  forming  compounds  which  withdraw  a  considerable  por- 
tion of  it  from  the  sphere  of  action  of  the  enzym,  after  the  anal- 
ogy of  the  precipitation  of  an  insoluble  compound,  we  have  a 
plausible,  even  if  chiefly  hypothetical,  scheme  of  the  chemical 
mechanism  of  the  process.  Whether  or  not  it  adequately  rep- 
resents the  actual  facts,  it  may  at  least  serve  as  a  concrete  il- 
lustration of  the  manner  in  which  the  conception  of  enzym  ac- 
tion may  be  applied  to  metabolic  processes. 

215.  Muscle  glycogen.  —  While  the  glycogenic  function  of 
the  liver  has  been  the  subject  of  very  extensive  investigation, 
the  presence  of  glycogen  is  by  no  means  confined  to  this  organ. 
Indeed,  glycogen  seems  to  be  a  normal  constituent  of  animal 
protoplasm.  It  is  found  in  greater  or  less  amounts  in  practi- 
cally all  tissues,  being  particularly  abundant  where  rapid  cell 
multiplication  is  taking  place,  as  in  embryonic  tissues  or  in 
rapidly  growing  tumors.  It  is  estimated  that  in  an  animal  in 
normal  condition  roughly  one-half  of  the  glycogen  of  the  body 
is  contained  in  the  liver.  Of  the  other  half  by  far  the  larger 
proportion  is  found  in  the  muscles  (96). 

The  glycogen  of  the  muscles  (and  other  organs)  is  not  simply 
glycogen  which  has  been  formed  in  the  liver  and  transported  to 
the  muscles,  but  is  produced  independently  from  the  dextrose 
of  the  blood,  apparently  in  much  the  same  manner  as  in  the 
liver.  That  this  is  true  is  shown  by  the  fact  that  glycogen  is 
still  formed  in  the  muscles  when,  by  surgical  interference 
(Eck  fistula),  the  blood  is  prevented  from  passing  through  the 
liver.  In  fact,  the  formation  of  glycogen  in  the  muscles,  etc., 
appears  to  be  the  primary  process,  while  the  liver  serves  rather 
as  a  secondary  reservoir  which  may  be  eliminated  without 
seriously  affecting  the  general  carbohydrate  metabolism.  With 
the  liver  excluded  from  the  circulation,  the  dextrose  resorbed 
from  the  digestive  tract  is  still  converted  into  glycogen  and  the 
animal  is  still  able  to  digest  considerable  quantities  of  carbohy- 
drates without  the  appearance  of  sugar  in  the  urine. 

Even  in  the  normal  animal,  however,  the  power  to  dispose  of  sur- 
plus sugar  is  not  unlimited.  If  large  quantities  of  sugar  are  consumed, 
the  conversion  into  glycogen,  together  with  the  normal  katabolism, 


METABOLISM  155 

may  not  keep  pace  with  the  resorption  and  there  occurs  an  excretion 
of  sugar  in  the  urine  —  the  so-called  "alimentary  glycosuria."  The 
amount  of  sugar  which  can  be  resorbed  without  producing  alimentary 
glycosuria,  —  i.e.,  the  limit  of  tolerance  for  sugar  —  varies  with  the 
kind  of  sugar,  being  highest  with  dextrose  (220). 

216.  Carbohydrates  formed  in  the  body.  - —  In  their  relation 
to  the  carbohydrates  of  the  feed,  the  muscles  and  liver  act,  as 
has  been  seen,  as  a  sort  of  storage  reservoir  or  regulator  of  the 
sugar  supply  to  the  blood.     The  total  withdrawal  of  carbohy- 
drates from  the  feed,  however,  by  no  means  results  in  the 
disappearance  of  these  substances  from  the  body.     The  car- 
bohydrates appear  to  be  essential  to  the  normal  course  of  metab- 
olism and  if  they  are  absent  from  the  feed,  they  are  manufac- 
tured in  the  body  from  other  materials.     A  carnivorous  animal, 
e.g.,  fed  exclusively  on  meat  or  fat,  shows  a  normal  percentage 
of  dextrose  in  its  blood,  while  its  liver  and  muscles  contain  a 
normal  amount  of  glycogen.     It  is  true  that  in  such  an  experi- 
ment small  quantities  of  glycogen  are  contained  in  the  meat 
consumed,  but   their  amount  is  entirely  insignificant  as  com- 
pared with  the  quantities  of  dextrose  which  there  is  reason  to 
believe  are  produced  and  katabolized  in  the  organism.     This 
dextrose  must  obviously  have  its  origin  either  in  the  proteins  or 
the  fats.     Which  of  the  two  is  the  source  or  whether  both  can 
be  thus  utilized  will  be  considered  later  in  connection  with 
the  metabolism  of  those  substances  (235,  253). 

217.  Formation   of   fat.  —  The   mutual    transformations   of 
sugar  and  glycogen  tend  to  keep  the  dextrose  content  of   the 
blood  approximately  constant,  while  holding  a  supply  of  readily 
available  carbohydrate  material  at  hand  to  meet  promptly  any 
sudden  demand.     The  amount  of  carbohydrates  which  can  be 
disposed  of  in  this  way  is,  however,  limited.     For  man  it  is 
estimated  at  about  300  grams  and  for  cattle  at  about  2  kilo- 
grams (96) .     It  is  evident,  then,  that  if  the  feed  contains  a  per- 
manent excess  of  carbohydrates  over  the  needs  of  the  body  the 
capacity  to  store  them  up  as  glycogen  will  soon  be  exhausted. 
A  surplus  of  carbohydrates  over  the  amount  which  can  be  dis- 
posed of  in  this  way  is  applied  by  the  organism  to  the  pro- 
duction of  fat,  which  may  be  stored  up  in  very  large  amounts 
in  the  cells  of  connective  tissue  through  the  body,  but  especially 
in  those  immediately  beneath  the  skin  and  about  the  abdominal 


156  NUTRITION  OF  FARM  ANIMALS 

organs,  constituting  the  adipose  tissue  (94).  This  tissue  con- 
stitutes a  reserve  of  non-nitrogenous  material  which  may  be 
mobilized  later  if  need  arises. 

Of  the  chemistry  of  the  conversion  of  carbohydrates  into 
fats,  as  well  as  of  the  organ  or  organs  where  it  is  effected, 
our  knowledge  is  still  meager,  but  the  fact  of  such  a  change 
is  undisputed  and  it  is  perhaps  the  most  notable  example 
of  a  synthetic  and  anabolic  process  in  the  animal  body. 
The  physiological  evidence  for  this  fact  and  the  quantitative 
relations  of  the  process  may  be  taken  up  more  conveniently 
later  (249). 

218.  Katabolism  of  carbohydrates.  —  The  physiological  sig- 
nificance of  the  dextrose  of  the  blood  and  the  glycogen  of  the 
muscles  and  liver  appears  most  clearly  when  they  are  regarded, 
not  in  the  light  of  a  more  or  less  temporary  storage  of  matter 
in  the  body,  but  rather  as  carriers  of  energy  for  the  physiological 
processes.  Of  these  processes,  the  most  obvious  one,  which 
vastly  predominates  over  all  others,  is  the  performance  of  work 
by  the  muscles,  external  and  internal,  but  what  is  true  of  mus- 
cular work  is  in  the  main  true  also  of  the  subordinate  forms  of 
glandular  and  cellular  activity.  The  former,  therefore,  may 
be  taken  as  typical. 

In  the  performance  of  muscular  work,  as  will  appear  later, 
there  is  a  rapid  katabolism  of  non-nitrogenous  material  and 
especially  of  carbohydrates,  largely,  it  would  appear,  in  the  form 
of  dextrose.  The  resulting  impoverishment  of  the  blood  in 
dextrose  causes  a  conversion  of  stored  up  glycogen  into  dextrose 
to  supply  the  lack.  If  the  view  of  the  formation  of  glycogen 
which  regards  it  as  a  reversible  reaction  may  be  accepted,  we 
may  say  that  the  chemical  equilibrium  between  the  dextrose 
and  the  glycogen  is  disturbed  by  the  removal  of  the  former 
during  muscular  work.  As  long  as  the  work  is  continued,  the 
process  of  conversion  of  glycogen  into  dextrose  also  continues, 
and  by  prolonged  work  it  is  possible  to  reduce  the  glycogen  con- 
tent of  an  animal  to  a  very  low  limit. 

It  should  be  clearly  understood  that  the  foregoing  is  only  a 
highly  schematic  view  of  the  chemistry  of  muscular  contraction 
as  related  to  the  katabolism  of  the  carbohydrates.  Some  further 
consideration  is  given  in  Chapter  XIV  (630)  to  the  very  com- 
plicated chemical  mechanism  of  the  process. 


METABOLISM  157 

219.  Intermediary  katabolism.  —  Regarding  the  intermediary 
katabolism  of  the  carbohydrates,  not  very  much  is  known. 
It  appears  probable,  however,  that  dextrose  undergoes  pre- 
liminary cleavage  with  the  formation  of  glyceric  aldehyde, 
pyruvic  aldehyde  (methyl  glyoxal)  and  either  lactic  or  pyruvic 
acid,  which  is  then  further  oxidized  to  acetic  acid,  carbon  dioxid 
and  water.  Many  facts,  including  especially  those  derived 
from  a  study  of  the  fermentation  of  sugar,  seem  to  point  to  the 
possibility  of  such  reactions.  Lactic  acid  is  also  widely  dis- 
tributed in  the  body,  although  its  presence  is  also  susceptible 
of  explanation  as  arising  in  the  katabolism  of  protein  (233), 
and,  moreover,  it  has  been  shown  that  lactic  acid  may  give  rise 
to  glycogen  or  dextrose  in  the  animal  body.  Accordingly, 
these  changes,  like  the  mutual  transformations  of  glycogen  and 
dextrose,  may  be  conceived  of  as  constituting  a  series  of  re- 
versible reactions. 

(Dextrose) 

Glycogen  ;£  CH2OH(CHOH)4CHO 

(Glyceric  aldehyde) 

CH2OH(CHOH)4CHO  ^  2CH2OH  -  CHOH  •  CHO 

(Pyruvic  aldehyde) 

CH2OH  -  CHOH  -  CHO-H2O  ^  CH3  •  CO  •  CHO 

(Lactic  acid) 

CH3  •  CO  •  CHO  +  H2O  :£  CH3CHOH  •  COOH 

or 

(Pyruvic  acid) 

CH  -  CO  •  CHO  •  +  O  ;£  CH3CO  -  COOH 

The  conversion  of  dextrose  into  lactic  acid  is  a  nearly  iso- 
thermic  process,  the  resulting  lactic  acid  containing  almost  the 
same  amount  of  chemical  energy  as  the  dextrose.  If,  then, 
these  cleavages  occur  in  the  katabolism  of  carbohydrates  they  are 
obviously  preparatory  to  the  actual  oxidation  in  which  the 
principal  portion  of  the  energy  is  liberated. 

The  pentose  carbohydrates 

The  foregoing  paragraphs  have  treated  of  the  metabolism  of 
the  hexoses,  which  constitute  the  chief  carbohydrate  supply  of 
man,  and  of  the  carnivora  so  far  as  the  latter  consume  carbo- 
hydrates. The  feed  of  herbivora,  however,  contains  also  consid- 
erable amounts  of  various  pentose  carbohydrates  which  are  in  part 


158  NUTRITION  OF  FARM  ANIMALS 

digestible,  or  at  least  disappear  from  the  feed  during  its  passage 
through  the  alimentary  canal. 

220.  Pentose  sugars.  —  In  general,  it  may  be  stated  that  the 
pentose  sugars  (in  particular  arabinose  and  xylose),  whether 
administered  by  the  stomach  or  injected  into  the  blood,  are  at 
least  partially  oxidized  in  the  body.     The  pentoses  differ  from 
the  hexoses  chiefly  in  the  fact  that  the  limit  of  tolerance  in  the 
blood  (215)  is  lower.     Excessive  amounts  of  hexose  carbohy- 
drates cause  an  excretion  of   sugar  in  the  urine.     The  same 
effect  is  produced  by  the  pentoses,  but  much  smaller  quantities, 
relatively,  are  required  to  bring  it  about. 

Most,  although  not  all,  investigators  have  found  an  increase 
in  the  glycogen  of  the  liver  consequent  upon  the  ingestion  of 
pentoses,  but  in  every  case  it  has  been  the  ordinary  Ce  glycogen, 
indicating  that  the  effect  is  an  indirect  one. 

221.  Pentosans.  —  The    investigations    upon    the    soluble 
pentose  sugars  or  their  derivatives  just  referred  to  have  shown 
that  they  are  to  a  greater  or  less  extent  assimilable.     The  pen- 
tose carbohydrates  in  the  feed  of  herbivora,  however,  exist  to  a 
very  limited  extent,  if  at  all,  in  this  form.     They  are  chiefly 
polysaccharids,  being  either  pure  pentosans   or   combinations 
of  pentosans  and  hexosans.     In  discussing  the  nutritive  value 
of  these  pentosans,  it  seems  to  have  been  frequently  assumed  that 
they  are  converted  into  pentoses  during  digestion.     As  a  matter 
of  fact,  however,  there  is  no  direct  evidence  that  such  is  the  case, 
while  Kellner's  results  (129)  afford  reason  to  believe  that  they 
are  largely  fermented  along  with  cellulose,  yielding,  besides 
gaseous  products,  chiefly  organic  acids.     If  this  is   the  case, 
farm  animals  do  not  acquire  from  their  feed  any  considerable 
amounts  of  pentoses  and  conclusions  drawn  from  experiments 
with  the  pentose  sugars  regarding  the  nutritive  value  of  these 
substances   are   inapplicable   to   ordinary   stock  feeds.     Their 
true  value  in  the  latter  would  be  simply  that  of  the  products  of 
their  fermentation. 

The  organic  acids 

222.  Formation  in  digestion.  —  As  was  shown  in  Chapter 
IV  (128-130,  132),  a  considerable  proportion  of  both  the  hexose 
and  pentose  carbohydrates  contained  in  the  feed  of  herbivora 
undergoes  fermentation  in  the  digestive  tract,  giving  rise,  -in 


METABOLISM  159 

addition  to  gaseous  products,  to  the  formation  of  various  or- 
ganic acids.  In  particular,  the  constituents  of  the  cell  walls 
of  plants  appear  to  owe  their  apparent  digestibility  chiefly  to 
this  action  of  the  organized  ferments  of  the  alimentary  canal. 
While,  therefore,  the  organic  acids  are  chemically  distinct  from 
the  carbohydrates,  and  while  some  of  these  acids  are  contained 
as  such  in  the  feed,  the  amounts  produced  from  carbohydrates 
are  so  considerable  that  this  would  appear  an  appropriate 
point  at  which  to  consider  their  metabolism. 

Unfortunately,  however,  little  is  known  of  the  metabolism  of 
the  simpler  organic  acids,  beyond  the  fact  that  such  of  them 
as  have  been  subjected  to  experiment  are  katabolized  to  carbon 
dioxid  and  water,  not  more  than  traces  of  them  at  most  ap- 
pearing in  the  excreta.  A  portion  of  the  carbon  dioxid  pro- 
duced unites  with  alkalies  and  appears  in  the  urine  as  carbonates. 

223.  Analogy  with  carbohydrates.  —  It  is  interesting  to  re- 
call  in    this   connection    that    the    carbohydrates    themselves 
undergo  cleavage,  producing  lactic  or  even  acetic  and  formic 
acids,  before  their  final  oxidation  (219).     If  it  be  true  that  these 
latter  comparatively  simple  substances  are  those  whose  oxida- 
tion yields  most  of  the  energy  supplied  by  the  carbohydrates, 
there  would  seem  to  be  no  reason  why  the  same  acids  resorbed 
directly  from  the  digestive  tract  should  not  follow  the  same 
general  course  of  metabolism  and  have  substantially  the  same 
nutritive  value.     If  this  view  be  correct,  there  is  after  all  a  con- 
siderable similarity  between  the  metabolism  of  the  carbohy- 
drates and  that  of  their  fermentation  products. 

The  non-nitrogenous  matter  of  the  urine 

224.  Products  of  incomplete  katabolism.  —  It  has  been  im- 
plied in  the  foregoing  pages  that  the  digested  carbohydrates  of 
the  feed,  whatever  the  intermediate  stages  through  which  they 
may  pass,  are  ultimately  oxidized  to  carbon  dioxid  and  water. 
Of  the  ordinary  hexose  carbohydrates  this  is  doubtless  true,  but 
with  some  of  the  large  variety  of  substances  ordinarily  grouped 
together  in  the  conventional  scheme  of  feeding  stuffs  analysis 
as  "  carbohydrates  and  related  bodies,"  or  as  "  crude  fiber  " 
and  "  nitrogen-free  extract,"  the  case  appears  to  be  otherwise. 

It  has  been  shown  that  the  urine,  in  addition  to  the  nitrogenous 


160  NUTRITION  OF  FARM  ANIMALS 

products  of  protein  katabolism  which  will  be  considered  in  the 
following  section,  contains  also  non-nitrogenous  materials, 
presumably  arising  from  the  incomplete  katabolism  of  ingredi- 
ents of  the  feed.  In  the  urine  of  man  and  of  the  carnivora  these 
non-nitrogenous  substances  are  chiefly  or  wholly  such  as  might 
be  derived  from  the  katabolism  of  proteins  (phenols  and  other 
compounds  of  the  aromatic  series),  and  their  amount  is  com- 
paratively small.  In  the  urine  of  herbivora,  particularly  of 
ruminants,  however,  their  quantity  is  relatively  very  consid- 
erable, and  it  seems  impossible  to  regard  any  large  portion  of 
them  as  products  of  protein  katabolism. 

225.  Origin.  —  Apparently    these    non-nitrogenous    organic 
substances  originate  in  some  way  from  the  roughages.     Their 
proportion  in  the  urine  is  relatively  large  when  the  ration  con- 
sists exclusively  of  roughage,  and  the  addition  of  such  feeding 
stuffs  to  a  basal  ration  causes  a  marked  increase  in  their  amount, 
while,  on  the  other  hand,  such  concentrates  as  have  been  in- 
vestigated do  not  produce  this  effect  to  any  very  considerable 
extent.     Furthermore,   their  amount  seems  to  bear  no  fixed 
relation  to  the  protein  of  the  feed.     When  the  amount  of  the 
latter  ingredient  is  small,  the  total  organic  matter  of  the  urine 
has  in  some  cases  exceeded  the  digested  protein  of  the  feed,  thus 
demonstrating  that  a  portion  at  least  of  the  non-nitrogenous 
urinary  constituents  must  have  had  some  other  source.     As 
the  proportion  of  protein  in  the  feed  increases,  the  amount  of 
nitrogenous  products  in  the  urine  likewise  increases,  while  that 
of  the  non-nitrogenous  products  appears  to  be  more  constant, 
so  that  the  ratio  of  urinary  nitrogen  to  carbon  increases.     The 
most  plausible  explanation  of  these  facts  seems  to  be  that  the 
substances  in  question  are  derived  from  some  of  the  non-nitroge- 
nous ingredients  of    the  roughages,  but  from  what  ones,  or 
what  is  the  nature  of  the  products,  we  are  still  ignorant. 

§  4.   THE  METABOLISM  or  THE  SIMPLE  PROTEINS 

Anabolism 

226.  Synthesis  of  proteins  from  digestive  products.  —  The 
simple  proteins  are  resorbed  (139,  152)  in  the  form  of  com- 
paratively simple  cleavage  products;    largely  as  amino  acids 
but  in  part  perhaps  as  more  or  less  complex  polypeptids.     Out 


METABOLISM  l6l 

of  these  substances  the  body  builds  up  the  great  variety  of 
specific  proteins  which  are  peculiar  to  itself  and  which  differ  in 
properties  and  chemical  structure  from  the  proteins  of  the  feed, 
especially  from  those  of  the  vegetable  kingdom  (147).  This 
process  of  building  animal  proteins  from  the  fragments  of 
vegetable  proteins  is  the  most  conspicuous  example  at  once  of 
the  synthetic  powers  of  the  animal  organism  and  of  the  object 
of  the  digestive  cleavage. 

227.  Seat  of  protein  synthesis.  —  As  regards  the  place  where 
this  synthesis  of  proteins  occurs,  opinions  are  divided.  Until 
recently,  most  experimenters  have  not  been  able  to  detect  the 
products  of  digestive  cleavage  with  certainty  in  the  blood,  either 
in  the  general  circulation  or  in  the  portal  vein,  and  the  current 
view  has  been,  therefore,  that  of  Abderhalden,  viz.,  that  the 
"  building  stones "  of  the  proteins  are  synthesized  in  the 
epithelial  cells  of  the  intestine  and  that  the  resulting  proteins 
—  in  particular  serum  albumin  —  are  passed  on  to  the  blood 
to  serve  as  nourishment  to  the  protein  tissues  of  the  body. 

Various  investigators,  however,  have  reported  the  presence  in 
the  blood  of  greater  or  less  amounts  of  non-protein  nitrogen 
and  with  the  aid  of  more  refined  chemical  methods  Folin  and 
Denis1  and  Van  Slyke  and  Meyer2  seem  to  have  shown  beyond 
question  that  amino  acids  may  pass  through  the  resorbing 
epithelium  unchanged  and  be  found  in  the  blood  and  tissues 
in  amounts  sufficient  to  account  for  practically  all  that  was 
administered  (152).  The  latter  experimenters  have  likewise 
shown  that  after  meat  feeding  the  proportion  of  amino  acids  in 
the  blood  may  be  doubled  and  that  the  increase  affects  the  blood 
of  the  entire  circulatory  system  and  not  that  of  the  portal  vein 
only,  while  Abel,3  by  a  diffusion  method,  has  been  able  to 
secure  considerable  amounts  of  amino  acids  from  the  circulat- 
ing blood  of  living  animals.  The  evidence  at  the  present  time, 
therefore,  seems  decisively  in  favor  of  the  view  that  the  frag- 
ments into  which  the  protein  molecule  is  split  during  digestion 
pass  without  material  change  into  the  blood  current  and  serve 
as  a  common  source  from  which  the  proteins,  both  of  the  blood 
and  the  various  tissues,  are  built  up  and  that  every  living  cell, 
each  in  its  own  measure,  has  this  anabolic  power. 

1  Jour.  Biol.  Chem.,  11  (1912),  87.  2  Jour.  Biol.  Chem.,  12  (1912),  399. 

3  Jour.  Pharmacol.  and  Expt'l  Therap.,  5  (1914),  275. 
M 


1 62  NUTRITION  OF   FARM  ANIMALS 


Katabolism 

228.  Nitrogenous  end  products.  —  The  total  katabolism  of 
the  proteins  results  in  the  elimination  of  all  their  nitrogen 
through  the  kidneys  in  the  form  of  the  various  relatively  simple 
crystalline  products  found  in  the  urine.  Of  the  nitrogenous 
excretory  products  of  man  and  the  carnivora,  urea  is  the  most 
prominent,  while  others,  such  as  uric  acid,  creatin,  creatinin, 
ammonia,  etc.,  are  of  subordinate  importance  quantitatively. 
Traces  of  hippuric  acid  are  also  found  in  the  urine  of  man  and 
carnivora,  while  it  is  present  in  relatively  large  amounts  in  that 
of  herbivora  along  with  considerable  quantities  of  ammonia 
and  apparently  but  little  urea. 

The  nitrogenous  ingredients  of  the  urine  of  mammals  other 
than  those  just  mentioned  are  either  derived  chiefly  from  the 
nucleoproteins,  whose  metabolism  will  be  considered  later, 
or  are  present  in  such  small  amounts  as  to  call  for  no  special 
consideration  from  the  present  very  general  point  of  view. 
Finally,  it  should  be  noted  for  completeness  that  a  small  amount 
of  nitrogenous  products  is  eliminated  in  the  perspiration  and 
also  that  from  one  point  of  view  the  incompletely  katabolized 
nitrogenous  excretory  products  of  the  feces  (154)  may  also  be 
regarded  as  products  of  protein  katabolism. 

Urea,  or  dicarbamid,  CO  (NH2)2,  is  the  chief  nitrogenous  product 
of  the  katabolism  of  the  simple  proteins  in  carnivora  and  omnivora. 
In  human  urine  from  80  to  90  per  cent  of  the  nitrogen  is  ordinarily 
present  in  this  form,  although  the  proportion  may  be  considerably 
diminished  under  special  conditions,  notably  on  a  low  protein  diet. 
Urea,  however,  is  not  simply  split  off  as  such  from  the  proteins  as 
some  earlier  schematic  statements  have  sometimes  been  taken  to 
imply.  The  immediate  antecedent  of  urea  is  ammonium  carbonate, 
which  undergoes  a  dehydration  in  the  liver  or  elsewhere,  while  there 
is  evidence  in  favor  of  the  view  that  the  ammonia  is  brought  to  the 
liver  in  the  form  of  ammonium  lactate.  At  any  rate  it  is  an  accepted 
fact  that  most,  if  not  all,  of  the  nitrogen  of  the  simple  proteins  passes 
through  the  ammonia  stage  on  its  way  to  excretion  as  urea.1  That 
the  formation  of  urea  from  ammonia  is  not  exclusively  a  function  of 
the  liver  is  shown  by  the  fact  that  it  still  continues  when  this  organ 
is  excluded  from  the  circulation  by  means  of  an  Eck  fistula. 

1  It  has  been  shown  that  the  liver,  kidneys  and  other  organs  contain  an  enzym 
which  splits  off  the  guanidin  group  from  arginin  (47)  producing  urea  and  ornithin. 


METABOLISM 


Hippuric  acid  in  small  amounts  is  a  normal  constituent  of  the 
urine  of  mammals  but  is  especially  abundant  in  that  of  herbivora. 
Its  formation  is  the  result  of  a  synthesis  (204).  When  benzoic  acid 
or  other  compounds  containing  the  benzoyl  radicle  are  introduced 
into  the  circulation  they  are  paired  with  glycin,  one  of  the  cleavage 
products  of  the  proteins,  in  the  kidneys  and  excreted  as  hippuric 
acid,  which,  chemically,  is  benzoyl-glycin,  or  benzamidoacetic  acid, 
(C6H5  •  CO)NHCH2  •  COOH.  The  normal  presence  of  small  quan- 
tities of  hippuric  acid  in  the  urine  arises  from  the  fact  that  the  putre- 
faction of  the  proteins  in  the  intestines  yields  compounds  containing 
the  benzoyl  radicle  which  are  resorbed  and  combine  with  glycin  to 
form  hippuric  acid.  But  a  small  proportion  of  the  hippuric  acid  pro- 
duced by  herbivora  can  be  thus  accounted  for,  however.  Most  of  it 
appears  to  owe  its  origin  to  the  roughages  consumed  by  these  animals, 
especially  those  derived  from  plants  of  the  gramineae,  while,  on  the 
other  hand,  concentrates  do  not  seem  to  increase  its  amount.  Ap- 
parently its  formation  bears  some  relation  to  some  of  the  ingredients 
of  the  cell  walls,  but  to  what  ones  in  particular  is  not  clear. 

229.  The  non-nitrogenous  residue.  —  In  addition  to  the 
nitrogenous  products  eliminated  in  the  urine,  the  complete 
oxidation  of  the  protein  molecule  gives  rise  to  the  production 
of  considerable  amounts  of  carbon  dioxid  and  water,  which  are 
excreted  through  the  same  channels  as  those  derived  from  the 
katabolism  of  carbohydrates  or  fats.  To  put  the  matter  in  the 
reverse  way,  while  the  urinary  products  account  for  all  the 
nitrogen  of  the  protein,  they  contain  but  a  relatively  small 
part  of  its  carbon,  hydrogen  and  oxygen.  This  is  clearly  shown 
by  comparing  the  average  amounts  of  these  elements  in  100 
parts  of  protein  with  the  quantities  contained  in  the  urea 
corresponding  to  the  total  nitrogen  of  the  protein.  Disregard- 
ing the  sulphur  of  the  proteins,  the  results  of  such  a  computation 
are  as  follows :  — 


PROTEINS 

UREA 

RESIDUE 

Carbon 

C5  o 

6  86 

46.16 

Hydrogen                               .     .          ... 

7  o 

2.  2O 

4.71 

Oxygen    
Nitrogen       

24.0 
26.0 

Q.I4 

16.00 

14.86 

IOO.O 

34-29 

65-71 

1 64  NUTRITION  OF  FARM  ANIMALS 

After  abstracting  the  elements  of  urea,  there  remains  con- 
siderably over  half  the  hydrogen  and  oxygen  of  the  protein  and 
the  larger  part  of  its  carbon.  A  substantially  similar  result  is 
reached  in  case  of  the  other  nitrogenous  metabolic  products. 
The  splitting  off  of  these  products  from  the  proteins  leaves  a 
non-nitrogenous  residue. 

230.  Two  stages  of  protein  katabolism.  —  Two  general  stages 
in  the  katabolism  of  the  proteins  may  be  distinguished.     The 
first  is  a  hydrolysis  by  which  the  proteins  are  split  up  into  their 
constituent  amino  acids.     The  second  is  a  deaminization  of 
the  amino  acids  in  which  the  nitrogen  of  these  acids  is  split  off 
as  ammonia. 

231.  Protein  hydrolysis.  —  The  first  stage  in  the  katabolism 
of  the  body  proteins  is  a  hydrolytic  cleavage,  more  or  less 
similar  to  that  effected  in  digestion  and  like  the  latter  brought 
about  by  enzyms,  which  in  this  case  are  contained  in  the  body 
cells  —  the  intracellular  enzyms  (209). 

The  truth  of  this  view  is  attested  by  the  facts  that  the  pres- 
ence of  proteases  in  almost  all  of  the  tissues  and  organs  of  the 
body  has  been  demonstrated  and  that  under  proper  conditions 
they  effect  a  rapid  solution  of  the  tissue  proteins  —  the  so-called 
autolysis.  Further  confirmation  is  afforded  by  the  known 
facts  regarding  the  transformation  of  one  protein  into  another 
in  the  body,  while  finally  the  production  in  the  organism  of 
some  of  the  cleavage  products  of  the  proteins,  presumably  as 
products  of  katabolism,  may  be  indirectly  shown. 

232.  Is  protein  hydrolysis  a  reversible   process  ?  —  If   the 
katabolism  of  body  proteins  is  initiated  by  an  enzymatic  cleav- 
age in  the  body  cells,  this  is  precisely  the  reverse  of  the  syn- 
thetic action  by  which  it  is  believed  that  body  proteins  are 
built  up  out  of  the  products  of  digestive  cleavage  (226),  and 
the  question  at  once  arises  whether  we  have  to  do  here  with  a 
reversible  enzym  reaction,  analogous  to  that  which  has  been 
suggested  as  occurring  in  the  case  of  the  carbohydrates  (214), 
the  general  nature  of  which  may  be  represented  by  the  formula 

Protein  ^  Amino  acids 

It  must  be  freely  admitted  that  proof  of  the  reversibility  of 
the  action  of  proteolytic  enzyms  is  as  yet  lacking,  such  phenom- 
ena as  the  formation  of  the  plasteins  discovered  by  Okunew 


METABOLISM  165 

and  the  alleged  formation  of  paraneuclein  by  the  action  of  pep- 
sin as  reported  by  Robertson  being  apparently  due  to  adsorp- 
tion phenomena.1  On  the  other  hand,  however,  many  authori- 
ties2 are  inclined  to  regard  reversibility  as  a  general  charac- 
teristic of  enzym  action  and  mere  negative  evidence  cannot,  of 
course,  disprove  this  belief.  At  any  rate  the  conception  of 
a  reversible  reaction  between  the  amino  acids  of  the  blood  and 
lymph  and  the  proteins  of  the  cells  affords  a  comparatively 
simple  and  unforced  explanation  of  the  facts  outlined  in  the 
foregoing  paragraphs,  as  well  as  of  others  relating  to  the  in- 
fluence of  the  supply  of  feed  protein  on  metabolism  which  will 
be  considered  later  (402).  In  particular,  it  may  be  observed 
that,  according  to  this  view,  by  no  means  all  the  amino  acids 
resorbed  into  the  blood  stream  would  undergo  synthesis  to 
proteins  but  that,  especially  if  the  amino  acid  supply  were 
liberal,  a  large  part  of  them  might  pass  directly  to  the  'second 
stage  of  protein  katabolism,  viz.,  deaminization. 

Finally,  since  the  proportions  of  the  single  amino  acids  sup- 
plied from  the  digestive  tract  vary,  one  must  conceive,  not  of 
a  single  reaction  between  protein  and  amino  acid,  but,  speak- 
ing broadly,  of  as  many  independent  reversible  reactions  as 
there  are  amino  acids  concerned. 

233.  Deaminization.  —  The  second  general  stage  of  protein 
katabolism  seems  to  be  the  splitting  off  of  the  NH2  group  from 
the  amino  acids,  the  products  being  the  corresponding  or  closely 
related  non-nitrogenous  organic  acids  on  the  one  hand  and 
ammonia  on  the  other.  This  also,  it  would  appear,  is  a  case 
of  enzym  action,  although  the  discovery  of  deaminizing  enzyms 
in  various  tissues  is  comparatively  recent  and  its  biological  im- 
portance is  still  to  some  extent  speculative. 

The  ammonia  resulting  from  the  deaminization  of  the  amino 
acids  is  believed  to  be  the  immediate  antecedent  of  urea,  into 
which  it  is  rapidly  converted,  chiefly  although  not  exclusively 
in  the  liver  (228).  In  this  way  the  nitrogen  of  any  amino  acids 
resorbed  in  excess  of  the  immediate  demands  of  the  body  cells 
for  protein  building  material  is  promptly  converted  into  ex- 
cretory products  and  so  disposed  of,  while  the  larger  part  of 
their  carbon  and  hydrogen  remains  in  a  series  of  substances 

1  Compare  Rohonyi ;  Biochem.  Ztschr.,  53  (1013),  179- 

2  Compare  Bayliss;  The  Nature  of  Enzym  Action  (1908),  Chapter  V. 


1 66  NUTRITION  OF  FARM  ANIMALS 

bearing  a  more  or  less  close  relation  to  the  fatty  acids  and  to- 
gether constituting  the  "  non-nitrogenous  residue "  of  the 
proteins  (229). 

It  is  important  to  note  that  these  non-nitrogenous  products 
contain  the  larger  share  of  the  chemical  energy  of  the  original 
proteins,  the  ammonia  carrying  off  but  little  and  both  the  di- 
gestive cleavage  and  the  deaminization  being  nearly  isothermic 
processes.  The  cleavage  and  deaminization  of  proteins,  there- 
fore, do  not  necessarily  involve  a  destruction  of  their  nutritive 
value  and  the  excretion  of  a  given  amount  of  nitrogen  in  the 
urine  is  not  to  be  regarded  as  indicating  the  total  destruction 
of  a  corresponding  amount  of  protein.  It  has  ceased  to  exist  as 
protein,  but  its  non-nitrogenous  residue  is  made  up  of  substances 
which  are  closely  related  chemically  to  both  the  carbohydrates 
and  fats,  and  which,  like  these,  may  be  katabolized  to  supply 
energy. 

234.  Deaminization  reversible.  —  Since  deaminization  in  the 
body  appears  to  be  an  enzymatic  reaction,  it  is  natural  to  in- 
quire whether  in  this  case,  as  in  the  other  enzymatic  reactions 
already  considered,  there  is  any  evidence  that  the  reaction  is 
a  reversible  one. 

So  far  as  direct  experiments  with  deaminizing  enzyms  are 
concerned,  no  such  evidence  has  been  produced,  but  Knoop  l 
andEmbden  and  Schmitz2  have  demonstrated  a  fact  of  funda- 
mental significance  in  metabolism,  viz.,  that  amino  acids  may 
be  formed  in  the  body  from  ketonic  or  hydroxy  acids  and  am- 
monium salts.  In  other  words,  the  animal  body  can  manufac- 
ture some  at  least  of  the  "  building  stones  "  of  the  proteins, 
and  from  the  latter  presumably  the  proteins  themselves  (226), 
out  of  the  ammonium  salts  of  the  corresponding  ketonic  or 
hydroxy  acids.  The  full  significance  of  this  comparatively 
recent  discovery  is  not  yet  fully  apparent.  The  question  of  the 
utilization  of  ammonium  salts  will  be  considered  later.  In 
this  connection  the  important  fact  is  that  these  results  indicate 
that  the  reaction,  or  series  of  reactions,  by  which  deaminization 
takes  place  is  reversible,  so  that  the  whole  process  of  protein 
metabolism  may  be  represented  schematically  as  follows :  — 

-04--     ^.  A     •          -j   ->  [  Organic  acids 
Proteins  X  Ammo  acids  2.  S   • 

[  Ammonia 

1  Ztschr.  Physiol.  Chem.,  67  (1910),  489.          2  Biochem.  Ztschr.,  29  (1910),  423. 


METABOLISM  167 

235.   Formation   of  carbohydrates  from  proteins. — It  has 

already  been  stated  (216)  that  carbohydrates  may  be  manu- 
factured, in  the  bodies  of  carnivorous  animals  at  least  and 
probably  in  those  of  other  species,  but  the  question  whether 
the  proteins  or  the  fats  or  both  serve  as  the  source  was  left 
open. 

Without  entering  into  experimental  details,  it  may  be  stated, 
as  the  general  result  of  many  trials  in  which  the  possibility 
of  a  production  from  fats  was  excluded  as  completely  as  pos- 
sible, that  carbohydrates  have  been  produced  in  such  large 
amounts,  and  in  quantities  so  closely  paralleling  the  quantities 
of  protein  katabolized,  as  to  amount  to  a  proof  of  their  formation 
from  the  latter.  The  acceptance,  however,  of  the  view  that 
carbohydrates  may  be  a  product  of  protein  katabolism  by  no 
means  excludes  the  possibility  of  their  formation  also  from  fats. 
Indeed,  in  view  of  the  importance  of  carbohydrates  in  metab- 
olism it  seems  altogether  likely  that  the  body  has  the  power 
to  manufacture  them  from  both  fats  and  proteins,  while,  as 
already  stated  (217),  the  reverse  process  of  the  formation  of 
fats  from  carbohydrates  has  been  demonstrated. 

With  the  increasing  knowledge  of  the  details  of  protein 
katabolism  afforded  by  recent  investigations,  the  question 
under  consideration  has  assumed  a  somewhat  different  aspect, 
the  discussion  shifting  from  the  fate  of  the  proteins  as  a  whole 
to  that  of  the  single  amino  acids  and  of  the  non-nitrogenous 
products  of  their  katabolism.  It  has  been  shown,  especially 
by  the  work  of  Lusk  and  his  associates,  that  some  at  least  of  the 
amino  acids  (glycin,  alanin,  aspartic  acid,  glutamic  acid,  histi- 
din),  after  deaminization  may  yield  dextrose.  In  the  case  of 
glycin  and  alanin  all  the  carbon  of  the  amino  acid  could  be  re- 
covered in  the  form  of  dextrose.  In  the  case  of  aspartic  and 
glutamic  acids,  on  the  other  hand,  only  three  out  of  the  four  or 
five  carbon  atoms  respectively  were  found  in  the  dextrose  pro- 
duced. Still  other  amino  acids,  notably  leucin  and  tyrosin, 
apparently  do  not  yield  dextrose,  but  instead  compounds  like 
/3  hydroxybutyric  acid  and  aceto-acetic  acid  which  are  the 
distinctive  products  of  the  katabolism  of  the  higher  fatty  acids 
(252). 

In  the  case  of  some,  then,  but  apparently  not  all,  of  the  prod- 
ucts of  protein  katabolism,  the  relations  between  protein  and 


1  68  NUTRITION  OF   FARM  ANIMALS 

carbohydrate    metabolism    may    be    schematically    expressed 
thus  :  - 

Glycogen  $  Dextrose  ^\ 

X*  ("  Lower  fatty  acids  ->  CO2  and  H2O 
Proteins  ^  Amino  acids  $  1 

INHs-  —  >Urea 


236.  Formation  of  fat  from  proteins.  —  Since  the  non-nitrog- 
enous products  of  protein  katabolism  appear  to  consist  largely 
of  comparatively  simple  substances  closely  related  to  the  lower 
members  of  the  fatty  acid  series,  and  since  some  at  least  of 
these  may  in  all  probability  be  synthesized  to  carbohydrates, 
while  the  latter  can  undoubtedly  give  rise  to  fats,  it  is  natural 
to   conclude   that    the   non-nitrogenous   products    of   protein 
katabolism  may  serve  as  a  source  of  fat,  either  by  direct  syn- 
thesis of  the  simpler  fatty  acid  chains  or  possibly  by  way  of 
the  carbohydrates.     The  conclusion  is  one  which    has  been 
hotly  debated  and  much  of  the  earlier  evidence   in  its  favor 
has  been  shown  to  be  inconclusive.     The    experimental  evi- 
dence may  be  more  conveniently  considered  in  connection  with 
a  discussion  of  the  sources  of  animal  fat  (247-249).     For  the 
present,  it  may  suffice  to  say  that  the  formation  of  fat  from 
protein  seems  altogether  probable,  but  that  on  the  other  hand 
the  amount  of  fat  thus  formed  under   normal   conditions  is 
usually  unimportant. 

§  5.   THE  METABOLISM  or  THE  NUCLEOPROTEINS 

The  metabolism  of  the  conjugated  proteins,  with  the  excep- 
tion of  the  nucleoproteins,  offers  few  features  of  special  in- 
terest. In  general  it  may  be  said  that  they  are  split  up  into  their 
constituents  during  digestion  and  that  the  cleavage  products 
undergo  substantially  the  same  metabolic  changes  as  if  con- 
sumed by  the  animal  in  the  uncombined  form.  In  the  case  of 
the  nucleoproteins,  however,  the  metabolism  of  the  nucleic 
acid  portion  of  the  molecule  calls  for  more  specific  consider- 
ation. 

Anabolism 

237.  Fate  of  digestive  products.  —  The  nucleic  acids  undergo 
extensive  enzymatic  cleavages  in  digestion  (139),  the  products 


METABOLISM  169 

passing  into  the  circulation  being  essentially  phosphoric  acid, 
pentoses,  and  purin  and  pyrimidin  bases.  By  analogy,  with 
the  simple  proteins,  one  might  expect,  therefore,  to  find  that 
these  fragments  of  the  nucleic  acid  molecule  are  rebuilt  into 
nucleoproteins  in  the  body  cells,  of  which  they  constitute  such 
an  indispensable  ingredient  (75). 

The  occurrence  of  such  a  synthesis,  however,  has  been  seriously 
questioned.  One  argument  against  it  is  the  fact  that  the  in- 
gestion  of  nucleoproteins,  or  more  specifically  purin  bases,  re- 
sults in  a  prompt  excretion  in  the  urine  of  end  products  of  their 
katabolism  which,  although  it  has  not  been  proved  to  be  quan- 
titative, is  certainly  large,  while  the  amounts  excreted  on  a 
purin  free  diet  are  small  and  notably  uniform.  It  has  been 
argued,  therefore,  that  the  so-called  "  exogenous  "  purins,  i.e., 
the  nucleic  acid  constituents  derived  from  the  feed,  are  simply 
katabolized  and  excreted  without  serving  to  rebuild  nucleic 
acids  in  the  cells.  Precisely  the  same  argument  might  be  made, 
however,  against  the  synthesis  of  the  simple  proteins  from  their 
cleavage  products,  since  in  this  case  also  an  increase  in  the  supply 
causes  a  prompt  and  almost  quantitative  increase  in  the  ex- 
cretion of  the  end  product,  urea  (402). 

238.  Autogenesis.  —  It  is  true  that  the  formation  of  nucleo- 
proteins differs  from  that  of  the  simple  proteins  in  that  the 
latter  is  a  reconstruction  of  the  molecule  from  its  fragments  1 
rather  than  a  synthesis  in  the  stricter  sense,  while  it  has  been 
demonstrated  that  the  body  can  build  up  nucleic  acids  out 
of  a  feed  supply  containing  neither  purins,  pyrimidins  nor 
pentoses.  One  of  the  most  striking  instances  of  this  is 
seen  in  the  development  of  the  embryo  of  birds  and  insects. 
The  eggs  contain  practically  none  of  the  substances  just  men- 
tioned, yet  the  bodies  of  the  young  animals  contain  normal 
amounts  of  nucleic  acid.  Equally  significant  is  the  case  of  the 
'suckling  mammal, which  receives  in  the  milk  a  food  very  poor 
in  purins,  pyrimidins  and  pentoses,  yet  which  maintains  a  rapid 
growth  and  cell  multiplication  with  its  accompanying  formation 
of  nucleoproteins.  So,  too,  in  Osborne  and  Mendel's  extensive 
investigations 2  upon  the  nutritive  values  of  the  proteins,  normal 

1  The  possibility  of  the  formation  of  proteins  from  ammonia  (234)  is  of  little  sig- 
nificance under  ordinary  conditions  of  nutrition. 

2  Carnegie  Institution  of  Washington,  Publication  No.  156,  p.  85. 


1 70  NUTRITION  OF  FARM  ANIMALS 

growth  of  rats  through  two  generations  was  secured  on  purin- 
and  pyrimidin-free  feed.  Another  fact  pointing  in  the  same 
direction  is  that  the  body  does  not  appear  to  require  a  supply 
of  phosphorus  in  organic  combination  but  can  build  up  its 
organic  compounds  from  phosphates  (258). 

239.  Regeneration   from,   cleavage   products.  —  In   view   of 
the  capacity  of   the  body   to  produce  nucleoproteins  in   the 
entire  absence  of  their  constituent  "  building  stones  "  may  it 
be  supposed  that  when  the  latter  are  supplied  in  the  feed  they 
may  be  recombined  in  the  cells  somewhat  as  are  the '  amino 
acids  of  the  simple  proteins? 

No  positive  answer  can  be  given  to  this  question.  It  would 
seem,  however,  that  the  first  steps  in  the  autogenesis  of  the 
nucleoproteins  must  be  the  formation  of  pentoses  and  of  the 
purin  and  pyrimidin  bases,  i.e.,  of  precisely  those  substances 
which  result  from  the  digestive  cleavages.  Even  though  it  be 
assumed  that,  in  the  former  case,  they  are  produced  within  the 
cells  where  they  are  further  synthesized  to  nucleic  acid,  it  is 
not  altogether  clear  why  the  same  substances  brought  to  the 
cell  by  the  blood  current  should  not  be  available  for  the  same 
purpose.  Provisionally,  at  least,  it  seems  perfectly  possible  to 
regard  the  entire  stock  of  these  "  building  stones  "  contained 
in  the  body,  whether  derived  from  the  feed  or  produced  by  the 
body  cells,  as  potentially  available  for  the  regeneration  of 
nucleic  acids.  From  this  point  of  view,  the  increased  excretion 
of  purins  which  results  from  their  ingestion  would  be  con- 
sidered as  a  consequence  of  their  increased  concentration  in 
the  blood  and  as  analogous  to  the  increased  excretion  of  urea 
which  follows  the  ingestion  of  simple  proteins  or  of  amino 
acids  (402). 

Katabolism 

240.  Cleavages.  —  The    katabolism    of    the    nucleic    acids 
bears  a  close  general  resemblance  to   that  of  the  simple  pro- 
teins.    As  in  the  case  of  the  latter,  the  first  general  stage  of  the 
process  consists   of  a  series   of   enzymatic   cleavages.     These 
cleavages  are  quite  analogous  to  those  of  the  simple  proteins 
and  yield  as  final  products  the  comparatively  simple  "  building 
stones  "  of  the  nucleic  acids.     Since  it  is  to  be  supposed  that 
the  autogenesis  (238)  of  these  compounds  is  via  these  same 


METABOLISM  171 

"  building  stones  "  it  would  appear  that  we  have  here,  as  in  the 
case  of  the  simple  proteins,  a  complex  of  reversible  enzym 
reactions. 

Phosphoric  acid 


Nucleic  acid 


Pentose 

Purin  or  pyrimidin  bases 


241.  Deaminization.  —  The  phosphoric  acid  which  is  split 
off  from  the  nucleic  acids  is,  of  course,  added  to  the  general 
stock  of  this  substance  in  the  body.     The  pentose  may  be  pre- 
sumed to  be  katabolized  or  possibly  built  up  into  a  hexose. 

The  bases,  on  the  other  hand,  like  the  amino  acids  derived 
from  the  proteins,  undergo,  as  the  second  general  stage  of  their 
katabolism,  an  enzymatic  deaminization  and  oxidation.  The 
NH2  groups  are  split  off  as  ammonia  and  converted  into  urea, 
while  the  ring  formations  are  largely  unbroken,  the  principal 
end  products  of  purin  katabolism  being  uric  acid  in  man  and 
allantoin  in  most  other  mammals.  Of  the  katabolism  of  the 
pyrimidin  bases  little  is  known.  The  deaminization  is  never 
complete,  however,  purin  and  pyrimidin  bases  appearing  in 
the  urine  along  with  the  end  products  of  katabolism. 

242.  Synthesis  of  uric  acid.  —  In  birds  and  reptiles,   uric 
acid  is  the  principal  nitrogenous  constituent  of  the  semi-solid 
urine.     Since  no  considerable  portion  of  its  nitrogen  can  have 
existed  as  preformed  purins  in  the  feed,  it  is  evident  that  these 
animals    must    synthesize  uric  acid.     This  synthesis  appears 
to  take  place  in  the  liver,  the  antecedents  probably  being  lactic 
acid  and  urea. 

§  6.  THE  METABOLISM  OF 'THE  FATS 
Anabolism 

243.  Re  synthesis  of  feed  fat.  —  In  considering  the  resorp- 
tion  of  the  fats  (152)  it  was  shown  that,  while  the  products  of 
their  digestion  are  glycerol  and  fatty  acids   (or  their  salts), 
after  resorption  only  neutral  fats  have  been  recognized  in  the 
epithelial  cells  and  in   the  lymph  of  the  intestinal  lacteals. 
The  cleavage  of  the  fats  in  digestion  is  reversed  in  the  epithelial 
cells.     It  seems  altogether  plausible  to  ascribe  this  resyn thesis 
to  the  action  of  an  intracellular  lipase,  the  more  since  the  action 


172  NUTRITION  OF   FARM   ANIMALS 

of  lipase  has  been  shown  to  be  reversible  in  some  cases  (211). 
Whether  this  resynthesis  be  regarded  as  part  of  the  process  of 
resorption  or  be  classed  as  one  of  the  metabolic  processes  is  a 
matter  of  indifference.  In  either  case  the  material  transmitted 
to  the  blood  current  consists  substantially  of  fats. 

The  digested  fats  are  contained  in  the  lymph  in  the  emulsified 
form  and  in  this  state  pass  from  the  thoracic  duct  into  the  blood 
of  the  subclavian  vein.  The  blood  itself,  however,  although 
sometimes  containing  as  much  as  i  per  cent  of  fat,  does  not 
normally  carry  emulsified  fats,  and  the  fat  globules  entering  it 
from  the  thoracic  duct  do  not  long  persist.  The  nature  of  the 
change  is  still  uncertain ;  by  some,  it  has  been  regarded  as  a 
cleavage  into  fatty  acids  and  glycerol  and  by  others  as  a  union 
with  proteins.  But  whatever  the  nature  of  the  change  it  seems 
to  be  well  established  that  the  fat  of  the  blood  exists  in  some 
sort  of  combination  which  is  soluble  in  water  and  diffusible 
and  which  may  be  called  for  convenience  "  soluble  fat." 

244.  Storage  of  fat.  —  A  liberal  supply  of  fat  to  the  blood 
from  the  digestive  tract  may  give  rise  to  a  storage  of  reserve 
fat  in  the  adipose  tissues  (94)  of  the  body.     It  is  to  be  presumed 
that  this  deposition  of  reserve  fat  is  substantially  a  reversal  of 
the  process,  whatever  it  is,  by  which  it  was  brought  into  solu- 
tion in  the  blood,  the  "  soluble  fat  "  of  the  latter  passing  into 
the  cells  and  being  there  reconverted  into  the  emulsified  form 
and  so  giving  rise  to  the  globules  characteristic  of  fat  cells. 

245.  Formation  of  cell  lipoids.  —  The  fats  deposited  in  the 
adipose  tissues,  as  already  implied,  are  a  store  of  reserve  ma- 
terial, laid  aside  temporarily  from  the  body  metabolism  when 
the  feed  supply  is  more  than  adequate  for  immediate  needs. 

The  various  more  complex  lipoids  (37-39,  75),  however 
(cholesterins, .  lecithins  and  other  phosphatids,  cerebrosids, 
etc.),  appear  to  be  essential  ingredients  of  protoplasm  and  to 
perform  specific  functions  in  the  cell.  All  these  substances 
have  as  their  basis  fatty  acid  molecules  coupled  with  other 
groups  and  it  is  a  reasonable  assumption  that  the  former  are 
derived  from  the  "  soluble  fat  "  of  the  blood  and  synthesized 
in  the  cells  into  the  specific  lipoids  as  required. 

246.  Manufacture  of  fats.  —  But  while  the  feed  fats  may 
serve  as  a  source  of  body  fats,  the  organism  is  by  no  means 
dependent  upon  the  former  for  its  supply  of  these  substances, 


METABOLISM  173 

but  may,  as  has  already   been  indicated    (217,   236),    manu- 
facture fats  from  other  ingredients  of  its  feed. 

This  view,  first  propounded  by  Liebig  in  1843,  was  contrary 
to  the  opinion  then  prevailing  and  led  to  a  lively  controversy 
which,  however,  was  definitely  resolved  in  favor  of  the  newer  be- 
lief. Indeed,  the  feed  fats,  especially  in  case  of  herbivorous  ani- 
mals, are  usually  of  subordinate  importance  as  sources  of  body  fat, 
a  large  share  of  the  latter  being  produced  de  now  in  the  body. 
This  fact  explains  in  part  the  general  uniformity  of  composition 
of  the  body  fat  of  each  species.  The  steer  produces  beef 
fat  and  the  sheep  mutton  fat  on  substantially  identical  rations 
largely  because  the  fat  deposited  in  the  body  is  derived  only 
in  small  part  from  the  feed  fat,  most  of  it  being  produced  by  the 
specific  metabolic  activities  of  the  body  cells.  The  seat  of  this 
synthetic  production  of  fat,  however,  as  well  as  the  manner 
in  which  it  is  deposited  in  the  reserve  tissues,  are  still  unknown. 

The  sources  of  animal  fat 

247.  Experimental  evidence.  —  The  sources  of  animal  fat 
have  been  already  indicated.     Aside  from  whatever  feed  fat 
may  be  stored  up  in  the  adipose  tissues,  the  body  can  produce 
fat  from  the  carbohydrates  of  the  feed  (217)  and  in  all  prob- 
ability from  the  non-nitrogenous  residue  of  the  proteins  (236). 
In  view  of  the  historic  interest  attaching  to  the  long  controversy 
over  this  question,  however,  as  well  as  of  its  intrinsic  importance, 
an  outline  of  the  experimental  evidence  seems  appropriate. 

That  the  feed  fat  is  a  source  of  body  fat  was  never  seriously 
questioned.  When  the  correctness  of  Liebig's  contention  that 
the  animal  body  can  also  manufacture  fat  had  been  demon- 
strated, it  was  assumed  that  the  source  of  this  new-formed 
fat  was  to  be  found  in  the  carbohydrates  of  the  feed  and  this 
was  for  years  the  accepted  view.  Following  Liebig's  termi- 
nology, the  proteins  were  designated  as.  the  "  plastic  materials," 
serving  to  build  up  tissue,  while  the  carbohydrates  and  fats  were 
"  respiratory  materials,"  serving  as  sources  of  heat  and  of  fat. 

248.  Fat  from  protein.  —  Several   earlier  investigators  ob- 
served facts  pointing  to  the  formation  of  fat  from  protein  in 
the  animal  body,  but  Carl  Voit l  was  the  first  to  distinctly  ad- 

1  Ztschr.  Biol.,  5  (1869),  79-169. 


174  NUTRITION  OF   FARM   ANIMALS 

vocate  the  belief  that  protein  constitutes  an  important  source 
of  animal  fat,  this  conclusion  being  based  largely  on  the  famous 
respiration  experiments  of  Pettenkofer  and  Voit  at  Munich  in 
which  a  dog  was  fed  lean  meat  freed  from  visible  fat  as  carefully 
as  possible  (this  being  the  nearest  practicable  approach  to  a 
pure  protein  diet)  and  the  balance  of  nitrogen  and  carbon 
(287,  292)  determined.  The  results  showed  in  many  cases  a 
retention  of  carbon  by  the  animal  greater  than  corresponded  to 
the  quantity  of  protein  gained,  and  this  difference  was  inter- 
preted, according  to  the  methods  described  in  Chapter  VI 
(293),  as  showing  a  production  of  fat. 

Pettenkofer  and  Volt's  experiments  were  long  accepted  as 
conclusive  until  Pflliger  l  subjected  them  to  destructive  criti- 
cism, showing  the  possibility  of  material  errors  in  the  estimates 
of  the  carbon  of  both  feed  and  visible  excreta. 

It  scarcely  need  be  said  that  this  result  does  not  prove  that 
fat  is  not  formed  from  protein,  but  simply  that  Pettenkofer  and 
Voit's  experiments  fail  to  demonstrate  it.  Of  later  experi- 
ments on  the  subject,  a  number  seem  to  show  clearly  the  for- 
mation of  a  small  amount  of  fat  from  protein,  even  after  every 
allowance  has  been  made  for  the  objections  raised  by  Pfliiger 
in  his  criticisms  of  the  experiments.  A  number  of  negative 
results  have,  it  is  true,  also  been  reported,  but  naturally  nega- 
tive results  are  of  much  less  value  than  positive  ones. 

Moreover,  the  indirect  evidence  in  favor  of  the  possibility 
of  the  formation  of  fat  from  protein  seems  practically  conclu- 
sive. As  already  stated  (235),  it  has  been  established  beyond 
reasonable  doubt  that  carbohydrates  may  be  produced  from 
protein  in  the  body.  If  this  is  true,  however,  it  almost  neces- 
sarily involves  the  possibility  of  the  formation  of  fats  from  pro- 
tein, since  carbohydrates  are  undoubtedly  a  source  of  fat. 

249.  Fat  from  carbohydrates.  —  Pettenkofer  and  Voit,2  how- 
ever, went  further  than  to  demonstrate,  as  they  believed,  the 
formation  of  fat  from  protein.  Their  experiments  included  a 
number  in  which  carbohydrates  were  added  to  a  ration  of 
protein  (lean  meat).  Assuming  with  Henneberg 3  that  100 
grams  of  protein  might  yield  51.4  grams  of  fat,  they  computed 
that  all  the  fat  produced  by  the  animal  in  these  experiments 

1  Arch.  Physiol.  (Pfluger),  51  (1892),  229. 

2Ztschr.  Biol.,  9  (1873),  435.  3  Lanclw.  Vers.  Slat..,  10  (1868),  455. 


METABOLISM  175 

could,  with  only  one  or  two  exceptions,  be  accounted  for  by  the 
fat  and  protein  of  the  feed.  They,  therefore,  characterized  the 
formation  of  fats  from  carbohydrates  as  improbable.  The  some- 
what general  impression  that  Voit  absolutely  denied  the  pro- 
duction of  fat  from  carbohydrates  is  incorrect,  although  he  re- 
garded it  as  improbable  and  unproved.  Indeed,  he  came  later  to 
admit  the  truth  of  the  opposite  view  and  even  furnished  from 
his  own  laboratory  experimental  evidence  in  its  support.  Never- 
theless, his  earlier  opinion  as  to  its  improbability  obtained  wide 
currency  and  in  the  hands  of  his  followers  became  almost  a 
dogma,  so  that  protein  was  given  a  vital  and  preponderant  im- 
portance the  effect  of  which  has  been  unfortunate  both  for  the 
development  of  the  science  of  nutrition  in  general  and  upon  the 
theory  of  stock  feeding  in  particular. 

Henneberg's  estimate  of  the  maximum  fat  production  from 
protein  was  soon  virtually  accepted  as  an  established  fact  and 
with  the  use  of  this  high  figure  it  was  easy  to  compute  from  most 
of  the  experiments  on  fat  production  then  on  record  that  the  fat 
and  protein  of  the  feed  were  sufficient  to  account  for  the  fat 
produced.  Similar  computations  upon  a  large  number  of  later 
feeding  experiments  l  yielded  similar  results,  so  that  belief  in 
the  non-formation  of  fat  from  carbohydrates  was  further 
strengthened. 

One  notable  exception  to  the  rule,  however,  were  the  experi- 
ments made  by  Lawes  and  Gilbert  in  1850  upon  the  fattening  of 
swine.  These  were  comparative  slaughter  tests  (284)  in  which 
the  gain  of  fat  was  determined  by  comparing  the  weight  and 
composition  of  similar  animals,  one  before  and  the  other  after 
fattening.  They  were,  accordingly,  subject  to  a  somewhat 
considerable  range  of  error,  but  even  on  the  most  extreme  as- 
sumptions it  was  impossible  in^six  out  of  the  nine  experiments 
to  account  for  the  fat  actually  produced  by  the  supply  of  fat 
and  protein  in  the  feed.  These  investigators,  therefore,  con- 
tinued to  maintain,  in  spite  of  much  adverse  criticism,  the 
formation  of  fat  from  carbohydrates,  although  their  experi- 
ments hardly  secured  the  recognition  which  they  deserved. 

As  time  went  on,  however,  results  began  to  accumulate  which, 
like  Lawes  and  Gilbert's  showed  a  much  larger  production  of 
fat  than  could  possibly  be  ascribed  to  the  fat  and  protein  of 

See  the  author's  Manual  of  Cattle  Feeding,  p.  177. 


176  NUTRITION  OF  FARM  ANIMALS 

the  feed.  This  was  particularly  the  case  as  it  came  to  be  more 
clearly  recognized  that  Henneberg's  estimate  of  a  production 
of  51.4  grams  of  fat  from  100  grams  of  protein  was  in  all  prob- 
ability too  high,  and  especially  after  it  was  shown  that  what 
had  been  regarded  as  digested  protein  in  many  of  these  experi- 
ments (i.e.,  digestible  N  X  6.25)  consisted  in  part  of  much 
simpler  nitrogenous  compounds.  The  ready  formation  of 
fat  by  the  hog  rendered  this  animal  a  very  suitable  subject  for 
experiment,  and  the  great  majority  of  investigations  on  this 
animal  have  supported  the  view  that  fat  is  produced  from 
carbohydrates,  but  similar  results  upon  other  species  have  not 
been  lacking,  while  respiration  experiments  upon  swine,  geese, 
dogs,  and  especially  the  extensive  investigations  by  G.  Klihn  l 
upon  cattle  have  completed  the  demonstration.2 

In  the  light  of  all  these  results,  the  formation  of  fat  from 
carbohydrates  in  the  animal  body  is  now  universally  admitted, 
while  its  production  from  protein  is  still  questioned  by  a  few 
and  in  any  case  is  of  little  economic  significance,  so  that  we 
have  come  back  by  a  curious  reversal  of  views  almost  to  Lie- 
big's  classification  of  the  nutrients  into  plastic  and  respiratory. 

This  conclusion  applies  specifically  to  the  pure  hexose  carbo- 
hydrates, particularly  starch.  In  many  of  the  experiments 
cited,  however,  the  non-nitrogenous  material  digested  by  the 
animal  consisted  to  a  not  inconsiderable  extent  of  those  sub- 
stances of  uncertain  chemical  nature  included  in  the  terms 
crude  fiber  and  nitrogen-free  extract.  Postponing  for  the 
present  any  discussion  of  the  nutritive  value  of  these  groups, 
it  may  suffice  to  say  here  that  Kellner's  investigations3  in 
particular  show  that  both  of  them,  including  the  pentosans,  may 
serve  as  sources  of  fat. 


Katabolism 

250.  Body  fat  a  reserve.  —  The  stored  fat  of  the  adipose  tis- 
sues, aside  from  its  mechanical  functions,  constitutes  the  great 
reserve  of  energy-yielding  material  in  the  body.  In  the  lack  of 
an  adequate  feed  supply,  common  observation  shows  that  this 

1  Kellner :   Landw.  Vers.  Stat. ;  44  (1894),  257. 

2  Compare  the  author's  Principles  of  Animal  Nutrition,  pp.  165-184. 
3 Landw.  Vers.  Stat.;  51  (1900). 


METABOLISM  177 

reserve  is  drawn  upon  for  the  support  of  the  internal  activities 
of  the  body  and  as  a  source  of  energy  for  the  performance  of 
external  work. 

251.  Mobilization  of  reserve  fat.  —  In  order  that  the  stored 
fat  may  be  used  for  the  general  metabolism  of  the  body  it 
must  first  be  transferred  from  the  adipose  tissue  cells  to  the 
localities  where  it  is  needed.     Presumably  this  is  accomplished 
by  its  reconversion  into  "  soluble  fat  "  and  its  passage  through 
the  walls  of  the  cells  into  the  blood,  that  is,  by  a  reversal  of 
the  process  by  which  it  was  laid  down.     Since  the  transfer  of 
fat  through  the  epithelial  cells  in  resorption  is  effected  by  a 
hydrolytic  cleavage  (152),  one  is  tempted  to  imagine  a  similar 
reversible  enzymatic  process  in  this  case.     Direct  evidence  of 
this  is  lacking,  but  apparently  such  a  cleavage  takes  place  some- 
where at  an  early  stage  in  the  katabolism  of  the  fats,  the  re- 
sulting glycerol  perhaps  serving  as  a  source  of  dextrose.     From 
that  point  on  the  katabolism  is ,  that  of  the  fatty  acids. 

252.  Oxidation  at  the  p  carbon  atom.  —  The  oxidation  of  the 
fatty  acids,  either  saturated  or  unsaturated,  to  carbon  dioxid 
and  water,  like  the  other  katabolic  processes  already  considered, 
is  a  step  by  step  process.     The  researches  of  Knoop,  Embden, 
Dakin  and  others  1  have  rendered  it  highly  probable,  if  not  cer- 
tain, that  the  oxidation,  at  least  in  the  case  of  the  normal  satu- 
rated acids,  begins  at  the  /3  carbon  atom  (i.e.,  at  the  second 
carbon  atom  from  the  COOH  group)  and  results  in  the  splitting 
off  of  two  carbon  atoms  at  a  time.     The  products  are  carbon 
dioxid,  water  and  a  fatty  acid  containing    two   less   carbon 
atoms  than  the  original  one  and  with  which  the  same  process 
of  erosion  is  repeated. 

If  it  be  true  that  the  fatty  acids  thus  undergo  katabolism  in 
the  body  by  stages  of  two  carbon  atoms  each,  and  particularly 
if  it  may  be  regarded  as  probable  that  they  may  be  built  up 
again  in  a  similar  manner  from  simpler  atomic  chains,  there 
is  afforded  a  plausible  explanation  of  the  rather  striking  fact 
that  nearly  all  of  these  compounds  found  in  the  animal  body 
contain  an  even  number  of  carbon  atoms. 

This  scheme  does  not  provide  for  the  oxidation  of  the  three 
lower  acids  of  the  series,  propionic,  acetic  and  formic,  and  in 

1  Compare,  Dakin,  Oxidations  and  Reductions  in  the  Animal  Body,  1912,  pp. 
17-47- 

N 


178  NUTRITION  OF   FARM   ANIMALS 

fact,  while  these  acids  are  known  to  be  freely  oxidized  in  the 
body,  the  chemical  mechanism  of  the  process  is  little  under- 
stood. 

253.  Formation  of  carbohydrates  from  fats.  —  In  discussing 
the  probability  of  the  formation  of  carbohydrates  from  pro- 
teins (235),  it  was  pointed  out  that  their  origin  might  often  be 
ascribed  to  either  proteins  or  fats  or  both.     It  was  there  shown 
that  in  many  cases  the  probabilities  strongly  favored  a  forma- 
tion from  proteins.     In  other  instances,  however,  the  proba- 
bilities seem  equally  strong  that  fats  give  rise  to  carbohydrates. 
In   particular,    experiments   upon   pjiloridzin   diabetes   of   the 
dog  have  shown  the  production  of  more  sugar  than  could  be 
formed  from  the  quantity  of  protein  katabolized  during  the 
same  time,  while  the  stock  of  glycogen  in  the  animals  experi- 
mented on  had  been  so  exhausted  by  fasting  and  muscular  work 
that  it  seems  scarcely  possible  to  interpret  the  results  other- 
wise than  as  showing  the  formation  of  sugar  from  fat.     It  should 
be  added,  however,  that  it  has  been  seriously  questioned  whether 
the  conditions  of  the  experiments  were  sufficiently  controlled 
to  warrant  the  conclusions  drawn. 

The  very  low  values  for  the  respiratory  quotient  (296)  which 
have  been  reported  in  some  cases  for  hibernating  animals  have 
also  been  interpreted  as  indicating  a  production  of  carbohydrates 
from  fat.  In  the  conversion  of  fat  into  sugar,  there  must  ob- 
viously be  an  absorption  of  oxygen  with  no  corresponding  evolu- 
tion of  carbon  dioxid,  the  tendency  of  which  would  be  to  lower 
the  respiratory  quotient.  The  value  of  the  latter  for  the  direct 
oxidation  of  fat  is  0.7.  In  hibernating  animals,  however, 
figures  as  low  as  0.3  have  been  reported,  while  the  weight  of  the 
fasting  animal  increased.  While  these  facts,  of  course,  do  not 
demonstrate  the  formation  of  sugar  from  fat,  they  are  quite 
compatible  with  that  interpretation  and  seem  to  indicate  a 
storage  of  oxygen.  The  more  recent  experiments  on  hibernat- 
ing animals,  however,  have  failed  to  give  such  low  quotients  as 
were  obtained  by  earlier  observers. 

§  7.    METABOLISM  OF  ASH  INGREDIENTS 

254.  Certain  chemical  elements  of  the  body  and  of  the  feed 
are  found  wholly  or  in  part  in  their  ash  when  these  materials 


METABOLISM  179 

are  burned  and  are  therefore  spoken  of  as  ash  ingredients,  al- 
though, as  already  pointed  out  (3,  5),  this  does  not  necessarily 
imply  that  they  existed  in  the  original  material  in  "  inorganic  " 
combination.  Most  of  these  elements  are  as  essential  to  the 
vital  processes  as  the  more  abundant  elements  carbon,  nitro- 
gen, hydrogen  and  oxygen  of  the  so-called  "  organic  compounds," 
although  unfortunately  the  laws  regulating  their  metabolism 
have  been  much  less  extensively  studied.  Among  these  ele- 
ments sulphur  and  phosphorus  are  of  special  importance  in 
this  connection. 

Sulphur 

255.  Sources.  —  While    feeding    stuffs    may    contain    small 
amounts  of  sulphur  in  the  form  of  sulphates,  by  far  the  greater 
part  of  this  element  in  the  feed  of  animals  exists  in  organic 
compounds.     Such,  for  instance,  are  the  allyl  sulphid  (CsHs^S, 
contained  in  garlic  and  other  members  of  the  genus  allium,  and 
the  allyl  sulphocyanat,  CsHs  •  CNS,  found  in  mustard  and  other 
genera  of  the  cruciferae.     Ordinarily,  however,  the  chief    car- 
riers of  organic  sulphur,  both  in  feeding  stuffs  and  animals, 
are  the  proteins,  which  contain  the  element  in  the  form  of  the 
di-amino  acid  cystin  (47). 

256.  Katabolism.  —  The  question  whether  the  animal  body 
can  build  up  its  sulphur  compounds  from  inorganic  sulphur 
does  not  appear  to  have  been  investigated. 

The  katabolism  of  the  cystin  component  of  proteins  pre- 
sumably follows  the  same  general  course  as  that  of  the  other 
amino  acids,  i.e.,  it  is  split  off  from  the  proteins  by  hy- 
drolytic  cleavage  and  subsequently  deaminized.  One  of  the 
products  of.  the  katabolism  of  cystin  appears  to  be  taurin, 
CH2  •  NH2  •  CH2  •  SOsH,  contained  in  the  taurocholic  acid  of  the 
bile.  To  the  extent,  therefore,  to  which  the  latter  com- 
pound escapes  resorption  in  the  lower  intestine,  it  carries  small 
amounts  of  sulphur  into  the  feces.  Both  cystin  and  taurin, 
however,  are  readily  oxidized  in  the  body,  the  larger  part  of 
their  sulphur  taking  ultimately  the  form  of  sulphuric  acid  and 
being  excreted  in  the  urine.  The  sulphuric  acid  of  the  urine 
exists  in  combination  in  part  with  aromatic  radicles  derived 
from  the  putrefaction  of  the  proteins  in  the  lower  intestine 
and  in  part  with  bases.  In  human  urine  about  one-fifth  of 


I  &0  NUTRITION  OF  FARM   ANIMALS 

the  total  sulphur  exists  in  a  less  completely  oxidized  form 
known  as  neutral  sulphur,  the  nature  and  origin  of  which  is 
obscure. 

Phosphorus 

257.  Forms  ingested.  —  The  phosphorus  supply  of  the  body 
is  received  substantially  in  the  four  forms  indicated  in  Chapter 
I  (5),  viz.,  as  phosphates,  as   phosphatids,  as  phospho-  and 
nucleo-proteins  and  as  phytin.     Of  these  the  various  "  organic  " 
forms  usually  predominate. 

It  appears  probable,  however,  that  all  these  various  forms  of 
phosphorus  are  resorbed  into  the  blood  stream  in  the  form  of 
phosphoric  acid.  Of  the  phosphates  ingested  as  such  this  is 
certainly  true.  There  seems  good  reason  for  believing  that  the 
phosphoric  acid  radicle  contained  in  the  nucleic  acid  of  the 
nucleoproteins  is  quite  completely  split  off  by  the  digestive 
enzyms  and  reaches  the  blood  as  phosphoric  acid  (139), and 
the  same  thing  is  presumably  true  of  the  phosphoproteins. 
The  phosphatids  are  probably  acted  on  by  the  Upases  of  the 
digestive  tract,  but  whether  the  glycerophosphoric  acid  resulting 
from  their  cleavage  is  further  split  up  is  unknown.  The  ready 
cleavage  of  phytin  in  seeds  would  suggest  that  probably  its 
phosphorus  also  is  resorbed  as  phosphoric  acid. 

258.  Anabolism  and  katabolism.  —  The  animal  body  contains 
a  large  store  of  phosphorus  in  the  "  inorganic  "  form,  especially 
in  the  skeleton.     For  the  maintenance  or  increase  of  this  store 
the  resorbed  phosphoric  acid  is  naturally  available. 

The  body  also  contains,  however,  organic  phosphorus  com- 
pounds, which,  although  less  in  amount  than  the  inorganic, 
are  of  the  highest  significance  for  the  vital  functions.  The  be- 
lief that  the  phosphorus  supply  of  the  body  is  resorbed  chiefly 
in  the  form  of  phosphoric  acid  necessarily  implies,  therefore, 
that  the  organism  is  able  to  utilize  inorganic  phosphorus  for  the 
synthesis  of  nucleic  acids,  phosphoproteins,  phosphatids,  etc., 
and  the  experimental  evidence  is  strongly  in  favor  of  this 
belief  (497).  In  this  respect,  as  in  many  others,  the  synthetic 
power  of  the  organism  appears  to  be  greater  than  was  long 
supposed. 

Little  is  known  regarding  the  course  followed  by  the  phos- 
phorus in  the  katabolism  of  the  nucleoproteins,  phosphatids, 


METABOLISM  181 

etc.  Ultimately  it  takes  the  form  of  phosphoric  acid  and  is 
excreted  in  the  feces  or  urine  (199),  but  whether  any  inter- 
mediate compounds  are  formed  is  not  known. 

Other  elements 

While  the  other  so-called  ash  ingredients  are  no  less  impor- 
tant than  the  two  just  considered,  little  is  known  regarding  their 
katabolism  in  the  ordinary  sense,  i.e.,  of  the  chemical  changes 
which  they  undergo  in  the  body.  That  they  may  exist  in 
feeding  stuffs  in  organic  as  well  as  in  inorganic  forms  is  probable. 
That  they  enter  into  organic  combination  in  the  animal  body  is 
likewise  to  be  assumed  but  is  positively  known  in  only  a  few 
instances  like  that  of  the  iron  of  the  haemoglobin  and  the 
iodin  of  the  thyroid  glands. 

259.  Sodium  and  potassium.  —  Both  sodium  and  potassium 
are  contained  in  the  ordinary  foods  and  feeding  stuffs  and  in 
addition  man  and  farm  animals  consume  not  inconsiderable 
amounts  of  common  salt,  although  it  appears  probable  that  this 
serves  to  a  considerable  extent  as  a  condiment  and  that  the 
amount  actually  necessary  is  less  than  is  often  supposed.     Bab- 
cock,  e.g.,  was  able  to  keep  cows  for  over  a  year  without  access 
to  salt,  except  that  contained  in  their  feed,  without  any  obvious 
ill  consequences. 

Both  potassium  and  sodium,  as  well  as  the  chlorin  com- 
bined with  the  latter  in  the  form  of  salt,  are  excreted  in  the 
urine. 

260.  Calcium  and  magnesium.  —  These  elements,  calcium  in 
particular,  are  especially  important  in  their  relations  to  the 
growth  and  maintenance  of  the  skeleton,  but  they  are  not  lacking 
in  the  soft  tissues  also,  where  they  perform  important  functions. 
Of  their  intermediary  metabolism  little  is  known.     As  noted 
in  Chapter  IV  (199),  the  normal  path  of  excretion  of  calcium, 
and  to  some  extent  of  magnesium,  is  through  the  lower  in- 
testine, so  that  the  apparent  digestibility  of  these  elements  is 
no  measure  of  the  amount  actually  resorbed  and  utilized  in  the 
body  processes. 

261.  Iron.  —  A  long  controversy  has  been  carried  on  over 
the  question  whether  inorganic  iron  may  be  resorbed  and  if  so 
whether  it  can  be  utilized  for  the  synthesis  of  the  haemoglobins 


182 


NUTRITION  OF   FARM   ANIMALS 


and  for  other  purposes  in  the  body.  Both  questions,  however, 
may  be  regarded  as  settled  in  the  affirmative.  The  matter  is 
of  importance  in  its  relations  to  the  use  of  iron  in  medicine  but 
is  of  no  special  significance  in  stock  feeding. 

The  excretion  of  iron  takes  place  almost  exclusively  through 
the  intestines  and  this  fact  led  to  the  earlier  conclusion  that 
inorganic  iron  cannot  be  resorbed. 

§  8.   FUNCTIONS  or  THE  NUTRIENTS 

262.  General  scheme  of  metabolism.  —  In  considering  the 
metabolism  of  the  several  classes  of  nutrients  in  the  foregoing 
paragraphs,  it  was  found  that  the  main  features  of  the  process 


FIG.  23.  —  Diagrammatic  scheme  of  metabolism. 

in  each  case  might  be  conceived  of  in  accordance  with  the  ideas 
suggested  in  §  2  (210-212)  as  consisting  of  a  complex  of  rever- 
sible reactions  accelerated  or  retarded  by  intracellular  enzyms. 
By  combining  the  equations  used  to  represent  those  reactions,  it 
appears  possible  to  take  a  further  step  and  formulate  the  fol- 
lowing highly  generalized  scheme  for  the  total  metabolism  which 
may  serve  to  show  the  interrelations  between  the  metabolism 


METABOLISM  183 

of  the  chief  classes  of  organic  nutrients.  For  the  sake  of  sim- 
plicity some  of  the  intermediate  steps  mentioned  on  previous 
pages  have  been  omitted.  The  central  portion  of  the  diagram 
includes  the  feed  substances  taken  up  into  the  blood.  At  the 
extreme  left  are  shown  the  main  groups  of  tissue  ingredients, 
and  at  the  extreme  right  the  excretory  products. 

It  cannot  be  too  strongly  emphasized  that  any  such  diagram 
as  the  foregoing  is  of  necessity  in  the  highest  degree  schematic. 

For  one  thing,  neither  the  enzymatic  nature  nor  the  revers- 
ibility of  the  changes  indicated  in  the  diagram  has  been  estab- 
lished except  in  a  few  cases.  As  already  pointed  out  (212), 
this  conception  of  the  nature  of  metabolism  is  still  to  a  large 
extent  hypothetical,  although  the  hypothesis  harmonizes  well 
with  the  present  state  of  our  knowledge. 

Moreover,  aside  from  the  mere  omission  from  the  diagram  of 
certain  recognized  products  of  the  intermediary  metabolism, 
the  chemical  processes  in  the  body  are  doubtless  infinitely  more 
complex  than  can  be  indicated  in  any  such  way.  A  vast  num- 
ber of  different  substances  have  been  identified  in  the  animal 
body,  many  of  which  are  known  to  have  important  functions 
in  keeping  the  organism  in  running  order  but  which  are  not 
even  hinted  at  in  this  scheme. 

In  brief,  the  scheme  is  concerned  with  the  results  of  the 
metabolic  processes  so  far  as  they  are  related  to  nutrition 
rather  than  with  the  mechanism  by  which  these  results  are 
brought  about.  It  seeks  to  show  in  outline  how  the  principal 
groups  of  nutrients  are  related,  on  the  one  hand,  to  the  building 
up  of  body  tissues,  and,  on  the  other  hand,  to  the  formation  of 
excretory  products,  and  to  indicate  the  mutual  relations  of  the 
several  groups.  For  this  purpose  it  may  perhaps  serve  a  use- 
ful end  as  an  aid  to  memory,  provided  its  limitations  are  clearly 
understood. 

263.  Dual  function  of  feed.  —  As  pointed  out  in  §  i  of  this 
chapter  (207),  the  animal  body  may  be  regarded  in  the  light  of 
a  transformer  of  energy.  By  the  agency  of  the  protoplasm  of 
its  cells,  in  ways  largely  hidden  from  us,  it  converts  the  chemical 
energy  supplied  in  its  feed  into  the  various  forms  characteristic 
of  living  matter.  From  this  point  of  view  the  feed  has  a  two- 
fold function. 

First,  the  feed  ingredients  are  carriers  of  energy.     The  higher 


1 84  NUTRITION  OF  FARM  ANIMALS 

plants  transform  the  radiant  energy  of  the  sun  into  the  chemical 
energy  of  their  various  constituents,  to  be  yielded  up  by  the 
latter  to  the  animal  organism  through  the  processes  of  metab- 
olism. This  conception  has  become  a  familiar  one  and  much 
emphasis  has  been  laid  upon  it  in  recent  years. 

Second,  the  feed  supplies  the  specific  materials  required  for 
building  and  maintaining  all  the  complex  structures  of  the 
body  and  for  their  harmonious  functioning,  i.e.,  it  is  the  source 
of  structural  and  repair  material. 

That  the  proteins,  fats  and  mineral  ingredients  which  make 
up  by  far  the  larger  part  of  the  dry  matter  of  the  body  (99,  280) 
are  derived  ultimately  from  the  feed  needs  no  special  demon- 
stration, but  the  importance  of  many  substances  present  in  the 
body  in  only  minute  amounts  tends  to  be  overlooked.  For 
example,  the  enzyms  of  the  body,  both  extra-  and  intra-cellular, 
form  no  considerable  portion  of  its  mass,  yet  they  are  essential 
to  its  vital  activities.  So,  too,  the  various  hormones  and  se- 
cretions of  the  ductless  glands,  while  ignored  in  the  broad  scheme 
of  metabolism  just  presented,  are  essential  to  the  vital  processes. 
Clearly,  the  feed  must  supply  material  for  the  production  of 
these  and  other  similar  substances. 

In  other  words,  no  amount  of  energy-yielding  material  will 
suffice  to  support  life  in  the  absence  of  those  specific  substances 
which  are  necessary  in  order  that  the  machinery  of  conversion 
shall  operate  properly,  much  as  *LO  amount  of  coal  under  the 
boiler  will  enable  an  electric  plant  to  furnish  a  normal  amount 
of  current  if  the  insulation  of  the  generator  is  defective.  For 
example,  if  tryptophan  is  necessary  for  the  formation  of  some 
essential  internal  secretion,  a  diet  lacking  that  substance, 
however  much  energy  it  might  furnish,  would  fail  to  support  the 
organism  permanently  unless  the  body  can  manufacture  trypto- 
phan from  other  substances. 

The  latter  qualification  is  a  very  important  one.  The  animal 
is  very  far  from  being  dependent  upon  the  presence  in  its  feed 
of  all  the  varied  chemical  compounds  required  for  its  operation. 
Indeed,  quite  the  reverse  is  the  case.  As  has  appeared  in  pre- 
vious sections,  the  actual  substances  resorbed  are  comparatively 
simple  and  uniform  and  upon  them  the  animal  body  executes 
a  great  variety  of  chemical  changes,  both  analytic  and  synthetic. 
What  is  necessary  is  that  the  resorbed  feed  shall  include  sub- 


METABOLISM  185 

stances  out  of  which  the  body  can  manufacture  the  compounds 
which  it  requires. 

264.  Functions  of  the  proteins.  —  The  proteins  furnish  at 
once  the  most  familiar  and  the  most  striking  example  of  this 
dual  function  of  the  feed. 

Since  the  proteins  may  be  katabolized  in  the  body  with  the 
formation  of  products  (carbon  dioxid,  water,  urea,  etc.)  con- 
taining either  no  available  energy  or  but  a  small  fraction  of 
that  found  in  the  original  proteins,  it  is  clear  that  the  latter 
serve  as  carriers  of  energy.  In  fact,  it  has  been  shown  to  be 
possible  to  maintain  a  carnivorous  animal  in  normal  activity 
for  an  indefinite  time  on  a  diet  containing  substantially  nothing 
but  protein  as  a  source  of  energy. 

But  proteins  serve  also  as  building  material.  Aside  from 
water,  the  working  machinery  of  the  body  is  composed  largely  of 
proteins,  while  very  many  at  least  of  the  special  substances 
already  mentioned  are  nitrogenous  and  probably  derived  from 
the  proteins.  These  protein  tissues  and  other  substances  must 
be  built  up  in  the  growing  animal  and  maintained  in  the  mature 
one,  and  for  this  purpose  only  proteins  or  their  cleavage  prod- 
ucts can  be  utilized,  and  their  presence  in  the  feed  is  indis- 
pensable. 

A  point  which  sometimes  causes  perplexity  is  that  the  same 
portion  of  protein  may  not  only  serve  as  structural  material 
but  also  yield  energy  for  the  vital  processes,  so  that  in  esti- 
mating the  energy  supplied  by  a  feeding  stuff  that  of  its  protein 
as  well  as  that  of  its  other  ingredients  is  included.  The  difficulty 
disappears,  however,  when  it  is  remembered  that  any  given 
portion  of  protein  does  not  perform  both  these  functions  at  the 
same  time.  If  a  gram  of  protein  in  the  feed  of  a  mature  animal 
is  used  for  structural  purposes  it  practically  takes  the  place  of 
an  equal  amount  of  tissue  protein,  while  the  latter  is  katabolized 
and  yields  substantially  the  same  amount  of  energy  as  would 
have  been  available  from  the  gram  of  feed  protein  had  that 
been  katabolized  instead.  The  latter,  with  its  store  of  energy, 
has  been  temporarily  set  aside  from  the  katabolic  process  but  at 
some  later  time  may  itself  be  replaced  by  another  gram  of  feed 
protein  and  katabolized  in  its  turn,  liberating  the  corresponding 
amount  of  energy.  The  repairing  of  a  wooden  building  may 
serve  as  an  illustration.  The  old  wood  taken  out  to  make  way 


1 86  NUTRITION   OF   FARM   ANIMALS 

for  new  material,  as  well  as  any  surplus  of  new  wood  over  that 
immediately  required,  may  be  used  indifferently  as  fuel  for 
warming  the  building.  The  case  of  the  young  animal,  in  which 
protein  is  permanently  set  aside  for  growth,  is  a  trifle  more  com- 
plex but  substantially  the  same  considerations  hold  good. 

265.  Functions  of  fats.  —  In  the  case  of  the  fats  the  energy- 
bearing  function  is  the  predominant  and  obvious  one.     Fats 
are  a  concentrated  form  of  fuel,  containing  much  more  energy 
per  unit  than  any  of  the  other  nutrients.     They  supply  much 
energy  in  a  small  bulk  and  are,  therefore,  well  adapted  for  the 
storage  of  reserve  energy  in  the  body. 

The  fats  and  closely  related  bodies  (the  lipoids),  however, 
are  also  important  and  apparently  essential  constituents  of 
protoplasm  (75).  The  lipoids,  therefore,  have  important 
structural  functions  and  an  adequate  supply  of  them  in  the 
body  is  indispensable.  From  this  point  of  view,  some  interest 
attaches  to  the  results  obtained  by  a  number  of  investigators 
who  claim  to  have  shown  that  a  certain  minimum  supply  of 
lipoids  in  the  feed  is  essential,  especially  for  growing  animals. 
The  evidence,  however,  is  negative  evidence,  i.  e.,  experimental 
animals  failed  to  grow  normally  on  a  lipoid-free  diet.  In  view 
of  the  positive  results  obtained  by  Osborne  and  Mendel,1  as  well 
as  of  the  fact  that  both  the  simple  fats  and  the  phosphatids,  at 
least,  can  be  synthesized  freely  in  the  organism,  and  taking  into 
consideration  the  extensive  synthetic  power  of  the  body  in 
general,  it  is  difficult  to  believe  that  the  presence  of  lipoids  in 
the  feed  is  indispensable,  and  more  recent  investigations  have 
afforded  a  different  explanation  of  the  observed  facts  (498).  On 
the  other  hand,  it  has  been  shown  that  the  lecithins  stimulate 
growth  and  also  that  the  fats  appear,  within  certain  limits,  to 
favor  the  production  of  milk  fat. 

266,  Functions  of  carbohydrates.  —  The  carbohydrates  even 
more  distinctly  than  the  fats  serve  chiefly  as  carriers  of  energy. 
While  containing  less  energy  per  unit  than  fats,  they  can,  on 
the  other  hand,  be  consumed  in  larger  quantities  and  they 
practically  supply  the  greater  part  of  the  energy  in  the  diet  of 
man  and  of  farm  animals.     While  the  presence  of  carbohydrates 
(dextrose)  in  the  blood  and  lymph  is  essential,  this  appears  to 
be  chiefly  on  account  of  their  ready  availability  as  fuel  material. 

1  Jour.  Biol.  Chem.,  12  (1912),  81. 


METABOLISM  187 

The  carbohydrates  seem,  however,  to  have  a  specific,  function 
in  relation  to  the  katabolism  of  fats.  When  the  body  is  com- 
pelled to  draw  its  energy  supply  chiefly  from  the  fats,  as  in 
fasting  or  in  diabetes  (in  which  the  power  of  katabolizing  car- 
bohydrates is  lost),  or  when  carbohydrates  are  absent  from  the 
diet,  the  katabolism  of  the  fats  fails  to  be  complete  and  con- 
siderable amounts  of  beta-oxybutyric  acid  as  well  as  the  ab- 
normal katabolic  product  aceton  are  excreted  unoxidized  in  the 
urine. 

267.  Non-nitrogenous  nutrients  in  general.  —  While  it  thus 
appears  that  both  the  fats  (or  lipoids)  and  carbohydrates  may 
serve  special  purposes  in  the  body,  it  is,  nevertheless,  clear 
that  their  chief  function  is  to  supply  energy.     Their  amounts  in 
ordinary  rations  are  so  abundant  that  as  compared  with  their 
functions  as   carriers   of  energy   any   specific   purposes  which 
they  serve  in  the  body  are  amply  provided  for.     As  related  to 
the  nutrition  of  farm  animals  in  particular,  it  is  of  special 
interest  to  note  that  not  only  the  fats  and  carbohydrates  di- 
gested as  such  but  also  the  products  of  the  bacterial  fermenta- 
tion of  the  insoluble  carbohydrates  are  available  as  sources  of 
energy. 

268.  Functions  of  ash  ingredients.  —  While  the  non-nitroge- 
nous organic  nutrients  serve  chiefly  as  carriers  of  energy  and 
only  in  a  minor  degree  to  provide  the  compounds  necessary  for 
the  performance  of  specific  bodily  functions,  the  so-called  ash 
ingredients  represent  the  other  extreme  in  this  respect.    They 
introduce  practically  no  available  energy  into  the  organism  but, 
on  the  other  hand,  they  are  not  only  essential  structural  com- 
ponents of  the  body  tissues  but  likewise  supply  and  maintain 
certain   conditions   indispensable    to    the   performance   of   the 
bodily  functions. 

The  structural  importance  of  the  ash  ingredients  is  most 
manifest  in  the  case  of  the  skeleton,  which,  in  the  higher  ani- 
mals, contains  relatively  large  amounts  of  calcium  and  phos- 
phoric acid  and  small  quantities  of  magnesium,  sodium  and 
carbonic  acid  (81)  which  impart  to  it  certain  necessary  me- 
chanical qualities  of  strength  and  rigidity.  The  necessity  for 
a  supply  of  these  substances  in  the  feed,  especially  in  that  of 
growing  animals,  is  too  obvious  to  require  discussion.  The 
ash  ingredients,  however,  have  other  equally  important  functions 


1 88  NUTRITION  OF  FARM  ANIMALS 

in  providing  the  necessary  conditions  for  the  chemical  and  physi- 
cal activities  of  the  various  tissues. 

269.  Osmotic  pressure.  —  The  cells  of  the  various  tissues 
draw  their  nourishment  from  the  lymph  which  constitutes  their 
immediate  nutritive  environment  (185)  and  from  which  they  are 
separated  by  cell  walls  which  partake  of  the  nature  of  semi- 
permeable  membranes.     In  order  to  maintain  normal  condi- 
tions in  the  protoplasm  of  the  cells  the  osmotic  pressure  of  the 
lymph,  and  therefore  that  of  the  blood  from  which  it  is  derived, 
must    be    maintained    approximately    constant.     The  osmotic 
pressure  of  the  blood  is  stated  to  be  approximately   about   8 
atmospheres,  due  largely  to  the  ash  ingredients  contained  in 
solution.     With  an  adequate  supply  in  the  feed  the  concen- 
tration of  mineral  matter  in  the  blood  is  regulated  chiefly  by 
the  excretory  activity  of  the  kidneys.     Thus,  in  the  case  of 
sodium  chlorid,  for  example,  it  is  estimated  that  the  blood  of 
an  average  man  contains  approximately  30  grams  of  this  sub- 
stance, of  which  hardly  half  a  gram  is  excreted  daily  when 
none  is  consumed.     If,  however,  salt  is  added  to  the  diet,  the 
excess  is  promptly  excreted  in  the  course  of  the  next  twenty- 
four  hours.     What  is  true  of  salt  in  this  respect  is  true  also  of 
other  diffusible  ingredients  of  the  blood. 

270.  Ionic  concentration.  —  The  various  salts  are  contained 
in  the  body  largely  in  dilute  aqueous  solution.     In  such  solu- 
tions, however,  it  is  believed  that  salts  are  largely  dissociated 
into  their  constituent  ions,  a  dilute  solution  of  common  salt, 
for  example,  containing  in  addition  to  some  unchanged  NaCl 
the  ions  Na  and  Cl,  one  of  calcium  sulphate  the  ions  Ca  and 
SO4,   etc.     Acids  are  similarly  dissociated,  yielding  hydrogen 
ions     (H2SO4^:H  +  SO4),    while    alkalies    yield     OH     ions 
(KOH  ^  K  +  OH) .     Some  of  these  ions  have  been  shown  to 
have  specific  effects  on  certain  cellular  activities.     For  example, 
a  frog  muscle  kept  in  0.7  per  cent  NaCl  solution  retains  its  irrita- 
bility for  one  or  two  days.     In  a  solution  of  a  non-electrolyte, 
like  sugar,  asparagin,  etc.,  having  the  same  osmotic  pressure,  the 
muscle  soon  loses  its  irritability,  but  if  NaCl  be  added  to  the 
solution  it  regains  it.     Since  a  number  of  other  sodium  salts 
produce  the  same  effect,  while  chlorids  of  other  metals  do  not, 
it  is  apparent  that  the  effect  is  due  to  the  Na  ions.     On  the 
other  hand,  Na  ions  alone  cause  long  continued  rhythmic  con- 


METABOLISM  189 

traction  of  muscles,  which,  however,  is  suspended  by  the  pres- 
ence in  the  solution  of  certain  (not  all)  dyad  ions  like  Ca  or  Mg. 
Numerous  other  examples  of  such  antagonistic  actions  of  ions 
are  known,  such  as  those  observed  by  Loeb,  for  example,  in 
the  development  of  the  egg.  In  general  it  may  be  said  that  cell 
activities  are  dependent  among  other  things  upon  a  suitable 
ionic  concentration  of  various  elements  in  their  surroundings, 
and  it  is  a  striking  and  interesting  fact  that  the  so-called  physi- 
ological salt  solutions  in  which  living  organs  may  be  kept  func- 
tionally active  for  a  longer  or  shorter  time  contain  the  various 
salts  in  approximately  the  same  proportions  as  are  found  in 
sea  water. 

Another  example  of  the  influence  of  ionic  concentration  is 
afforded  in  the  case  of  the  digestive  enzyms.  Ptyalin,  for 
example,  is  sensitive  to  a  very  slight  excess  of  hydrogen  ions. 
Pepsin,  on  the  other  hand,  is  most  active  in  the  presence  of 
hydrogen  ions,  while  trypsin  acts  best  in  the  presence  of  an 
excess  of  OH  ions. 

271.  Maintenance  of  neutrality.  —  Closely  connected  with 
the  foregoing  topic  and  constituting  indeed  a  special  case  of  it, 
is  that  of  the  maintenance  of  neutrality  in  the  body  fluids.  A 
fluid  is  neutral  in  the  chemical  sense  when  it  contains 
no  excess  of  H  nor  of  OH  ions,  an  excess  of  the  former  being 
equivalent  to  acidity  and  an  excess  of  the  latter  to  alkalinity. 
It  has  been  shown  that  the  blood  serum,  as  a  representative  of 
the  body  fluids,  is  very  nearly  neutral,  its  content  of  H  and 
OH  ions  being  approximately  0.4  X  io~7  and  7.2  X  io~7, 
i.e.,  it  has  an  alkalinity  equivalent  to  about  0.000012  gram 
NaOH  per  liter.1 

The  body  katabolism  is  continually  producing  acids,  espe- 
cially carbonic,  phosphoric  and  sulphuric  acids  (256,  259),  which 
tend  to  increase  the  acidity  of  the  blood.  These  acids  are  in 
part  neutralized  by  the  ammonia  produced  in  the  katabolism  of 
protein  (233),  but  it  has  been  shown  by  the  investigations  of 
L.  J.  Henderson  that  the  salts  of  the  blood  serum,  especially 
the  sodium  phosphates  and  bicarbonates,  play  an  important 
part  in  maintaining  its  neutrality.  They  are  present  in  such 

1  Blood  is  commonly  said  to  be  alkaline  because  it  gives  an  alkaline  reaction  to 
ordinary  indicators,  such  as  litmus.  Such  a  reaction,  however,  gives  no  definite 
measure  of  the  true  alkalinity  or  acidity. 


1 90  NUTRITION   OF   FARM   ANIMALS 

proportions  that  their  solution  possesses  nearly  the  maximum 
capacity  for  the  preservation  ol  neutrality,  while  they  also, 
particularly  the  phosphates,  serve  as  a  means  of  elimination  of 
an  excess  of  acid  through  the  kidneys  in  the  form  of  the  acid 
phosphates  of  the  urine. 

272.  Other  functions  of  ash.  —  The  three  general  functions 
just  enumerated  by  no  means  exhaust  the  list  of  offices  performed 
by  the  ash  ingredients.     Iron,  for  example,  is  an  essential  in- 
gredient of  haemoglobin,  the  coloring  matter  of  the  red  blood 
corpuscles,  which  is  the  vehicle  by  which  oxygen  is  distributed 
throughout  the  body  (191).     Although  contained  in  the  body 
in  relatively  minute  amounts,  this  element  is,  therefore,  one  of 
prime  necessity.     lodin  appears  to  be  an  essential  ingredient 
of  the   thyroid  glands,  and  although  we  are  ignorant  of  its 
exact  functions  it  is  known  that  the  absence  of  these  glands,  or 
their    failure  to  function,  gives  rise    to    serious    disturbances 
(goitre,    myxcedema).     Recent    investigations    seem    to    indi- 
cate that  manganese  and  boron,  and  perhaps  other  elements 
not    heretofore    regarded    as    essential,    may    have    important 
functions   as   catalysts   in   plants   and  perhaps,    therefore,   in 
animals  also,  although  this  is  at  present  a  conjecture.     It  is 
likewise  possible  that  other  elements  present  in  small  amounts 
may  later  be  shown  to  have  physiological  functions. 

273.  Functions  of  water.  —  Its  very  familiarity  tends  to  make 
us  overlook  the  striking  nature  of  the  fact  that  life  as  we  know 
it  is  impossible  in  the  absence  of  water.     If  protoplasm  may  be 
regarded  as  a  collodial  solution,  one  may  almost  say  that  life 
is  possible  only  in  aqueous  solutions. 

Some  reasons  for  this  are  fairly  obvious.  The  phenomena  of 
osmotic  pressure  and  ionization,  for  example,  whose  impor- 
tance has  just  been  indicated,  are  substantially  solution  phe- 
nomena. It  is  possible  also  that  there  are  more  fundamental 
reasons  for  this  striking  fact.  Certainly  the  larger  share  of  our 
present  chemical  knowledge  relates  to  the  chemistry  of  either 
aqueous  solutions  or  gases,  two  states  resembling  each  other 
in  many  respects  and  in  which  chemical  action  seems  to  occur 
most  readily,  if  indeed  it  ever  takes  place  in  the  solid  state. 
Moreover,  it  has  been  shown  that  some  reactions,  at  least,  in 
which  water  is  not  commonly  regarded  as  concerned,  are 
dependent  upon  the  presence  of  minute  amounts  of  this  sub- 


METABOLISM  191 

stance,  or  at  least  proceed  with  extreme  slowness  in  its  absence. 
Such,  for  example,  is  the  action  of  chlorin  on  metallic  copper 
or  iron,  or  of  oxygen  upon  many  of  the  elements  even  at  high 
temperatures. 

Aside  from  these  considerations,  however,  the  importance  of 
the  part  played  by  water  in  the  animal  economy  is  sufficiently 
obvious,  while  it  constitutes  in  most  cases  more  than  half  of 
the  weight  of  the  body  (97)  and  therefore  may  be  regarded 
as  having  structural  importance. 


CHAPTER  VI 

THE    BALANCE   OF   NUTRITION 

§  i.    GENERAL  CONCEPTION 

274.  The  animal  as  a  prime  motor.  —  The  living  animal 
constitutes  what  is  known  as  a  prime  motor ;  that  is,  it  gener- 
ates power  for  its  own  operation  and  is  able  to  produce  a  surplus 
which  may  be  applied  to  do  external  work.     In  particular,  a 
fairly  close  analogy  may  be  drawn  between  the  animal  body  and 
what  are  known  as  internal  combustion  motors.     In  such  motors, 
a  fuel  (gas,  gasoline,  alcohol,  etc.)  is  burned  in  the  cylinder  of 
the  engine  itself  and  its  available  chemical  energy  is  transformed 
in  part  into  motion  and  in  part  into  heat.     In  a  somewhat 
similar  manner  the  compounds  supplied  to  the  cells  of  the  body 
by  the  processes  of  digestion,  resorption  and  circulation  are 
katabolized,  combine  with  the  oxygen  introduced  through  the 
lungs,  and  yield  energy  for  the  various  activities  of  the  organism. 
It  should  be  noted  that  these  activities  include  not  merely  ex- 
ternal work  done  by  the  animal  but  likewise  a  variety  of  internal 
work,  such  as  that  of  circulation,  respiration,  digestion,  resorp- 
tion, secretion,  etc.     In  other  words,  the  animal  machine  is 
always  in  operation,  even  when  performing  no  external  work. 

275.  Expenditure  by  the  body.  —  When  in  operation,  a  me- 
chanical prime  motor  (a  gasoline  engine,  for  example)  consumes 
two  things.     First,  the  material  of  which  the  working  parts  are 
composed  is  gradually  worn  away  so  that  ultimately  repairs 
are  necessary,  and  second,  fuel  is  consumed  in  amount  depend- 
ing upon  the  work  done.     Substantially  the  same  thing  is  true 
of  the  animal  body. 

The  working  machinery  of  the  body  may  be  regarded  as 
composed  essentially  of  water,  ash  and  protein.  This  ma- 
chinery, like  that  of  the  engine,  is  continually  wearing  out ;  that 
is,  the  protein  in  particular  is  being  continually  katabolized  and 

192 


THE  BALANCE  OF  NUTRITION  1 93 

the  products  of  its  oxidation  excreted.  In  addition,  the  activi- 
ties of  the  body,  like  those  of  the  engine,  require  a  supply  of 
fuel  material  containing  available  chemical  energy  equivalent 
to  the  work  to  be  done.  For  this  purpose  the  body  utilizes 
in  the  first  instance  the  substances  contained  in  its  own  cells 
and  tissues.  As  shown  in  Chapter  V,  all  the  organic  ingredients 
of  the  body  —  protein,  fat  and  carbohydrates  —  undergo 
katabolism,  giving  rise  to  carbon  dioxid,  water  and  compara- 
tively simple  nitrogenous  products,  accompanied  by  a  trans- 
formation of  their  chemical  energy  into  other  forms.  In  other 
words,  the  body  is  a  storehouse  of  chemical  energy  as  well  as  a 
mechanism.  This  stored-up  energy  of  the  body  is  contained 
particularly  in  its  fat,  and  to  a  minor  degree  in  its  glycogen, 
while  the  body  protein,  although  it  likewise  yields  energy  when 
katabolized,  especially  through  the  oxidation  of  its  non-nitrog- 
enous residue  (229),  usually  plays  a  small  part  quantitatively. 
The  fat  of  the  body  constitutes  its  great  reserve  of  energy.  The 
store  of  reserve  material  in  the  body  may  be  compared,  for  the 
sake  of  illustration,  to  the  gasoline  in  the  tank  of  an  automobile, 
with  the  difference,  however,  that  the  body  derives  more  or 
less  energy  from  the  combustion  of  the  material  (protein)  of 
the  engine  itself. 

276.  The  feed.  —  Neither  the  automobile  nor  the  animal  can 
long  depend  entirely  upon  its  own  stock  of  material  without 
disaster.  Sooner  or  later  it  must  obtain  supplies  from  the  out- 
side. The  supplies  required  in  both  cases  are  obviously  of  two 
classes,  corresponding  to  the  two  classes  of  materials  consumed 
in  the  operation  of  the  machine,  and  may  be  briefly  designated 
as  repair  material  and  fuel. 

In  the  automobile,  parts  of  the  machinery,  the  tires,  etc.,  as 
they  wear  out  must  be  replaced  by  new  ones  of  the  same  kind, 
while  the  gasoline  tank  must  be  filled  at  intervals  and  the  work- 
ing parts  must  be  suitably  lubricated.  The  case  of  the  animal 
is  precisely  similar.  In  the  first  place,  it  must  be  supplied  in 
its  feed  with  materials  from  which,  by  the  processes  of  digestion 
and  resorption,  it  can  secure  the  particular  atomic  groupings 
(amino  acids,  peptids,  ash  ingredients,  etc.)  which  will  exactly 
fit  into  its  protoplasm  and  replace  those  eliminated  by  the  vital 
activities.  In  the  second  place  it  must  also  derive  from  its 
feed  molecules  which  it  may,  according  to  circumstances,  break 
o 


194  NUTRITION   OF   FARM   ANIMALS 

down  (katabolize)  at  once  for  the  sake  of  their  energy  or  store 
up  as  a  reserve  of  energy  (fat,  glycogen)  for  future  use.  Finally, 
to  carry  the  analogy  a  step  further,  it  must  obtain  from  its  feed 
such  amounts  and  proportions  of  the  several  ash  ingredients 
as  will  maintain  the  necessary  working  conditions  of  osmotic 
pressure,  ionic  concentration  and  the  like,  somewhat  as  the 
engine  must  be  lubricated. 

277.  Balance   of  income  and   expenditure.  —  It  is  evident 
from  the  foregoing  considerations  that  the  body  exhibits  two 
sets  of  activities,  those  concerned  in  its  actions  as  a  prime 
motor,  tending  to  destroy  it,  and  those  of  nutrition,  tending  to 
build  up  and  increase  it.     Whether  the  body  gains,  is  main- 
tained or  falls  away  depends  upon  the  balance  between  these 
two  sets  of  activities. 

In  a  broad  general  way,  of  course,  this  fact  is  perfectly  obvious. 
We  do  not  need  a  physiologist  to  teach  us  that  the  horse  or  cow 
cannot  long  continue  to  do  work  or  to  yield  milk  unless  supplied 
with  sufficient  feed  to  make  good  the  resulting  loss  of  body 
material.  Similarly,  we  are  familiar  with  the  fact  that  those 
operations  of  the  body  which  go  on  in  a  state  of  so-called  rest 
likewise  require  material  for  their  support,  so  that  the  mere 
maintenance  of  an  animal  calls  for  an  expenditure  of  feed. 
What  is  needed  in  a  scientific  study  of  nutrition  is  something 
more  than  the  mere  general  knowledge  of  these  familiar  facts ; 
namely,  a  quantitative  measure  of  the  extent  to  which  the 
various  feeding  stuffs  or  their  single  ingredients  contribute  to 
the  nutritive  functions  of  the  body  under  varying  conditions. 

§  2.    METHODS  OF  INVESTIGATION 

278.  Investigation  of  details  of  metabolism.  —  One  method 
of  attacking  the  problem  just  stated  is  by  investigating  the 
details  of  the  metabolic  processes.     In  the  study  of  metabolism 
(including  the  chemical  changes  in  digestion  and  resorption) 
the  attempt  is  made  to  follow  the  various  ingredients  of  the  feed 
through  the  body  and  to  trace  in  detail  how,  where  and  to  what 
extent  they  contribute  to  the  maintenance  or  growth  of  tissue 
or  supply  energy  for  the  use  of  the  organism.     Such  studies  are 
of  fundamental  importance.     They  reveal  to  us  how  the  animal 
mechanism   operates.     When    carried   to   their   ultimate   con- 


THE   BALANCE   OF   NUTRITION  195 

elusion,  and  when  accompanied  by  a  complete  knowledge  of 
the  chemical  ingredients  found  in  feeding  stuffs,  they  will  make 
it  possible  to  give  an  exhaustive  account  of  nutrition  as  a  physico- 
chemical  process.  It  is  hardly  necessary  to  say  that  the  reali- 
zation of  this  ideal  lies  in  the  distant  future. 

279.  Total  nutritive  effect.  —  Meanwhile,  students  of   stock 
feeding  are  interested  primarily  in  a  somewhat  different  aspect 
of  the  subject,  viz.,  in  the  aggregate  effect  of  the  varied  and  com- 
plex metabolic  processes  in  reducing,  maintaining  or  increasing 
the  stock  of  matter  and  of  chemical  energy  in  the  body.     Is  the 
body  under  any  given  regimen  maintaining  itself  and  making 
due  growth,  or  is  the  animal  doing  work  or  yielding  milk  or 
other  products  at  the  expense  of  its  own  tissues?     This  is  evi- 
dently a  question  of  balance.     Is  the  income  of  the  body  equal 
to  its  outgo  ? 

280.  The  schematic  body.  —  The  idea  of  the  organism  as 
dependent  upon  a  balance  between  constructive  and  destructive 
activities  may  be  made  more  specific  by  means  of  the  conception 
of  the  schematic  body,  which  regards  the  body  of  the  animal, 
aside  from  water,  as  consisting  essentially  of  ash,  protein  and 
fat,  together  with  an  amount  of  glycogen  so  small  that  it  may  for 
many  purposes  be  neglected. 

The  justification  for  this  conception  is  found  in  the  data  con- 
tained in  Chapter  II,  §  3,  regarding  the  composition  of  the  animal 
as  a  whole.  It  will  be  recalled  that  in  the  investigations  there 
recorded  the  water,  ash  and  fat  were  determined  directly,  the 
difference  between  the  sum  of  these  and  the  total  weight  of  the 
animal,  of  course,  showing  the  amount  of  fat-  and  ash-free  dry 
matter.  In  those  cases  in  which  the  total  nitrogen  contained 
in  the  body  was  also  determined,  it  appeared  (99)  that,  with 
one  exception,  the  percentage  of  nitrogen  in  this  fat-  and  ash-free 
dry  matter  closely  approximated  that  in  the  animal  proteins. 
In  other  words,  the  amount  of  glycogen  and  other  substances 
included  in  the  fat-  and  ash-free  dry  matter  is  so  small  as  to  be 
negligible  and  the  latter  may  be  considered  to  consist  essen- 
tially of  protein. 

From  this  point  of  view,  it  is  evident  that  the  effect  of  any 
feeding  stuff  or  ration  in  causing  a  gain  or  preventing  a  loss  of 
ash,  protein  and  fat  (and  glycogen)  shows  its  aggregate  nutri- 
tive effect.  Or,  since  the  organic  matter  of  the  body  may  be 


196  NUTRITION  OF  FARM   ANIMALS 

looked  upon  in  the  light  of  stored  energy,  a  still  simpler  ex- 
pression of  the  nutritive  effect  may  be  obtained  by  determining 
the  effect  of  the  feed  upon  the  store  of  protein  and  of  chemical 
energy  in  the  body.1 

Experiments  directed  to  the  determination  of  the  gain  or  loss 
of  matter  and  of  energy  by  the  body  have  been  of  two  general 
kinds,  viz.,  comparative  slaughter  tests  and  what  are  called 
balance  experiments.  Both  have  played  an  important  role  in 
the  study  of  nutrition. 

281.  Live  weight  as  a  measure  of  nutritive  effect.  —  At  the 
very  outset,  however,  the  question  arises  whether  the  simple 
and  obvious  method  of  weighing  an  experimental  animal  is  not 
sufficient  to  determine  the  aggregate  effect  of  a  ration,  without 
the  necessity  for  any  elaborate  experimental  devices. 

The  answer  to  this  question  depends  largely  upon  the  object 
of  the  experiment.  If  it  be  one  undertaken  to  answer  a  com- 
mercial question,  the  increase  in  live  weight  during  a  considerable 
period,  when  determined  with  the  necessary  precautions,  may 
be  entirely  adequate  as  a  measure  of  the  results  obtained.  If, 
for  example,  the  question  under  investigation  is  the  relative 
profits  of  two  methods  of  fattening  cattle,  the  gains  made  by  a 
considerable  number  of  animals,  together  with  the  judgment  of 
the  market  regarding  the  quality  of  the  finished  animals,  will 
substantially  determine  which  method  is  to  be  preferred.  The 
use  of  more  elaborate  experimental  methods  would  not  only  be 
a  needless  refinement  but  might  actually  interfere  with  the 
settlement  of  the  economic  question  involved.  So,  too,  in  the 
handling  of  young  stock  or  in  milk  production,  the  general 
appearance  and  condition  of  the  animals,  together  with  the  gain 
in  live  weight  or  the  yield  of  milk,  furnishes  a  sufficiently  ac- 
curate indication  of  the  practical  results  obtained,  provided  a 
sufficient  number  of  individuals  be  employed. 

If,  however,  the  purpose  of  the  investigation  is  to  study  some 
question  relating  to  the  fundamental  principles  of  nutrition, 

1  To  make  the  demonstration  absolutely  complete,  of  course,  it  would  be  neces- 
sary to  show  that  the  stock  of  each  different  kind  of  protein  in  the  body  had  been 
maintained  and  that  all  the  energy  containing  material  derived  from  the  feed  was 
actually  capable  of  yielding  up  its  energy  to  the  organism.  Usually,  however, 
especially  on  a  mixed  diet,  it  may  be  assumed  that  if  the  body  maintains  its  stock  of 
protein,  each  particular  kind  is  practically  maintained,  while  no  considerable  storage 
of  unavailable  energy  in  the  body  has  been  recognized. 


THE  BALANCE  OF  NUTRITION  197 

such,  for  example,  as  the  relative  values  of  the  carbohydrates 
and  fats,  the  changes  of  live  weight  are  of  little  value  as  indica- 
tors. For  this  there  are  two  principal  reasons. 

282.  Fluctuations  in  live  weight.  —  In  the  first  place  the 
live  weight  of  an  animal  fluctuates  considerably  from  day  to  day, 
even  when  taken  under  what  seem  to  be  identical  conditions, 
chiefly  on  account  of  variations  in  the  weight  of  the  contents 
of  the  digestive  tract.  This  is  true  of  all  animals,  but  especially 
of  herbivora  on  account  of  their  comparatively  bulky  feed,  and 
reaches  the  extreme  in  ruminants. 

For  example,  a  steer  which  had  been  receiving  daily  for  two 
months  a  uniform  ration  of  6.35  Kgs.  of  timothy  hay  and  which  was 
kept  under  as  uniform  conditions  as  possible  was  weighed  daily  24 
hours  after  watering.  On  February  19  he  weighed  419.0  Kgs.  and 
on  March  6  practically  the  same  amount,  418.6  Kgs.  The  inter- 
mediate weights,  however,  were  as  follows:  — 

February  19 419.0  Kgs. 

February  20 43 1 .6  Kgs. 

February  21 43i-o  Kgs. 

February  22 440.6  Kgs. 

February  23 431.2  Kgs. 

February  24 444-8  Kgs. 

February  25 427.6  Kgs. 

February  26 427.9  Kgs. 

February  27 437.8  Kgs. 

February  28 436.0  Kgs. 

March  i        437-2  Kgs. 

March  2        443-Q  Kgs. 

March  3        428.4  Kgs. 

March  4       433.4  Kgs. 

March  5       436.8  Kgs. 

March  6        418.6  Kgs. 

It  is  evident  that  conclusions  based  upon  a  comparison  of  single 
weighings  would  have  been  entirely  untrustworthy.  Thus  a  com- 
parison of  the  live  weight  of  February  19  with  that  of  March  6  would 
have  led  to  the  conclusion  that  the  animal  was  being  practically  main- 
tained. If,  however,  the  initial  weight  had  chanced  to  be  taken  on 
February  20,  a  comparison  with  that  of  March  6  would  have  shown 
a  loss  of  13  Kgs.,  while  on  the  other  hand,  a  comparison  of  February 
19  with  March  5  would  have  shown  a  gain  of  17.8  Kgs.  Even  aver- 


198  NUTRITION  OF  FARM  ANIMALS 

aging  two  or  three  successive  daily  weighings,  as  is  often  done,  while 
it  reduces  the  error  does  not  eliminate  it.  For  example,  a  comparison 
of  the  average  of  February  19-21  with  that  of  March  3-5  shows  a 
gain  of  8.7  Kgs.,  while  if  each  average  be  taken  a  day  later,  viz., 
February  20-22  and  March  4-6,  the  comparison  shows  a  loss  of  4.8 
Kgs.  By  increasing  the  number  of  single  weighings  averaged,  the 
uncertainty  may,  of  course,  be  further  reduced  but  not  entirely  elimi- 
nated, even  ten-day  averages  varying  materially,  as  is  illustrated 
by  the  following  figures. 

February  24-March  5,  inclusive,  435.3  Kgs. 
February  25-March  6,  inclusive,  432.7  Kgs. 
February  26-March  7,  inclusive,  432.6  Kgs. 
February  27-March  8,  inclusive,  434.2  Kgs. 

A  similar  reduction  of  the  error  may  be  obtained  by  the  use  of  a 
number  of  animals  combined  into  a  group  which  is  treated  as  an  in- 
dividual, the  fluctuations  in  the  single  animals  tending  to  balance 
each  other. 

These  fluctuations  are  such  as  to  preclude  the  use  of  the 
gain  in  live  weight  as  a  measure  of  the  nutritive  effect  in  exact 
scientific  investigations,  while  it  is  evident  that  they  must  also 
be  considered  in  the  planning  and  interpreting  of  commercial 
experiments,  as  well  as  in  judging  the  effects  of  rations  in  prac- 
tice. Such  experiments  should  extend  over  a  considerable 
length  of  time  and  include  a  considerable  number  of  animals, 
while  the  weights  on  which  comparisons  are  based  should  be  the 
average  of  as  many  single  weighings  as  possible. 

283.  Composition  of  increase.  —  In  the  second  place,  even 
were  it  possible  to  ascertain  the  gain  or  loss  in  weight  by  the 
body  tissues  proper,  exclusive  of  the  contents  of  the  digestive 
tract,  i.e.,  the  empty  weight,  the  composition  of  the  material 
gained  would  still  be  unknown.  An  increase  of  a  kilogram  in 
tissue  weight,  for  example,  might  consist  chiefly  of  adipose  tissue 
containing  10  or  12  per  cent  of  water  (95),  or  it  might  be  largely 
muscular  tissue  with  75  or  80  per  cent  of  water  (87).  Moreover, 
aside  from  the  difference  in  water  content,  the  dry  matter 
of  adipose  tissue  carries  more  chemical  energy  than  that  of 
muscular  tissue,  so  that  a  gain  of  a  kilogram  in  the  former 
case  would  be  equivalent  to  the  storage  of  seven  or  eight  times 
as  much  energy  as  in  the  latter.  Finally,  a  knowledge  of  the 


THE  BALANCE  OF  NUTRITION  IQQ 

kind  of  material  gained  or  lost  is  necessary.  In  the  study 
of  growth,  for  example,  it  is  important  to  know  how  much  of 
the  increase  in  weight  is  due  to  a  storage  of  protein,  ash,  etc., 
i.e.,  to  real  growth,  and  how  much  to  a  mere  storage  of  fat  or 
water,  or  both. 

For  all  these  reasons  the  increase  or  decrease  in  live  weight, 
while  not  valueless,  is  by  itself  an  entirely  inadequate  measure 
of  nutritive  effect  in  investigations  into  the  principles  of  nu- 
trition. In  such  experiments  it  is  essential  to  determine  at 
least  the  gain  or  loss  of  the  great  groups  of  substances  of  which 
the  body  is  composed,  viz.,  water,  ash,  protein,  fat  and  if  pos- 
sible carbohydrates,  by  one  of  the  two  general  methods  already 
mentioned  as  available  for  this  purpose,  viz.,  the  comparative 
slaughter  test  or  the  balance  experiment. 

284.  The  comparative  slaughter  test.  —  This  method  seeks 
to  determine  by  analysis  the  actual  weights  of  water,  protein, 
fat,  etc.,  or  the  quantities  of  chemical  energy,  contained  in  the 
body  of  the  experimental  animal  at  the  beginning  and  at  the 
end  of  the  experiment.  Since,  however,  it  is  obviously  im- 
possible to  analyze  the  same  animal  twice,  its  original  stock  of 
protein,  etc.,  is  ascertained  by  the  use  of  a  check  animal  as 
exactly  like  the  other  in  age,  weight,  condition,  conformation, 
etc.,  as  it  is  possible  to  select,  which  is  slaughtered  and  analyzed 
at  the  beginning  of  the  experiment.  Assuming  initial  identity  of 
percentage  composition  for  the  two  animals,  the  results  of  this 
analysis  are  used  to  compute  the  weights  of  the  several  ingredi- 
ents contained  in  the  body  of  the  experimental  animal  at  the 
outset  of  the  experiment,  while  the  animal  itself  is  analyzed  at 
its  close. 

The  method  of  comparative  slaughter  tests  has  the  advantage  of 
being  a  direct  determination  of  the  amounts  of  each  ingredient  gained 
and  of  requiring  comparatively  simple  appliances.  Furthermore,  it 
may  be  applied  not  only  to  the  conventional  groups  of  protein,  fat, 
etc.,  but  to  any  substance  capable  of  accurate  analytical  determina- 
tion. Finally,  in  addition  to  the  total  amount  of  any  substance,  its 
distribution  between  different  parts  of  the  body  may  be  ascertained. 
On  the  other  hand,  the  method  has  certain  drawbacks. 

In  the  first  place,  it  requires  relatively  long  experimental  periods. 
Assuming  the  work  of  weighing,  sampling  and  analysis  to  be  correctly 
performed,  the  accuracy  of  the  results  evidently  depends  upon  the 


200  NUTRITION  OF   FARM  ANIMALS 

care  and  skill  exercised  in  the  choice  of  the  check  animal.  The  as- 
sumed identity  of  composition  of  the  two  animals  cannot  in  the  nature 
of  things  be  proved  and  is  very  unlikely  to  be  absolute.  In  a  short 
experiment,  therefore,  the  error  thus  possibly  introduced  may  be  rela- 
tively large.  Its  importance  diminishes  the  greater  the  increase 
made  over  the  original  weight,  i.e.,  the  longer  the  period  covered 
by  the  experiment.  Furthermore,  an  experiment  by  this  method 
can  be  divided  into  periods  only  by  the  use  of  additional  check 
animals,  involving  additional  assumptions  as  to  identity  of  compo- 
sition at  different  times,  while  even  these  subdivisions,  for  the  reason 
just  stated,  must  be  fairly  long.  Finally,  the  method  is  labori- 
ous, especially  with  the  larger  animals.  The  different  parts  of  the 
carcass  must  be  separated,  the  weight  of  each  part  accurately  deter- 
mined, avoiding  mechanical  losses  and  making  due  allowance  for 
evaporation  of  water.  A  correct  sample  of  each  part  must  be 
taken  promptly  and  at  once  so  treated  as  to  preclude  any  changes 
previous  to  its  analysis.  The  task  of  analyzing  the  carcass  of  a 
hog  or  sheep,  and  still  more  that  of  a  steer,  with  the  degree  of 
accuracy  required  in  -a  scientific  investigation  is  not  one  to  be  un- 
dertaken lightly. 

285.  The  balance  experiment.  —  The  comparative  slaughter 
test  attempts  to  determine  the  weights  of  the  several  ingredients 
contained  in  the  body  at  two  different  times.  The  balance 
experiment,  on  the  contrary,  consists  of  a  comparison  of  in- 
come and  outgo  and  does  not  attempt  to  determine  the  original 
stock  in  the  body.  If  I  know  that  I  have  a  balance  of  $50  in 
bank  at  the  beginning  of  the  month  and  $150  at  the  end,  it  is 
clear  that  I  have  gained  $100  in  the  meantime.  This  is  the 
principle  of  the  comparative  slaughter  test.  On  the  other  hand, 
if  I  know  that  my  deposits  during  the  month  were  $500  and  my 
drafts  $400,  I  am  equally  sure  that  I  have  gained  $100,  even 
if  I  do  not  know  whether  my  balance  at  the  beginning  was  $50 
or  $500.  This  is  the  principle  of  the  balance  experiment.  If, 
for  example,  a  steer  digests  750  grams  of  protein  out  of  his  daily 
ration  and  if  the  amount  of  nitrogenous  products  excreted  in 
24  hours  shows  that  he  has  katabolized  500  grams  of  protein,  it 
is  evident  that  his  original  stock  of  protein,  whatever  its  amount 
may  have  been,  has  been  increased  by  250  grams.  By  compari- 
sons based  on  the  same  general  principle,  although  more  com- 
plicated as  to  details,  the  increase  or  decrease  of  the  body's 
stock  of  fat,  glycogen,  ash  and  water  or  of  chemical  energy  may 


THE  BALANCE  OF  NUTRITION  2OI 

be  determined.    The  specific  methods  used  for  such  comparisons 
are  described  in  the  two  following  sections. 

A  great  advantage  of  the  balance  experiment  is  the  comparatively 
short  time  which  it  requires.  A  period  sufficiently  long  for  the  deter- 
mination of  the  digestibility  of  a  ration  (159)  is  in  general  suffi- 
cient also  for  a  balance  experiment,  while  for  the  requisite  determina- 
tion of  the  respiratory  products  or  of  the  heat  produced  twenty-four 
to  forty-eight  hours  suffice,  and  even  this  short  period  may  be  divided 
into  a  number  of  subperiods  of  a  few  hours  each.  For  this  reason, 
and  also  because  the  animal  is  not  injured  in  the  process,  repeated 
experiments  may  be  made  on  the  same  subject,  so  that  the  effect  of 
various  rations  or  conditions  may  be  compared  on  the  same  individual, 
while  the  method  of  comparative  slaughter  tests  necessarily  involves 
comparisons  between  two  different  animals. 

On  the  other  hand,  the  complete  balance  experiment  requires  elab- 
orate and  expensive  apparatus,  while  opinions  as  to  the  relative 
amount  of  labbr  involved  in  the  two  classes  of  experiments  would 
perhaps  depend  largely  upon  the  previous  experience  of  the  experi- 
menter. Furthermore,  the  balance  experiment  shows  only  the  amounts 
of  the  constituent  groups  —  protein,  fat,  etc.  —  gained  or  lost.  It 
affords  no  opportunity  to  subdivide  these  and  determine  the  fate  of 
single  chemical  compounds  nor  does  it  give  any  clue  to  the  particular 
region  of  the  body  where  the  gains  have  been  deposited. 

286.  The  balance  of  nutrition.  —  The  phrase  "  balance  of  nu- 
trition "  used  as  the  title  of  this  chapter  refers  in  a  general  way  to 
the  balance  between  income  and  outgo  of  matter  and  energy  in  the 
body  as  determined  by  the  methods  of  the  balance  experiment. 

Logically,  of  course,  the  comparative  slaughter  test,  if  com- 
bined with  determinations  of  the  feed  consumed,  may  also  be 
regarded  as  a  balance  experiment.  In  it  the  income  of  the  body 
and  the  resulting  gain  are  determined,  leaving  the  outgo  to  be 
inferred,  while  in  a  balance  experiment  in  the  technical  sense, 
the  income  and  outgo  are  determined  and  the  gain  is  inferred. 
Nevertheless,  the  latter  type  of  experiment  has  played  so  large 
a  part  in  the  study  of  the  balance  of  nutrition,  both  for  physio- 
logical and  for  agricultural  purposes,  that  a  clear  conception  of 
its  methods  and  postulates  is  essential  for  a  comprehension  of 
many  of  the  results  to  be  considered  in  subsequent  chapters. 
The  subject  may  be  conveniently  considered  under  the  two 
heads  of  the  balance  of  matter  and  the  balance  of  energy. 


202  NUTRITION  OF   FARM  ANIMALS 

§  3.  THE  BALANCE  or  MATTER 
The  gain  or  loss  of  protein 

287.  The  nitrogen  balance.  —  Feed  protein  which  fails  to 
be  stored  up  in  the  body  is  not  excreted  as  protein  but  in  the 
form  of  the  various  products  of  its  katabolism.     The  gain  or 
loss  of  protein,  therefore,  cannot  be  determined  by  a  direct 
comparison  of  its  income  and  outgo  because  there  is  no  outgo 
of  protein  as  such.     Since,  however,  the  protein  of  the  schematic 
body  (280)  is  equivalent  to  total  nitrogenous  matter,  the  gain  or 
loss  of  protein  may  be  inferred  from  that  of  its  characteristic 
element,  nitrogen,  and  this  is  readily  ascertained  by  a  com- 
parison of  the  total  nitrogen  of  the  feed  with  the  total  nitrogen 
of  the  excreta,  i.e.,  by  a  determination  of  the  nitrogen  balance. 

288.  Free  nitrogen  not  excreted.  —  In  Chapter  V  (228)  it 
was  stated  that  all  the  nitrogen  of  the  protein  katabolized  is 
found  in  the  urea  and  other  organic  compounds  which  are  ex- 
creted in  the  urine.     Obviously  this  is  a  point  of  fundamental 
importance.     If  nitrogen  leaves   the  body  only  as  combined 
nitrogen  in  the  urine  and  in  the  feed  residues  and  nitrogenous 
excretory  products  found  in  the  feces,  it  is  a  comparatively 
simple  matter  to  compare  the  income  and  outgo.     If,  however, 
the  metabolic  processes  or  the  fermentations  of  the  feed  in 
the  digestive  tract  yield  also  gaseous  nitrogen,  then  the  nitrogen 
of  the  respiratory  products  must  also  be  determined,  a  task  of 
no  small  difficulty. 

The  question  of  the  excretion  of  gaseous  nitrogen  has  been 
the  subject  of  a  vast  amount  of  investigation  and  controversy. 
Substantially  two  general  methods  of  experimentation  have  been 
followed,  viz.,  a  comparison  of  the  income  and  outgo  of  com- 
bined nitrogen  and  direct  investigation  of  the  respiratory 
products,  and  the  results  of  both  have  been  in  substantial 
accord.  The  cumulative  force  of  the  great  number  of  experi- 
ments in  which  substantial  equality  between  income  and 
outgo  of  combined  nitrogen  has  been  observed  under  condi- 
tions which  precluded  the  possibility  of  any  considerable  gain  or 
loss  of  body  protein,  together  with  the  fact  that  the  very  careful 
and  accurate  investigations  of  recent  years  upon  the  respiratory 
excretion  of  free  nitrogen  have  given  negative  results,  amount  to 


THE  BALANCE  OF  NUTRITION  203 

a   demonstration  that  nitrogen  leaves  the  body  only  in  the 
combined  form  in  the  visible  excreta. 

289.  Determination  of  nitrogen  balance.  —  There  being  no 
excretion  of  gaseous  nitrogen,  a  determination  of  the  nitrogen 
balance  requires  simply  a  determination  of  the  amounts  of  this 
element  contained  in  the  feed  and  in  the  visible  excreta.    Evi- 
dently this  end  is  already  partially  attained  in  a  digestion  ex- 
periment (158).     It  is  only  necessary  in  addition  to  provide 
for  the  quantitative  collection  and  analysis  of  the  urine  and,  in 
very  accurate  experiments,  of  the  perspiration  and  of  the  epi- 
dermal excreta,  in  order  to  obtain  data  for  a  comparison  of  the 
income  and  outgo  of  nitrogen,  and  the  same  precautions  as  to 
length  of  period,  uniformity  of  feeding,  etc.,  which  are  necessary 
in  a  digestion  experiment,  suffice  also  to  render  the  results  of  a 
balance  experiment  representative. 

290.  Example  of  a  nitrogen  balance  experiment.  —  The  digestion 
experiment  with  clover  hay  used  as  an  example  in  Chapter  III  (160) 
may  serve  also  to  illustrate  the  nature  of  a  nitrogen  balance  experi- 
ment.    In  that  experiment  the  hay  consumed  daily  contained  3.144 
Kgs.  of  dry  matter  and  the  daily  feces  1.267  Kgs.,  while  the  average 
daily  weight  of  the  urine  for  g  days  was  5.449  Kgs.     Analysis  showed 
the  following  percentages  of  nitrogen :  — 

In  dry  matter  of  hay 2.271  % 

In  dry  matter  of  feces 2.240% 

In  fresh  urine 1.074% 

The  brushings  of  the  steer  (hair,  dandruff,  etc.)  were  found  to  con- 
tain 1.87  grams  of  nitrogen  per  day.  The  daily  nitrogen  balance 
may  accordingly  be  computed  as  follows,  showing  a  loss  from  the  body 
which,  of  course,  must  be  placed  in  the  income  column  to  complete  the 
balance. 

TABLE  22.  —  EXAMPLE  OF  A  NITROGEN  BALANCE 


INCOME 
Grms. 

ODTGO 
Grms. 

Nitrogen  in  hay 

71  4.O 

Nitrogen  in  feces  
Nitrogen  in  urine  
Nitrogen  in  brushings 

28.40 

5*8.50 
1.87 

Nitrogen  lost  from  body  

17-37 

88.77 

88.77 

204  NUTRITION  OF  FARM   ANIMALS 

291.  Computation  of  protein.  —  The  conception  of  the  sche- 
matic body  (280)  upon  which  balance  experiments  are  based 
regards  the  total  nitrogenous  matter  of  the  animal  as  consisting 
substantially  of  protein.  All  the  vast  number  of  other  substances 
containing  this  element  which  have  been  identified  as  constituents 
of  the  body  are  insignificant  in  amount  as  compared  with  the 
great  mass  of  protein  which  it  contains.  Accordingly,  a  gain 
or  loss  of  nitrogen  is  interpreted  as  signifying  a  gain  or  loss  of 
protein  and  the  amount  of  the  latter  may  be  computed  from 
the  former  just  as  the  protein  of  a  feeding  stuff  is  computed  from 
its  protein  nitrogen,  it  being  only  necessary  to  fix  upon  a  suitable 
factor  or  factors,  i.  e.}  to  know  the  average  percentage  of  nitrogen 
in  body  protein. 

From  the  results  of  analyses  of  entire  bodies  of  animals  cited  in 
Chapter  II,  the  average  nitrogen  content  of  the  fat-  and  ash-free  dry 
matter  was  computed  (99)  to  be :  — 

In  Lawes  and  Gilbert's  experiments .     .     .     .     16.11% 
In  Chaniewski's  experiments 16.06% 

It  is  probable  that  in  both  cases  the  supposedly  fat-free  matter 
still  contained  some  fat,  it  having  been  subsequently  shown  that 
extraction  with  ether  does  not  remove  the  last  trace's  of  it  from  ani- 
mal tissues. 

Kohler's  analyses  (88)  of  the  fat-  and  ash-free  lean  meat  of  vari- 
ous species,  after  correction  for  the  glycogen  content  of  the  horse  flesh, 
show  an  average  nitrogen  content  of  16.64  per  cent.  Since  the  material 
of  Lawes  and  Gilbert's  and  of  Chaniewski's  experiments  doubtless  in- 
cluded some  residual  fat  and  other  non-nitrogenous  substance,  and 
since  the  larger  share  of  the  protein  of  the  body  is  contained  in  the 
muscular  tissues,  it  appears  justifiable  to  regard  Kohler's  figures  as 
representing  with  substantial  accuracy  the  average  elementary  com- 
position of  body  protein  as  a  whole,  especially  since  they  are  the  results 
of  direct  analysis  while  the  others  are  derived  from  slaughter  experi- 
ments in  which  the  limits  of  error  are  somewhat  wide. 

Assuming,  on  the  basis  of  Kohler's  results,  that  average  body 
protein  contains  16.64  Per  cent  °f  nitrogen,  the  corresponding 
protein  factor  is  6.0,  and  the  gain  or  loss  of  nitrogen  observed  in 
a  nitrogen  balance  experiment  multiplied  by  this  factor  gives  the 
gain  or  loss  of  protein.  This  is,  of  course,  an  approximation, 
since  protein  is  not  the  only  nitrogenous  substance  contained 


THE   BALANCE   OF   NUTRITION  2O$ 

in  the  body  and  since  not  all  the  animal  proteins  contain 
exactly  16.67  Per  cent  °f  nitrogen,  but  the  error  involved  is 
insignificant  in  most  cases  so  far  as  it  relates  to  the  question  of 
the  balance  between  income  and  outgo. 

On  this  basis,  the  steer  in  the  foregoing  example  was  losing 
daily  17.37  X  6.0  =  104.22  grams  of  body  protein.  Evidently 
the  results  of  an  experiment  in  which  a  gain  of  nitrogen  occurs 
can  be  computed  in  precisely  the  same  way. 

The  gain  or  loss  of  fat  and  glycogen 

292.  The  carbon  balance.  —  By  a  method  quite  similar  in 
principle  to  that  just  described  for  protein,  it  is  possible  to  com- 
pute approximately  the  gain  or  loss  of  body  fat  from  the  com- 
bined income  and  outgo  of  nitrogen  and  carbon,  while  if  the 
balance  of  hydrogen  and  of  oxygen  can  also  be  determined  the 
computation  may  be  made  considerably  more  exact  and  may 
include  glycogen  also.     The  experimental  methods,  however, 
are  necessarily  much  more  elaborate  than  those  required  for  a 
simple  determination  of  the  nitrogen  balance,  since  it  is  evident 
that,  in  addition  to  the  carbon  of  the  feed  and  of  the  visible 
excreta,  it  is  necessary  to  determine  the  amount  of  this  element 
contained  in    the    gaseous   excreta,   viz.,   carbon    dioxid   and 
methane,  while  if  the  balance  of  hydrogen  and  oxygen  is  to  be 
included,  the  hydrogen  of  the  feed,  the  water  excreted  and  the 
amount  of  oxygen  taken  up  from  the  air  must  also  be  ascertained. 
An  outline  of  the  experimental  methods  employed  for  these 
purposes  is  given  in  a  succeeding  paragraph  (297),  but  at  the 
outset  it  seems  desirable  to  confine  attention  to  the  principles 
involved. 

293.  Computation  of  gain  or  loss  of  fat.  —  According  to  the 
conception  of  the  schematic  body  (280)  on  which  the  whole 
scheme  of  the  balance  experiment  is  based,  substantially  all  the 
carbon  of  the  body  is  regarded  as  existing  in  the  two  forms  of 
protein  and  fat.     Evidently  if  a  comparison  of  the  income  and 
outgo  of  carbon  shows  a  gain  of  that  element  it  can,  according 
to  the  fundamental  assumption,  have  been  only  in  one  or  the 
other  or  both  of  these  two  forms.     The  nitrogen  balance,  how- 
ever, shows  the  amount  of  protein  gained  and  the  carbon  con- 
tent of  protein  is  known.     If  the  carbon  of  the  protein  gained 


206 


NUTRITION  OF  FARM   ANIMALS 


be  subtracted  from  the  total  gain  of  carbon,  the  remainder 
can  have  been  gained  only  in  the  form  of  fat  and  the  corre-. 
spending  amount  of  this  substance  can  be  readily  computed. 

294.  Example  of  a  carbon  balance.  —  In  a  respiration  experi- 
ment on  a  steer  a  complete  statement  of  the  nitrogen  and  carbon 
balances  is  as  follows  :  — 

TABLE  23. —  NITROGEN  AND  CARBON  BALANCES  OF  A  STEER 


NITROGEN 

CARBON 

Income 
Grms. 

Outgo 
Grms. 

Income 
Grms. 

Outgo 
Grms. 

6088  grms  timothy  huv 

56.4 

2I.Q 

33-5 
32.4 
i-3 

ii.  i 

2831.7 
172.6 

1428.7 
124.2 
8.0 
1290.2 
106.6 
46.6 

400  grms.  linseed  meal  
16610  grms  feces 

4357  grms.  urine     
37  grms.  brushings       
4730  grms.  carbon  dioxid     .... 
142  grms.  methan 

Gain  by  body  

78.3 

78.3 

3004.3 

3004.3 

The  nitrogen  balance  shows  that  the  animal  gained  n.i  X  6.0  = 
66.6  grams  of  protein.  According  to  Kohler's  results  (88),  the 
average  protein  of  cattle  contains  52.54  per  cent  of  carbon.  Conse- 
quently, the  protein  gained  in  this  experiment  contained  66.6  X  -5254 
=  35.0  grams  of  carbon.  The  total  gain  of  carbon,  however,  as 
shown  by  the  carbon  balance,  was  more  than  this,  viz.,  46.6  grams,  and 
we  accordingly  have  the  following :  — 

Total  gain  of  carbon 46.6  grams 

Carbon  in  protein  gained   .     .     .     35.0  grams 
Carbon  gained  as  fat      ....     1 1.6  grams 

The  elementary  composition  of  animal  fat  was  shown  in  Chapter 
I  (34)  to  be  very  uniform,  averaging  76.5  per  cent  of  carbon.  A 
gain  of  0.765  gram  of  carbon  in  the  form  of  fat,  therefore,  is  equiva- 
lent to  a  gain  of  one  gram  of  fat  or  a  gain  of  one  gram  of  carbon  to 
1.31  grams  of  fat,  and  accordingly  the  gain  of  n.6  grams  of  carbon 
in  the  form  of  fat  shows  a  gain  by  the  animal  of  n.6  -f-  0.765,  or 
11.6  X  1.31  =  15.2  grams  of  fat.  Substantially  the  same  method  of 


THE  BALANCE  OF  NUTRITION  207 

computation  can,  of  course,  be  applied  when  there  is  a  loss  of  nitro- 
gen or  carbon  or  both.1 

295.  Gain  or  loss  of  glycogen.  —  The  only  non-nitrogenous  organic 
substance  other  than  fat  present  in  the  body  in  sufficient  amounts  to 
affect  the  foregoing  computations  is  glycogen.     It  is  generally  assumed 
that  under  reasonably  normal  conditions  of  feeding  the  glycogen  con- 
tent of  the  body  does  not  fluctuate  materially,  so  that  any  consider- 
able or  long  continued  gain  of  carbon,  other  than  that  contained  in 
protein,  is  in  the  form  of  fat.     Probably  this  is  not  equally  true  in 
the  case  of  a  loss  of  carbon,  and  in  any  case  the  results  of  computations 
like  that  of  the  preceding  paragraph  are  evidently  subject  to  a  degree 
of  uncertainty  as  regards  a  possible  gain  or  loss  of  glycogen  by  the 
body.     While  this  is  probably  not  serious  in  reasonably  long  periods 
it  may  be  relatively  important  in  short  experiments.     If,  however, 
there  can  be  added  to  the  determination  of  the  nitrogen  and  carbon 
balance  that  of  the  balances  of  hydrogen  and  oxygen  the  means  are 
afforded  for  a  more  accurate  calculation,  since  it  is  evident  that  the 
amounts  of  the  latter  two  elements,  especially  of  oxygen,  retained  in 
the  body  would  be  greater  in  the  case  of  a  storage  of  glycogen  than  in 
that  of  a  storage  of  fat  containing  the  same  amount  of  carbon.     The 
method  of  computation  is,  however,  somewhat  complicated  and  need 
not  be  gone  into  here.2 

296.  The  respiratory  quotient.  —  The  respiratory  quotient  is 
the   ratio    of  the   volume   of   carbon   dioxid   excreted   by   an 
animal  to  the  volume  of  oxygen  taken  up  during  the  same  time, 

i.e.,  it  is   '          •     The  respiratory  quotient  will  obviously 

Vol.  G£ 

vary  according  to  the  kind  of  material  which  is  being  katabo- 
lized  in  the  body.  Thus  in  the  oxidation  of  carbohydrates  each 
liter  of  oxygen  consumed  gives  rise  to  the  production  of  one 
liter  of  carbon  dioxid  and  the  respiratory  quotient  therefore 
is  i.o.  On  the  other  hand,  when  fat  is  oxidized,  a  portion  of  the 
oxygen  unites  with  the  hydrogen  of  the  fat  and  only  the  re- 
mainder is  available  for  the  production  of  carbon  dioxid.  It 
is  easy  to  compute,  therefore,  that  each  liter  of  oxygen  con- 
sumed in  the  oxidation  of  fat  will  give  rise  to  the  production  of 

1  To  avoid  errors  in  computation  it  is  convenient  to  regard  losses  in  such  compu- 
tations as  negative  gains  and  to  carry  through  the  computation  exactly  as  in  the 
above  experiment,  using  the  algebraic  sum  or  difference  in  every  instance. 

2  See  Atwater  and  Benedict,  A  Respiration  Calorimeter,  etc.,  Carnegie  Institu- 
tion of  Washington,  Publication  No.  42  (1905). 


208  NUTRITION  OF  FARM  ANIMALS 

0.7  liter  of  carbon  dioxid.  Similarly,  it  may  be  computed  that 
if  protein  of  average  composition  be  oxidized  to  urea,  carbon 
dioxid  and  water,  the  respiratory  quotient  will  be  approxi- 
mately 0.8,  although  in  reality  the  quotient  for  protein  varies 
according  to  the  nature  of  the  nitrogenous  products  formed  and 
the  amount  of  carbon  thereby  withdrawn  from  oxidation  to 
carbon  dioxid.  Ordinarily,  however,  the  proportion  of  the 
gaseous  exchange  of  the  body  due  to  the  katabolism  of  protein 
is  comparatively  small,  so  that  if,  for  example,  the  respiratory 
quotient  closely  approaches  i.o,  it  is  clear  that  the  katabolism 
must  be  chiefly  that  of  carbohydrates,  while  if,  on  the  other 
hand,  its  value  approaches  0.7,  it  is  equally  evident  that  the 
katabolism  must  be  chiefly  that  of  fat.  Values  for  the  respira- 
tory quotient  intermediate  between  these  extremes  imply  that 
the  katabolism  is  in  part  that  of  fats  (or  proteins)  and  in  part 
that  of  carbohydrates. 

The  respiratory  quotient  of  course  affords  no  information 
regarding  the  balance  between  income  and  outgo  but  its  deter- 
mination gives  valuable  information  as  to  the  nature  of  the 
material  which  is  being  katabolized  in  the  body,  particularly 
in  short  periods. 

297.  The  respiration  apparatus.  —  A  determination  of  the 
gaseous  exchange  of  an  animal,  such  as  is  necessary  in  order  to 
formulate  the  complete  balance  of  matter,  requires  the  use  of 
some  form  of  special  apparatus  known  as  a  respiration  apparatus. 

In  its  simplest  and  earliest  form  the  respiration  apparatus 
consisted  of  a  closed  chamber  of  known  capacity,  such  as  was 
used  by  Crawford,  Mayow,  Black,  Priestly,  Lavoisier  and 
others  in  their  early  experiments.  The  animal  was  placed  in 
the  hermetically  sealed  apparatus  and  the  changes  in  the  com- 
position of  the  enclosed  air  which  were  brought  about  by  its 
respiration  were  determined.  Evidently,  however,  the  method, 
while  charmingly  simple,  is  open  to  objections.  The  oxygen 
of  the  air  is  gradually  consumed,  while  the  carbon  dioxid  and 
other  products  of  respiration  accumulate.  Even  if  the  experi- 
ment be  broken  off  before  fatal  results  to  the  animal  ensue,  it 
is  made  under  varying  and  increasingly  abnormal  conditions, 
while  no  very  long  trials  are  possible. 

Two  obvious  methods  of  avoiding  this  difficulty  at  once 
suggest  themselves;  either  to  absorb  the  products  of  respira- 


THE  BALANCE  OF  NUTRITION 


2OQ 


tion  and  replace  the  oxygen  consumed  or  to  conduct  a  current 
of  air  through  the  apparatus.  Correspondingly,  two  different 
types  of  respiration  apparatus  have  been  evolved,  known  re- 
spectively as  the  closed  circuit  and  open  circuit  apparatus, 
or,  from  the  names  of  the  investigators  who  first  developed  them 
into  practicable  appliances,  as  the  Regnault-Reiset  and  the 
Pettenkofer  apparatus.  Each  of  these  two  types  may  be  sub- 
divided into  those  intended  to  determine  the  total  gaseous  ex- 
change of  an  animal  and  those  which  take  account  only  of  the 
pulmonary  exchange. 

298.   The  Regnault-Reiset  apparatus.  —  In   the  closed  cir- 
cuit, or  Regnault-Reiset  apparatus,  respiration  takes  place  in 


RESPIRATION    CHAMBER 
0  used 


FIG.  24.- 


Scheme  of  closed  circuit  respiration  apparatus.     (Atwater  and  Benedict, 
Carnegie  Institution  of  Washington,  Publication  No.  42.) 


a  confined  volume  of  air,  the  possibility  of  any  exchange  be- 
tween it  and  the  outside  atmosphere  being  carefully  guarded 
against.  By  suitable  mechanical  means  (a  blower,  for  instance) 
the  confined  air  is  kept  in  circulation  over  suitable  absorbents 
which  take  up  the  water  and  carbon  dioxid  given  off,  while 
the  oxygen  consumed  is  replaced  from  a  gasometer  or  a  cylinder 
of  the  compressed  gas.  The  general  scheme  for  such  an  ap- 
paratus is  shown  in  Fig.  24.  The  increase  in  weight  of  the'  ab- 
sorbents plus  any  increase  in  the  amount  of  carbon  dioxid  and 


2IO 


NUTRITION  OF   FARM  ANIMALS 


water  contained  in  the  air  of  the  apparatus  shows  the  amounts 
of  these  substances  produced,  while  the  amount  of  fresh  oxygen 
admitted  minus  any  increase  of  the  oxygen  contained  in  the  air 
of  the  apparatus  shows  the  quantity  of  this  element  absorbed. 


u 


Any  methane  or  hydrogen  excreted  accumulates  in  the  ap- 
paratus and  may  be  determined  by  an  analysis  of  the  contained 
air  at  the  close  of  the  experiment.  The  amount  of  nitrogen 
contained  in  the  apparatus  should,  of  course,  remain  unchanged 
if  the  apparatus  is  working  properly. 


THE   BALANCE  OF  NUTRITION 


211 


212  NUTRITION  OF  FARM  ANIMALS 

If  the  entire  respiratory  exchange  is  to  be  determined,  the 
subject  is  placed  in  the  respiration  chamber  represented  in  the 
diagram.  If  only  the  pulmonary  exchange  is  under  investi- 
gation, the  respiration  chamber  is  replaced  by  a  mask  or  mouth- 
piece or  even  by  a  suitable  cannula  inserted  in  the  trachea. 

The  original  form  of  the  Regnault-Reiset  apparatus  l  is  shown  in 
Fig.  25.  The  same  investigators  subsequently  devised  a  larger  one 
in  which  they  made  a  number  of  experiments  upon  animals  of  various 
species  including  sheep,  calves,  swine  and  fowls.  In  theory  this  is 
the  most  perfect  form  of  respiration  apparatus,  but  numerous  tech- 
nical difficulties  arise  in  its  use.  Various  later  forms  have  been  de- 
vised but  At  water  and  Benedict  2  were  the  first  to  construct  one  of  a 
size  suitable  for  man  which  was  capable  of  a  high  degree  of  accuracy. 
Quite  recently  Zuntz  3  has  constructed  a  respiration  apparatus  of 
this  type  for  experiments  on  domestic  animals,  a  section  of  which 
is  shown  in  Fig.  26,  while  for  the  determination  of  the  pulmonary 
exchange,  Benedict  4  has  devised  a  so-called  "  Universal  "  respiration 
apparatus. 

299.  The  Pettenkofer  apparatus.  —  In  the  Pettenkofer,  or 
open  circuit,  respiration  apparatus,  the  subject  breathes  in  a 
continuous  measured  current  of  atmospheric  air  whose  content 
of  water,  carbon  dioxid  and  methane  is  determined  before  and 
after  passing  the  animal,  the  difference,  of  course,  showing  how 
much  of  each  gas  the  subject  has  added.  In  an  apparatus  suit- 
able for  small  animals  the  entire  amount  of  carbon  dioxid  and 
water  in  the  incoming  and  outgoing  air  current  may  be  deter- 
mined, but  in  the  larger  forms  it  is  necessary  to  measure  the  air 
current  and  make  analyses  upon  relatively  small  samples,  so  that 
the  analytical  errors  are  multiplied  by  a  large  factor,  while  a  de- 
termination of  the  oxygen  balance  has  not  as  yet  been  found 
practicable.  The  general  scheme  of  such  an  apparatus  is  shown 
in  the  diagram,  Fig.  27.  As  in  the  case  of  the  Regnault-Reiset 
apparatus,  the  respiration  chamber  may  be  replaced  by  a  mask, 
mouthpiece  or  cannula  for  the  investigation  of  the  pulmqnary 
exchange. 


1  Ann.  de  Chem.  et  de  Physique,  3^me  Series,  26,  299. 

2  Carnegie  Institution  of  Washington,  Publication  No.  42  (1905). 
8Landw.  Jahrb.,  44  (1913),  776. 

4Deut.  Arch.  Klin.  Med.,  107  (1912),  156. 


THE  BALANCE  OF  NUTRITION 


213 


The  first  practicable  form  of  open  circuit  apparatus  was  devised 
by  Pettenkofer  **for  experiments  on  man.  Its  general  appearance  is 
shown  in  Fig.  28.  The  comparative  simplicity  of  its  operation  and 


CH+ 

OXIDIZED     ABSORBED 
FIG.  27.  —  Scheme  of  Pettenkofer  respiration  apparatus. 


the  fact  that  it  could  be  readily  built  of  any  desired  size  led  to  its 
extensive  use  in  investigations  upon  agricultural  animals,  notably  by 
Henneberg  and  Stohmann  at  Gottingen,  Stohmann  at  Leipzig  and 
G.  Kiihn  and  later  Kellner  at  Mockern. 


FIG.  28.  —  Pettenkofer  respiration  apparatus. 

Explanatory  sketch.     {Atwater,  U.  S.  Department  of  Agriculture,  Office  of  Experiment 
Stations,  Bulletin  No.  21.) 

1  Ann.  Chem.  Pharm.,  Suppl.  Bd.  II,  p.  i. 


214 


NUTRITION  OF  FARM  ANIMALS 


The  principle  of  the  Pettenkofer  apparatus  has  also  been  very 
extensively  used  for  the  investigation  of  the  pulmonary  exchange, 
especially  by  Zuntz  and  his  associates,  'to  whom  the  development  of 
this  form  is  largely  due.  Figure  30  shows  a  horse  equipped  with  a 
tracheal  cannula  for  experiments  with  this  type  of  apparatus.  Ow- 
ing to  the  fact  that  the  excretory  gases  are  not  diluted  with  many 
times  their  volume  of  air,  as  is  the  case  when  a  respiration  chamber  is 
used,  the  results  are  much  sharper  and  it  is  possible  to  determine 
the  amount  of  oxygen  consumed  as  well  as  that  of  carbon  dioxid 
given  off. 


FIG.  29.  —  The  Mockern  respiration  apparatus.     (Bailey's  Cyclopedia  of  Ameri- 
can Agriculture.) 

300.  Investigation  of  pulmonary  exchange.  —  For  many  pur- 
poses a  determination  of  the  gaseous  exchange  in  the  lungs, 
either  with  the  Regnault-Reiset  or  the  Pettenkofer  type  of 
apparatus,  is  preferable  to  determinations  of  the  total  exchange 
in  a  respiration  chamber.  The  former  method  is  especially 
adapted  for  short  experiments.  By  its  use,  it  is  possible  to 
trace  sharply  changes  in  the  amount  of  the  metabolism,  the 
respiratory  quotient,  etc.,  produced  by  the  administration  of 
feed  substances,  drugs,  etc.,  by  experimental  lesions,  and  es- 
pecially by  work,  —  changes  whose  amounts  would  often  be 
relatively  very  small  as  compared  with  the  total  excretion  for 
24  hours  as  measured  in  the  respiration  chamber  and  which, 
therefore,  if  they  did  not  escape  detection  altogether,  could  not 
be  as  accurately  determined  either  quantitatively  or  chrono- 
logically. On  the  other  hand,  it  is  impracticable  to  continue 
its  use  through  long  periods,  —  a  day,  e.g.,  —  and  since  it  takes 


THE   BALANCE   OF  NUTRITION 


215 


2l6  NUTRITION  OF   FARM   ANIMALS 

no  account  of  the  excretion  through  the  skin  and  the  alimentary 
canal,  it  is  only  by  indirect  methods  that  it  is  possible  to  com- 
pute the  total  balance  of  carbon,  hydrogen  and  oxygen  by  its 
use. 

301.  Balance  of  water  and  of  ash  ingredients.  —  The  res- 
piration apparatus  of  either  type  serves  to  determine  the  ex- 
cretion of  water  vapor  by  the  subject  as  well  as  that  of  carbon 
dioxid  and  other  gases  and  thus,  in  connection  with  the  neces- 
sary analyses  of  the  feed  and  visible  excreta,  to  establish  the 
gain  or  loss  of  hydrogen.     Unfortunately,  more  or  less  difficulty 
is  experienced  in  determining  accurately  the  hydrogen  balance 
owing  in  part  to  the  liability  to  condensation  of  water  in  the 
apparatus  and  in  part  to  the  fact  that  the  amount  of  organic 
hydrogen  actually  entering  into  the  metabolism  of  the  animal 
is  small  as  compared  with  the  amounts  of  water  consumed  and 
simply  evaporated  again. 

The  ash  ingredients,  of  course,  with  the  possible  exception 
of  minute  amounts  of  sulphur,  all  leave  the  animal  in  the  visible 
excreta  and  the  balance  of  these  elements  may  therefore  be 
determined  according  to  the  same  principles  as  the  balance  of 
nitrogen. 

§  4.  THE  BALANCE  OF  ENERGY 

302.  Balance    of    nutrition    includes    energy.  —  Since    the 
animal  body  is  essentially  a  transformer  of  energy  (207),  the 
balance  of  nutrition  is  not  only  concerned  with  the  income  and 
outgo  of  matter  but  also,  corresponding  to  the  dual  function  of 
feed  (263),  with  the  gain  or  loss  of  energy  by  the  body.     The 
study  of  the  balance  of  energy  is  a  method  of  investigating 
some  of  the  important  problems  of  nutrition  which  has  been 
especially  developed  in  recent  years  and  which  has  proved 
fruitful   of   results.     Before   entering   upon   its   consideration, 
however,  a  brief  review  of  some  of  the  elementary  concepts  of 
energetics  as  related  to  physiological  processes  may  not  prove 
superfluous. 

Elementary  principles 

303.  Energy.  —  Up  to  this  point  the  word  energy  has  been 
used  without  any  precise  definition.     In  a  specific  study  of  the 


THE  BALANCE  OF  NUTRITION  217 

balance  of  energy,  however,  it  is  important  to  have  as  definite 
a  conception  as  possible  of  what  is  meant  by  the  term.  It  is 
not  altogether  easy  to  give  a  simple  general  definition  of  energy, 
but  for  the  present  purpose  that  given  by  Noyes  l  may  be 
adopted,  viz.,  "  That  which  gives  rise  to  changes  in  the  prop- 
erties of  bodies  and  to  the  power  to  produce  such  changes." 
For  the  present  purpose,  however,  the  conception  of  energy  may 
be  more  readily  apprehended  from  illustrations  than  from  defi- 
nitions. 

The  subject  may  be  conveniently  approached  from  the  side 
of  mechanics.  A  moving  body  is  capable  of  producing  certain 
effects  by  virtue  of  its  motion.  The  falling  weight  of  a  pile 
driver,  for  example,  forces  the  pile  downward  against  the  re- 
sistance of  the  ground  and  at  the  same  time  produces  heat  at 
the  point  of  impact.  The  projectile  fired  from  a  sixteen  inch 
gun  striking  the  side  of  the  armored  ship  overcomes  the  cohesive 
force  of  the  armor  plate  and  deforms  or  penetrates  it,  while 
the  blow  also  gives  rise  to  an  evolution  of  heat.  The  blows  of 
the  blacksmith,  if  rapid  and  heavy  enough,  may  raise  the  iron 
on  his  anvil  to  a  red  heat.  Accordingly,  it  is  said  that  a  moving 
body  possesses  energy  in  the  form  called  kinetic  energy,  or  energy 
of  motion. 

If  a  body  suspended  above  the  earth  is  set  free  it  falls  to  the 
ground,  and  at  the  moment  of  contact  with  the  earth  possesses 
a  certain  amount  of  kinetic  energy  which  was  generated  during 
its  fall  from  something  which  was  not  energy  of  motion.  This 
other  form  of  energy,  which  the  body  possessed  previous  to 
its  fall  by  virtue  of  its  position,  may  be  called  gravitation  energy. 
The  same  relation  is  illustrated  by  a  swinging  pendulum.  Dur- 
ing the  downward  swing,  the  gravitation  energy  which  it  pos- 
sessed when  at  its  highest  point  is  converted  into  kinetic  energy, 
while  when  it  rises  the  kinetic  energy  which  it  possesses  is  re- 
converted into  gravitation  energy.  When  we  lift  a  weight  we  are 
conscious  of  expending  work,  which  is  stored  up  as  gravitation 
energy,  to  be  liberated  again  as  kinetic  energy  when  the  weight 
falls. 

304.  Forms  of  energy.  —  In  general,  whenever  the  rate  of 
motion  of  a  body  is  increased  (or,  to  use  a  more  familiar  if  less 
accurate  expression,  whenever  motion  is  produced)  it  is  to  be 

1  General  Principles  of  Physical  Science,  1902. 


2l8  NUTRITION  OF   FARM   ANIMALS 

inferred,  as  in  the  case  of  the  falling  body  or  the  pendulum,  that 
the  kinetic  energy  produced  has  been  derived  from  some  other 
form  of  energy.  In  the  examples  thus  far  given  this  other  form 
of  energy  was  gravitation  energy.  In  many  familiar  instances, 
however,  this  is  not  the  case.  The  expanding  steam  in  the 
cylinder  of  a  steam  engine  parts  with  some  of  its  heat  to  produce 
the  motion  of  the  piston.  The  electric  current  in  the  wire  sets 
the  armature  of  the  motor  in  revolution.  The  combustion  of 
gasoline  in  the  cylinder  of  an  engine  produces  motion  of  the 
engine  as  well  as  heat.  Heat,  electricity  and  chemical  action 
may  all  be  sources  of  kinetic  energy  and  therefore  the  existence 
of  heat  energy,  electrical  energy  and  chemical  energy  is  inferred. 
The  manifestations  of  energy  are  of  the  most  varied  charac- 
ter but  its  forms  may  be  conveniently  grouped  under  the  fol- 
lowing general  heads :  — 

1.  Kinetic  energy  6.  Magnetic  energy 

2.  Gravitation  energy  7.  Chemical  energy 

3.  Cohesion  energy  8.  Heat  energy 

4.  Volume  energy  9.  Radiant  energy 

5.  Electrical  energy 

Of  these,  kinetic  energy,  chemical  energy  and  heat  energy 
are  those  of  most  importance  in  considering  the  balance  of  en- 
ergy in  the  animal  body. 

305.  Transformations  of  energy.  —  As  is  illustrated  by  the 
examples  given  in  the  previous  paragraphs,  and  as  has  been 
assumed  in  speaking  of  energy  changes  in  the  animal  body,  the 
various  forms  of  energy  are  capable  of  mutual  transformations. 
Heat  may  be  converted  into  motion  in  the  heat  engine.  Motion 
in  turn  is  converted  into  heat  when  a  moving  body  is  retarded 
by  friction  or  stopped  by  contact  with  another  body.  When 
gasoline  is  burned  freely,  its  chemical  energy  is  converted  into 
heat,  but  when  it  is  exploded  in  the  cylinder  of  an  engine  it 
yields  also  motion.  This  motion  in  turn  may  be  stored  in  the 
form  of  gravitation  energy  in  a  lifted  weight,  or  as  cohesion 
energy  in  a  coiled  spring,  or  it  may  be  made  a  source  of  elec- 
trical-energy which  in  its  turn  gives  rise  to  the  radiant  energy 
of  light  in  the  filament  of  a  lamp. 

In  brief,  all  the  physical  phenomena  of  the  universe  of  which 
we  can  take  cognizance  can  be  described  in  terms  of  changes  of 


THE  BALANCE  OF  NUTRITION  2IQ 

energy  either  as  to  form  or  intensity,  and  this  fact  has  led  some 
physicists  to  identify  the  concepts  of  matter  and  energy  and  to 
maintain  that  the  former  can  be  fully  interpreted  in  terms  of 
the  latter.  Without  entering  here  into  this  debated  question, 
it  will  be  convenient  to  follow  for  our  present  purpose  the  more 
familiar  course  of  regarding  matter  and  energy  as  two  distinct 
although  indissolubly  connected  entities. 

306.  The  conservation  of  energy.  —  When  a  unit  of  kinetic 
energy  is  converted  into  heat  energy  it  is  found  that  the  amount 
of  heat  obtained  is  always  the  same  no  matter  what  the  process 
employed  in  effecting  the  conversion.  Similarly,  if  a  unit  of 
heat  be  converted  into  kinetic  energy  the  amount  of  the  latter 
obtained  is  always  the  same  and  moreover  is  always  equal  to 
the  quantity  of  kinetic  energy  which  disappears  when  one  unit 
of  heat  is  produced. 

What  is  true  of  heat  energy  and  kinetic  energy  in  this  respect 
has  been  shown  to  be  true  of  all  the  forms  of  energy.  Not  only 
are  they  convertible  into  each  other  but  there  is  no  loss  or  gain 
of  energy  in  the  conversion.  When  a  quantity  of  energy  of  one 
form  disappears  an  equivalent  quantity  simultaneously  appears 
somewhere  in  some  other  form  or  forms.  This  great  generali- 
zation, perhaps  the  most  important  in  the  history  of  physical 
science,  is  known  as  the  law  of  the  conservation  of  energy,  or 
the  first  law  of  energetics.  It  was  first  clearly  and  distinctly 
formulated  by  Mayer  in  1842  and  since  that  time  has  been 
verified  by  a  great  number  of  the  most  exact  experiments  and 
forms  the  basis  of  modern  conceptions  of  physical  processes. 
In  substance,  it  asserts  that  the  total  energy  of  the  universe 
as  far  as  man  knows  it  is  a  constant  quantity,  subject  to  con- 
tinual changes  of  form  but  neither  created  nor  destroyed. 

That  the  law  of  the  conservation  of  energy  applies  to  the 
processes  taking  place  in  the  body  of  the  animal  was  exceedingly 
probable,  a  priori,  and  has  been  demonstrated  experimentally 
by  the  researches  of  Rubner  upon  dogs,  of  Laulanie  on  various 
animals,  of  Atwater,  Benedict,  Lusk  and  their  associates  upon 
men  and  of  Armsby  and  Fries  upon  cattle.1  The  impor- 
tance of  this  fact  in  relation  to  the  study  of  energy  changes  in 
the  body  is  obvious. 

1  Compare  the  writer's  Principles  of  Animal  Nutrition,  pp.  263-268  and  Penna. 
Expt.  Sta.,  Bui.  126. 


220  NUTRITION   OF   FARM   ANIMALS 

307.  Heat   energy   unique.  —  In   one   respect   heat   energy 
occupies  a  peculiar  position.     Other  forms  of  energy  are  in 
general  readily  and  completely  transformed  into  heat  but  there  is 
no  known  method  by  which  heat  can  be  completely  transformed 
into  other  forms,  such  as  kinetic  energy.     Whatever  portion  of 
the  heat  is  thus  transformed  obeys  the  law  of  the  conservation 
of  energy  but  part  of  it  always  remains  in  the  form  of  heat.1 

308.  Units  of  energy.  —  Quantities  of  energy  are  measured 
by  converting  them  into  the  same  form  and  comparing  them 
with  some  quantity  of  the  same  form  of  energy  arbitrarily  as- 
sumed as  a  unit. 

Since  quantities  of  kinetic  energy  can  be  expressed  in  terms 
of  mass,  space  and  time,  a  unit  based  on  these  concepts  is  taken 
as  the  fundamental  unit  of  energy.  The  so-called  C.  G.  S. 
(centimeter-gram-second)  unit  is  the  erg.  An  erg  is  a  quantity 
of  energy  equal  to  twice  the  kinetic  energy  possessed  by  a  mass 
of  one  gram  moving  with  a  velocity  of  one  centimeter  per  second. 
Since  this  is  a  very  small  quantity,  a  unit  called  the  joule,  equal 
to  ten  million  ergs,  is  often  employed  in  practical  measurements 
of  energy,  that  is,  i  joule  =  io7  ergs.  For  purposes  where  a  still 
larger  unit  is  desired  the  kilo-joule  equal  to  one  thousand  joules 
is  also  employed. 

In  practice,  however,  heat  is  the  form  of  energy  which  gen- 
erally lends  itself  most  readily  to  exact  determination  and, 
since  other  forms  of  energy  are  easily  converted  into  heat,  units 
of  heat  are  extensively  employed  in  the  study  of  energy.  The 
most  common  unit  for  this  purpose  is  the  calorie,  which  is  the 
quantity  of  heat  required  to  raise  the  temperature  of  one  gram 
of  water  one  degree  centigrade.2 

The  foregoing  is  known  as  the  small,  or  gram  calorie  (cal.). 
Where  larger  quantities  of  heat  are  to  be  measured  the  large, 

1  This  is,  of  course,  one  aspect  of  the  second  law  of  energetics.     Theoretically, 
a  perfect  heat  engine  with  a  lower  temperature  limit  of  absolute  zero  would  convert 
heat  completely  into  kinetic  energy.     Since,  however,  we  can  neither  obtain  the 
temperature  of  absolute  zero  nor  construct  a  perfect  heat  engine,  this  theoretical 
conception  is  simply  a  limit  which  may  be  more  or  less  remotely  approached  in 
practice  but  never  attained. 

2  Since  the  specific  heat  of  water  varies  at  different  temperatures,  an  exact  defini- 
tion of  the  calorie  must  specify  the  temperature  at  which  it  is  measured.     Practice 
differs  in  this  respect  but  the  preferable  unit  is  the  mean  calorie,  which  is  one  one- 
hundredth  of  the  amount  of  heat  required  to  raise  the  temperature  of  one  gram  of 
water  from  o°  to  100°  C. 


THE  BALANCE  OF  NUTRITION 


221 


or  kilogram  calorie  (Cal.),  equal  to  one  thousand  small  calories, 
is  employed,  while  for  still  larger  quantities  the  Therm,  equal 
to  one  thousand  large  calories,  may  be  used.  In  the  following 
pages  the  term  calorie  signifies  the  large,  or  kilogram,  calorie, 
unless  the  contrary  is  expressly  stated. 

Certain  units  of  gravitation  energy  are  also  frequently  used, 
especially  in  mechanics,  the  more  important  ones  being  the 
gram  meter,  the  kilogram  meter  and  the  foot  pound.  The 
gram  meter  is  the  energy  required  to  raise  a  weight  of  one  gram 
vertically  through  one  meter  in  opposition  to  gravity,  the  kilo- 
gram meter  is  the  energy  required  to  raise  a  weight  of  one  kilo- 
gram through  one  meter,  and  the  foot  pound  is  the  energy  re- 
quired to  raise  a  weight  of  one  pound  through  one  foot.  Since 
the  force  of  gravity  varies  at  different  points  on  the  earth's 
surface  these  units  as  thus  defined  are  not  invariable.  Taking  the 
average  force  of  gravity  at  sea  level,  however,  as  equal  to  980.5 
dynes,  the  relations  between  these  various  units  are  as  follows : 

EQUIVALENCE   OF  UNITS   OF  ENERGY 


ERGS 

GRAM 

METERS 

KILOGRAM 
METERS 

FOOT 
POUNDS 

GRAM 
CALO- 
RIES 

KILOGRAM 
CALORIES 

gram  meter  .     . 

980.5  X  10* 

O.OOI 

0.007236 

0.002344 

0.2344X  io-6 

kilogram  meter 

980.5  X  io5 

IOOO 

7.236 

2-344 

0.002344 

foot  pound  .     . 

135-5  Xio5 

138.2 

0.1382 

0.3239 

0.000324 

calorie      .     .     . 

4.184X107 

426.6 

0.4266 

3.087 

O.OOI 

Calorie    .     .     . 

4.184X10!° 

426600 

426.6 

3087 

IOOO 

309.  Measurement  of  heat  energy.  —  Quantities  of  heat 
are  measured  chiefly  in  two  ways,  viz.,  by  their  effects  in  raising 
the  temperature  of  some  substance  or  in  changing  its  state  of 
aggregation.  Instruments  for  measuring  quantities  of  heat 
are  called  calorimeters,  i.e.,  heat  measurers. 

In  the  first  method,  as  already  implied  in  the  definition  of  the 
calorie  (308),  water  is  ordinarily  used  as  the  calorimetric  sub- 
stance.1 For  example,  if  the  quantity  of  heat  to  be  measured 
can  be  transferred  without  loss  to  a  kilogram  of  water,  and  if 
the  temperature  of  the  water  is  thereby  raised  2°  C.,  it  is  evi- 
dent that  the  quantity  of  heat  imparted  to  it  is  two  large  calo- 

1  Other  substances  than  water  may,  of  course,  be  employed,  but  water  is  usually 
the  most  convenient. 


222  NUTRITION  OF   FARM   ANIMALS 

ries.  A  calorimeter  constructed  after  this  principle  is  a  water 
calorimeter.  Such  calorimeters  have  been  devised  in  a  great 
variety  of  forms  according  to  the  special  purpose  in  view.  The 
two  essential  requirements  are  that  any  escape  of  heat  by  con- 
duction or  radiation  shall  be  either  preventable  or  measurable 
and  that  the  temperature  increase  be  accurately  determined. 

In  the  second  method  the  heat  is  caused  to  expend  itself  in 
changing  the  physical  state  of  some  substance  as,  for  example, 
in  melting  ice  or  in  evaporating  some  volatile  liquid.  The  ice 


FIG.  31.  —  Lavoisier's  ice  calorimeter.     (Schaefer,  Text  Book  of  Physiology.) 

calorimeter  is  one  of  the  oldest  forms  of  calorimeter  and  has  been 
extensively  used  for  certain  classes  of  work.  Figure  31  shows  a 
simple  form  of  ice  calorimeter  used  by  Lavoisier.  The  source 
of  heat  is  placed  in  the  central  vessel  and  imparts  its  heat  to 
the  surrounding  ice,  while  the  access  of  any  extraneous  heat  is 
prevented  by  the  outside  jacket  of  ice. 

In  Lavoisier's  calorimeter  the  amount  of  ice  melted  was  determined 
by  collecting  and  weighing  the  resulting  water,  but  a  much  more 
accurate  method  of  measurement  is  based  upon  the  contraction  which 
ice  undergoes  when  converted  into  water. 


THE   BALANCE  OF  NUTRITION  223 

By  means  of  the  water  calorimeter,  it  has  been. determined 
that  the  conversion  of  one  gram  of  ice  at  o°  C.  into  liquid  water 
at  the  same  temperature  requires  79.24  gram  calories  of  heat. 
By  the  use  of  this  factor  the  indications  of  the  ice  calorimeter 
can  be  converted  into  calories. 

310.  Heats  of  Combustion.  —  As  related   to  nutrition  in- 
vestigations, the  chemical  energy  of  an  organic  substance  is 
most  commonly  measured  by  converting  it  into  heat  by  complete 
combustion  with  oxygen  and  measuring  the  heat  by  one  of  the 
methods  just  indicated,  the  result  being  called  the  heat  of  com- 
bustion of  the  substance.     In  the  method  most  commonly  used 
in  nutrition  investigations,  the  substance  is  burned  in  highly 
compressed  oxygen   (about  25  atmospheres)   in  a  lined  steel 
bomb,  the  heat  being  taken  up  by  water.     The  method  was 
first  devised  by  Berthelot  and  subsequently  modified  by  Mahler, 
Hempel  and  Atwater.     One  form  of  this  calorimeter  is  shown 
in  section  in  Fig.  32. 

311.  Heats  of  combustion  do  not  measure  total  energy.  — 
It  should  be  clearly  understood  that  the  heat  of  combustion  of 
an  organic  compound  does  not,  as  is  sometimes  erroneously 
stated,  measure  its  total  energy  but  simply  the  amount  mani- 
fested in  a  particular  chemical  change.     Thus,  in  the  complete 
oxidation  of  one  gram  of  starch  to  gaseous  carbon  dioxid  and 
liquid  water  4183  gram  calories  of  energy  are  transformed  into 
heat.     How  much  additional  energy  is  still  contained  in  the 
resulting  carbon  dioxid  and  water  we  do  not  know,  nor  is  it 
necessary  that  we  should.     In  using  the  heat  of  combustion  as 
a  measure  of  the  chemical  energy  of  starch  the  possible  energy 
content  of  the  carbon  dioxid  and  water  is  simply  assumed  as 
an  arbitrary  zero,  much  as  the  engineer  may  assume  a  datum 
plane  for  his  levels  without  regard  to  its  height  above  sea  level. 
In  other  words,  the  heat  of  combustion  of  starch  or  of  any  other 
substance  shows  how  much  chemical  energy  can  be  secured 
from  it  for  conversion  into  other  forms  by  processes  of  oxidation 
such  as  occur  in  the  body. 

312.  Law  of  initial  and  final  states.  —  In  view  of  the  very 
complicated  nature  of  the  metabolic  processes,  the  question 
naturally  arises  whether  the  amount  of  chemical  energy  which 
a  feed  ingredient  such  as  starch  really  puts  at  the  disposal  of 
the  organism  is  the  same  as  the  amount  of  chemical  energy  which 


224 


NUTRITION   OF   FARM   ANIMALS 


'  '  i.  ,•     ":.       .  '   ..   .     '.:; 


J/IG.  32.  —  Section  of  bomb  calorimeter.     (Atwater,  U.  S.  Department  of  Agri- 
culture, Office  of  Experiment  Stations,  Bulletin  No.  21.) 


THE  BALANCE  OF  NUTRITION  225 

is  transformed  into  heat  by  its  almost  instantaneous  burning 
in  oxygen.  The  answer  to  this  question  is  found  in  what  is 
called  the  law  of  initial  and  final  states. 

This  law  is  that  in  any  independent  system  the  amount  of 
energy  transformed  during  a  change  in  the  system  depends 
solely  upon  the  initial  and  final  states  of  the  system  and  not 
at  all  upon  the  rapidity  of  the  transformation  nor  upon  the  kind 
or  number  of  the  intermediate  stages  through  which  it  passes. 
Although  this  law  is  true  in  the  general  form  here  stated,  it  was 
originally  propounded  as  related  to  chemical  reactions.  If  we 
start  with  starch  and  oxygen  and  end  with  the  corresponding 
quantities  of  carbon  dioxid  and  water,  the  amount  of  chemical 
energy  converted  into  heat  or  other  forms  is  the  same,  no  matter 
whether  the  starch  be  burned  almost  instantaneously  in  pure 
oxygen  or  whether  it  be  subjected  to  slow  oxidation  in  the  tissues 
of  a  plant  buried  in  the  soil ;  whether  carbon  dioxid  and  water 
are  the  immediate  products  of  the  action  or  whether  the  starch 
passes  through  intermediate  stages  like  maltose,  glycogen, 
dextrose,  lactic  acid,  etc.,  etc.,  as  in  the  body  of  the  animal.  It 
is  simply  necessary  to  determine  the  difference  in  chemical 
energy  between  the  system  in  its  initial  and  in  its  final  state 
to  obtain  the  amount  of  energy  transformed  during  the 
change. 

313.  Measurement  of  kinetic  energy.  —  The  most  common 
method  of  measuring  the  energy  liberated  by  a  machine  or  an 
animal  as  motion  energy  is  its  conversion,  actually  or  virtually, 
into  gravitation  energy,  which  is  measured  by  the  units  given 
on  a  previous  page  (308).  In  case  of  small  amounts  of  energy 
a  weight  may  be  actually  lifted,  the  product  of  weight  into 
distance  giving  the  number  of  gram  centimeters  or  foot  pounds 
of  energy  expended.  In  other  cases,  the  subject  may  pull 
against  a  resistance  produced,  for  example,  by  the  friction  of  a 
brake,  the  traction  being  measured  by  some  form  of  spring 
balance.  In  this  case  the  kinetic  energy  is,  as  a  matter  of  fact, 
converted  into  heat,  but  the  tractive  pull  multiplied  by  the 
distance  gives  the  equivalent  number  of  gravitation  units.  In 
still  another  form  the  subject  virtually  lifts  his  own  weight  by 
climbing  the  inclined  plane  of  a  tread  power,  the  body  weight 
multiplied  by  the  distance  multiplied  by  the  sine  of  the  angle 
of  ascent  equaling  the  units  of  gravitation  energy  to  be  measured. 
Q 


226 


NUTRITION   OF   FARM   ANIMALS 


Figure  33  shows  a  form  of  this  apparatus  used  by  Zuntz  for 

work  experiments  upon  horses. 

Another  method  for  measuring  kinetic  energy  consists  in 

converting  it  into  electrical  energy  by  causing  the  subject  to 

work  against  the  resistance 
of  a  magnetic  field.  The 
amount  of  current  thus  gen- 
erated can  be  measured  in 
electrical  units,  or,  as  has 
been  done  by  Atwater,  Bene- 

Idict  and  others,  the  electrical 
energy  may  be  converted  into 
heat  and  measured  in  calories. 


The  body's  income  of  energy. 
—  Gross  energy 

314.  Only  chemical  energy 
can  be  utilized.  —  As  was 
stated  in  the  introductory 
paragraphs  of  this  chapter, 
the  animal  body  resembles  an 
internal  combustion  motor  in 
being  a  mechanism  for  the 
conversion  of  the  chemical 
energy  of  certain  compounds 
contained  in  the  feed  into 
kinetic  energy.  In  consider- 
ing the  balance  between  in- 
come and  outgo  of  energy,  it 
is  essential  to  recognize  a 
further  point  of  resemblance, 
viz.,  that  neither  the  animal 
nor  the  motor  can  utilize 
other  than  chemical  energy. 
There  is  no  evidence  that  the 
animal  body  can  use  in  any 
way  any  of  the  other  forms 
of  energy,  such  as  heat,  elec- 
tricity or  solar  radiation 


THE  BALANCE  OF  NUTRITION  227 

which  reach  it  from  its  environment,  any  more  than  the  gasoline 
engine  can  use  the  energy  of  falling  water  or  of  an  electric  cur- 
rent. Chemical  energy  is  not  merely  a  source  but  the  only  source 
from  which  the  animal  body  can  derive  its  supply. 

315.  Gross  energy.  —  The  income  of  energy  may  be  ascer- 
tained,  therefore,  by  determining    the  chemical    energy  con- 
tained in  the  various  compounds  present  in  the  feed  in  the 
manner  already  indicated  (309),  viz.,  by  converting  it  into  heat 
and  measuring  the  amount  of  the  latter  by  means  of  a  suitable 
calorimeter.     In  other  words,  the  income  of  chemical  energy  is 
measured  by  the  heat  of  combustion  of  the  feed.     In  order  to 
avoid  the  implication  that  this  is  the  total  amount  of  energy 
associated  with  the  feed  (311),  it  will  be  convenient  to  use  the 
term  gross  energy  as  equivalent  to  the  amount  of  energy  mani- 
fested as  heat  when  the  feed  is  completely  oxidized. 

Since  the  chemical  energy  of  a  feeding  stuff  is  converted  into 
heat  for  purposes  of  measurement,  its  amount  is  usually  ex- 
pressed in  heat  units.  It  should  be  clearly  understood,  however, 
that  this  is  simply  a  matter  of  convenience  and  that  it  is  the 
chemical  energy  of  feeding  stuffs  and  not  the  heat  produced  by 
their  combustion  which  is  of  use  to  the  animal. 

It  is  scarcely  necessary  to  point  out  that  the  gross  energy  of 
the  feed  does  not  measure  its  nutritive  value.  Otherwise, 
anthracite  coal,  with  a  heat  of  combustion  of  some  7.9  Cals. 
per  gram,  would  outrank  most  feeding  stuffs,  while  hydrogen 
gas,  with  a  heat  of  combustion  of  more  than  34  Cals.  per  gram 
would  stand  still  higher  in  the  list.  Obviously,  the  feed  value 
of  a  substance  depends  not  only  upon  its  content  of  gross  energy 
but  upon  the  proportion  of  the  latter  which  the  body  can 
utilize. 

316.  Heats  of  combustion.  —  The  heats  of  combustion  of  a 
great  variety   of   organic   substances   have   been   determined. 
Atwater  l  in  1895  published  a  compilation  of  results  upon  a 
large  number  of  compounds  of  importance  in  nutrition,  Fries  2 
has  prepared  a  rather  more  extensive  list,  and  Benedict  and 
Osborne 3  have  determined  the  heats  of  combustion  of  nineteen 
vegetable  proteins. 

1  U.  S.  Dept.  Agr.,  Office  Expt.  Stas.,  Bull.  21  (1895). 

2  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  94  (1907). 

3  Jour.  Biol.  Chem.,  3  (1907),  119. 


228 


NUTRITION  OF  FARM  ANIMALS 


The  following  tabulation  may  serve  to  give  a  general  idea  of 
the  gross  energy  of  some  of  the  more  important  substances 
concerned  in  nutrition.  It  should  be  specially  noted  that  the 
figures  given  are  in  most  instances  simply  approximate  averages. 

TABLE  24.  —  APPROXIMATE  GROSS  ENERGY 


PER  KILO- 
GRAM 

PER  100 
POUNDS 

Animal  protein 

Cals. 

C7OO 

Therms 
258  6 

Vegetable  protein     

<;6^6 

2ce  7 

Carbohydrates 

4.18=; 

189  8 

Sucrose 

2QC  C 

I7Q  4. 

Animal  fats     

0<OO 

4.30.0 

Butter  fat 

92OO 

4.17  3 

Vegetable  fats 

Q4.7O 

AVQ  6 

Ether  extracts  of  seeds      
Ether  extracts  of  roughages  

9467 
7962 

429.4 
361.2 

The  following  examples  taken  from  the  work  of  Kellner  and  of 
Armsby  and  Fries  will  serve  to  give  a  general  idea  of  the  gross 
energy  of  common  feeding  stuffs.  It  will  be  observed  that  the 
range  of  variation  is  relatively  small  in  most  instances. 


TABLE  25.  —  GROSS  ENERGY  OF  FEEDING  STUFFS 


PER  KILO- 
GRAM 

PER  100 
POUNDS 

Roughage 
Timothy  hay                                  

Cals. 
4.ri8 

Therms. 

204.04 

Red  clover  hay  
Miixed  hay 

4462 

4.3Q3 

202.04 
IQQ  27 

Alfalfa  hay  
Meadow  hay  
Corn  stover 

4372 

4433 

4332 

198.31 
201.08 
106.^0 

Oat  straw  

\Vheat  straw  .  ... 

4436 

44-44 

2OI.22 
201.58 

Straw  pulp  

4147 

188.11 

THE  BALANCE  OF  NUTRITION 


229 


PER  KILO- 
GRAM 

PER  100 
POUNDS 

Concentrates  " 
Corn  meal  

Cals. 
4.44.2 

Therms. 
20  1  40 

Hominy  chop 

4.7OQ 

213  60 

Wheat  bran      

4C32 

2O^  ^7    ' 

Grain  mixture  No.  ia    
Grain  mixture  No.  2b 

4685 

<l6OQ 

212.51 
2O9  06 

Beet  molasses       
Starch 

3743 

41  ^2 

169.80 

188  iz 

Peanut  oil   

041:7 

420  OO 

Wheat  gluten  

5579 

253-10 

a. Wheat  bran,  14.28  per  cent;  corn  meal,  42.86  per  cent;  old  process  linseed 
meal,  42.86  per  cent. 

b.  Corn  meal,  60  per  cent ;  crushed  oats,  30  per  cent ;  old  process  linseed  meal, 
10  per  cent. 

Some  data  are  also  available  regarding  the  gross  energy  of  the 
digested  nutrients  of  feeding  stuffs.  The  following  averages  are 
derived  chiefly  from  Kellner's  investigations. 

TABLE  26.  —  GROSS  ENERGY  OF  DIGESTED  NUTRIENTS 


PER  KILO- 
GRAM 

PER  100 
POUNDS 

Protein  of  wheat  gluten 

Cals. 
^07  ^ 

Therms. 
271  O 

Protein  —  assumed  average  

^7OO 

2<c8  6 

Crude  fiber     

42^4 

IQ^.O 

Nitrogen-free  extract  of  hay 

4.272 

IQ2  O 

Nitrogen-free  extract  of  starch  
Ether  extract  of  hav 

4185 
8^22 

189.8 

•377  r 

Peanut  oil       

8821 

4OO  I 

Total  organic  matter  of  roughage  

4473 

2O2.Q 

In  the  computation  of  energy  balance,  the  factors  commonly 
used  are,  for  body  protein  5.7  Cals.  per  gram  and  for  body 
fat  9.5  Cals.  per  gram,  although  Kohler's  average  for  the 
former  is  slightly  lower,  viz.,  5.628  Cals.  (88). 

The  outgo  of  chemical  energy 

Chemical  energy  supplied  in  the  feed  may  escape  unused 
for  either  of  two  reasons:  first,  the  substances  carrying  it 


230  NUTRITION  OF  FARM  ANIMALS 

may  fail  to  be  incorporated  into  the  body,  or  second,  they  may 
be  incompletely  katabolized. 

317.  The  feces.  —  Since  a  greater  or  less  proportion  of  the 
organic  matter  of  most  feeding  stuffs  fails  of  digestion  and  re- 
sorption  by  farm  animals  and  so  does  not  enter  into  the  body 
proper   (148),  a  considerable  amount  of  unused  feed  energy 
escapes  in  the  feces,  while  the  excretory  products  which  they 
carry  (154)  contain  chemical  energy  which  has  failed  of  com- 
plete conversion  in  the  body.     The  chemical  energy  of  the  feces 
of  farm  animals  constitutes  a  very  considerable  item  in  their 
total  outgo  of  energy.     Its  amount  can  be  determined  as  in 
the  case  of  feeding  stuffs  by  burning  a  sample,  after  drying 
with  suitable  precautions,  in  a  calorimeter  and  measuring  the 
heat  evolved. 

318.  Combustible  gases.  —  The  combustible  gases  produced 
by  fermentation  in  the  digestive  tract  also  carry  off  relatively 
large  amounts  of   unused   chemical   energy,  the   loss  in  this 
way   being   precisely    analogous    to    that    in    the    undigested 
matter  of  the  feces  except  that  it  escapes  in  invisible  products. 
These  gases  cannot  well  be  separated  from  the  other  gaseous 
excreta  for  the  purpose  of  making  a  direct  determination  of  their 
energy.     The  amounts  of  carbon  and  hydrogen  excreted   in 
them,  however,  can  be  determined  with  the  aid  of  the  respiration 
apparatus  and  on  the  well-founded  assumption  that  only  meth- 
ane and  hydrogen  are  produced  the  amount  of  each  excreted 
may  be  calculated.     The  heats  of  combustion  of  both  these 
gases  being  known,  the  amount  of  chemical  energy  which  they 
carry  off  can  be  readily  computed. 

319.  Products  of  incomplete  katabolism.  —  The  heat  of  com- 
bustion of  a  substance,  as  already  denned,  is  the  amount  of  heat 
evolved  when  it  is  completely  oxidized,  that  is,  in  the  case  of 
substances  prdinarily  occurring  in  feeding   stuffs,  when   it   is 
burned  to  CO2,  H2O,  N2,  and  SO3.     If  the  katabolism  in  the 
body  stops  short  of  these  end  products,  the  quantity  of  chemical 
energy  transformed  is  clearly  less  than  the  gross  energy  of  the 
substance  by  an  amount  equal  to  the  heat  of  combustion  of 
the  incompletely  oxidized  products. 

The  proteins  of  the  feed  constitute  the  most  important  in- 
stance of  this  sort.  All  the  nitrogen  of  the  digested  protein 
and  part  of  its  carbon,  hydrogen  and  oxygen,  are  excreted  in 


THE  BALANCE  OF  NUTRITION  231 

the  urine  in  the  form  of  crystalline  nitrogenous  products,  of 
which  urea  is  the  most  familiar  and  often  the  most  abundant. 
When  these  products  are  burned  they  yield  a  certain  amount 
of  heat,  thus  showing  that  they  still  contain  part  of  the  gross 
energy  of  the  protein,  and  that,  therefore,  only  a  portion  of  the 
latter  has  been  transformed  in  the  body. 

320.  The  urine.  —  In  the  main,  the  urine  is  the  vehicle  for  the 
removal  from  the  body  of  the  incompletely  oxidized  products 
of  katabolism,  although  some  unoxidized  or  partially  oxidized 
material  also  escapes  from  the  body  in  the  form  of  the  excretory 
products  contained  in  the  feces  (317),  and  small  amounts  of 
chemical   energy   are   contained   in   the   cutaneous   excretory 
products  (198). 

The  energy  of  the  katabolic  products  contained  in  the  urine 
may  be  determined  as  in  the  case  of  the  feces  by  burning  the 
dried  residue  in  the  calorimeter,  a  small  correction  being  usually 
necessary  for  unavoidable  losses  in  drying. 

An  approximate  calculation  of  the  chemical  energy  of  the  urine 
may  be  based  upon  its  nitrogen  or  better  on  its  carbon  content,  using 
the  average  ratio  found  in  experiments  on  the  same  species,  but  these 
ratios  vary  more  or  less  in  different  cases,  and  in  exact  work  direct 
determinations  are  called  for. 

321.  Cutaneous  excretion.  —  The  amount  of  chemical  energy 
removed  in  the  perspiration  is  too  small  to  be  of  any  significance, 
except  possibly  in  experiments  on  severe  work. 

In  addition  to  the  perspiration  there  is  a  continual  small  loss 
of  matter  with  its  accompanying  chemical  energy  in  the  form 
of  epidermal  scales,  hair,  etc.,  sloughed  off.  These  losses  are 
comparable  to  the  excretory  products  in  the  feces,  since  they 
consist  essentially  of  incompletely  katabolized  body  material. 
Their  amount  is  small  but  is  sufficient  to  be  taken  account  of 
in  exact  experiments. 

Metabolizable  energy 

322.  General  conception.  —  It  has  been  shown  in  the  fore- 
going paragraphs  that  more  or  less  of  the  chemical  energy  of 
the  feed  escapes  unused  from  the  body,  the  total  thus  rejected 
being  equal  to  the  gross  energy  of  the  total  excreta,  solid,  liquid 


232  NUTRITION  OF  FARM  ANIMALS 

and  gaseous,  as  measured  by  their  heats  of  combustion.  If, 
then,  the  gross  energy  of  the  total  excreta  be  subtracted  from 
the  gross  energy  of  the  feed,  the  remainder  shows  how  much 
of  the  chemical  energy  of  the  feed  can  be  metabolized,  that  is, 
converted  into  other  forms  in  the  organism.  To  this  difference, 
the  term  metabolizable  energy  has  been  applied. 

Metabolizable  energy  may  be  briefly  defined  as  the  gross 
energy  of  the  feed  minus  the  gross  energy  of  the  excreta.  Thus 
in  the  experiment  cited  previously  (294)  to  illustrate  the 
method  of  determining  the  balance  of  matter,  the  energy  content 
of  the  feed  and  excreta  and  the  metabolizable  energy  of  the 
total  ration  were  as  follows :  — 

Energy  of  feed 

6988  grms.  timothy  hay 27,727  Cals. 

400  grms.  linseed  meal 1811  Cals. 

29,538  Cals. 
Energy  of  excreta 

16,619  grms.  feces 14,243  Cals. 

4357  grms.  urine 1210  Cals. 

142  grms.  methane       ....        1896  Cals. 

Total !     !     !     .     17,349  Cals. 

Metabolizable  energy 12,189  Cals. 

It  should  be  observed  that  the  foregoing  definition  makes  no 
assertion  whatever  as  to  the  forms  into  which  the  metabolizable 
energy  has  been  transformed  nor  as  to  the  degree  to  which  the 
transformation  has  been  of  service  to  the  organism.  Some  of 
the  energy,  for  example,  may  be  retained  in  the  body  in  a  gain 
of  fat  or  protein,  as  in  the  illustration  just  given,  i.e.,  it  may 
be  temporarily  set  aside  as  a  reserve  to  be  used  later,  but  it  is 
still  capable  of  transformation  into  other  forms  and  therefore 
constitutes  a  part  of  the  metabolizable  energy.  On  the  other 
hand,  the  feed  might  contain  some  substance  capable  of  oxida- 
tion in  the  body  but  of  no  physiological  value  to  it  and  which 
was  simply  burned  to  get  rid  of  it.  The  heat  thus  generated 
might  be  entirely  useless  to  the  animal,  yet  this  energy 
would  be  part  of  the  metabolizable  energy  of  the  feed.  Some- 
what similarly,  the  energy  liberated  as  heat  in  the  methane 
fermentation  constitutes  part  of  the  metabolizable  energy, 
although  it  does  not  enter  into  the  tissue  metabolism.  Metab- 


THE   BALANCE   OF  NUTRITION  233 

olizable  energy  means  simply  energy  capable  of  transformation 
in  the  body.  It  is  the  maximum  quantity  which  the  feed  can 
contribute  to  the  energy  changes  in  the  organism.  That  it 
does  not  necessarily  measure  nutritive  value  is  indeed  suffi- 
ciently apparent  from  the  method  used  for  its  determination. 
As  the  example  already  given  shows,  this  does  not  require  any 
measurement  of  the  gain  or  loss  by  the  animal,  but,  like  a 
digestion  experiment,  concerns  itself  simply  with  the  feed  and 
the  excreta. 

323.  Synonyms  for  metabolizable  energy.  —  Two  other 
terms  are  frequently  employed  with  substantially  the  same 
significance  as  metabolizable  energy,  viz.,  fuel  value  and  avail- 
able energy. 

Fuel  value.  —  The  metabolizable  energy  of  the  feed  is  evi- 
dently capable  of  conversion  into  heat  in  the  body.  Since  a 
considerable  portion  and  sometimes  all  of  it  is  actually  thus 
converted,  and  since  its  amount  is  usually  expressed  as  a  matter 
of  convenience  in  heat  units,  the  term  fuel  value  (or  physiological 
heat  value)  has  come  into  use  as  synonymous  with  metaboliz- 
able energy. 

The  term  has  the  advantage  of  brevity,  but  has  also  certain 
disadvantages.  In  conjunction  with  the  unit  of  measurement 
employed,  it  has  a  tendency  to  suggest  that  the  purpose  of 
the  feed  is  to  supply  heat  energy  and  that  it  is  of  value 
in  proportion  as  it  can  do  this,  which  is  far  from  being  the 
case.  Moreover,  there  appears  to  be  some  danger  of  confusion 
due  to  the  fact  that  the  same  term  is  used  in  a  different  sense 
in  relation  to  fuels.  The  "  fuel  value  "  of  a  coal,  for  example, 
means  the  total  amount  of  heat  which  it  liberates  when  burned, 
and  corresponds,  therefore,  to  the  gross  energy  of  a  feeding  stuff, 
i.e.,  to  its  value  if  used  as  fuel  under  a  boiler  or  in  a  heating 
plant.  The  fuel  value  of  a  feeding  stuff,  on  the  other  hand,  in 
the  sense  of  its  metabolizable  energy,  is  the  amount  of  heat 
which  it  can  furnish  when  oxidized  as  it  is  in  the  body,  i.e.,  more 
or  less  incompletely. 

Available  energy.  —  A  much  more  unfortunate  usage  is  the 
employment  of  the  term  available  energy,  equivalent  to  the 
German  "  Physiologischer  Nutzwert,"  in  the  sense  here  assigned 
to  metabolizable  energy.  This  usage  dates  back  to  Rubner's 
investigations  of  the  replacement  values  of  nutrients  in  1882- 


234 


NUTRITION  OF   FARM   ANIMALS 


1885  and  to  his  isodynamic  values  based  upon  them.  In  the 
light  of  the  knowledge  available  at  that  time,  this  use  of  the 
term  was  perhaps  justified,  but  as  will  appear  later  (369),  it  has 
since  been  shown  that  part  of  the  metabolizable  energy  of  the 
feed  is  virtually  available  for  heat  production  alone,  while  only 
the  remainder  can  be  used  for  general  body  purposes.  If  the 
use  of  the  term  available  energy  is  to  be  continued,  therefore, 
it  becomes  necessary  to  distinguish  two  degrees  of  avail- 
ability, using,  for  instance,  the  term  gross  available  energy  as 
equivalent  to  metabolizable  energy  and  net  available  energy 
•to  signify  that  part  of  the  metabolizable  energy  which  is  avail- 
able for  other  purposes  than  heat  production. 

In  the  writer's  judgment,  simplicity  and  clearness  of  concep- 
tion will  be  promoted  by  discontinuing  altogether  the  use  of  the 
term  available  energy  and  employing  the  term  metabolizable 
energy,  or  perhaps  fuel  value  provided  the  latter  is  understood 
with  the  proper  restrictions,  to  designate  that  portion  of  the 
gross  energy  of  the  feed  which  is  capable  of  transformation  in 
the  animal  organism. 

324.  Factors  for  metabolizable  energy.  —  Rubner,  and 
subsequently  Atwater,  have  proposed  factors  by  the  use  of 
which  the  metabolizable  energy  of  the  diet  of  man  may  be 
computed  with  a  considerable  degree  of  accuracy.1 

TABLE  27.  —  FACTORS  FOR  METABOLIZABLE  ENERGY  OF  HUMAN  FOOD 


RUBNER 
Per  gram  digested 
nutrients 

ATWATER 
Per  gram  total 
nutrients 

Protein 

Cals. 

A    I 

Cals. 

A    O 

Carbohydrates                                .... 

4.1 

4.O 

Fats     

9-3 

8.Q 

The  use  of  these  same  factors  yields  approximately  correct 
results  for  carnivora.  They  have  sometimes  been  applied  also 
to  the  digestible  nutrients  of  the  feed  of  herbivora  but  without 
sufficient  warrant. 


Compare  the  writer's  Principles  of  Animal  Nutrition,  pp.  272-281. 


THE   BALANCE  OF   NUTRITION  235 


The  outgo  of  work  and  heat  from  the  body 

325.  Outgo  of  kinetic  energy.  —  The  feces,  urine,  combus- 
tible gases  and   cutaneous   excreta  carry   off   chiefly  unused 
chemical  energy.1    To  recur  to  the  illustration  of  the  internal 
combustion  motor,   they  are  comparable  with  losses  due  to 
leakage  or  incomplete  combustion  of  the  fuel.     The  energy  re- 
maining after  these  losses  have  been  met,  i.e.,  the  metabolizable 
energy,  may  be  converted  in  part  into  mechanical  work  and 
in  part  into  heat. 

When  an  animal  performs  work,  whether  in  drawing  a  load, 
carrying  a  rider,  operating  a  tread  power  or  simply  lifting 
the  weight  of  his  own  body  at  each  successive  step,  a  portion, 
although  on  the  whole  a  relatively  small  percentage,  of  his  total 
income  of  chemical  energy  is  expended  in  moving  objects,  i.e.,  is 
converted  into  kinetic  energy.  The  kinetic  energy  thus  pro- 
duced may  be  measured  in  accordance  with  the  general  methods 
described  in  a  previous  paragraph  (313),  usually  by  conversion 
into  gravitation  energy  and  measurement  in  gravitation  units, 
i.e.,  the  gram  meter,  kilogram  meter  or  foot  pound. 

326.  Outgo  of  heat.  —  The  outgo  of  heat  which  common 
experience  teaches  is  continually  taking  place  from  the  bodies 
of  men  and  of  animals  represents  a  very  considerable  share  of 
the  total  income  of  chemical  energy.     It  has  been  computed 
that  if  the  heat  produced  by  the  average  healthy  man  could 
be  prevented  from  escaping  from  the  body  it  would  in  a  single 
day  raise  it  to  a  pasteurizing  temperature,  while  in  the  course 
of  a  month  at  the  same  rate,  the  temperature  would  be  raised 
approximately  to  that  of  melting  cast  iron. 

327.  Animal  calorimeters.  —  The  great  variety  of  animal 
calorimeters  which  have  been  devised  for  the  purpose  of  measur- 
ing the  heat  production  of  living  animals  have  been  of  three 
general  types,  which  may  be  designated  as  water  calorimeters, 
latent  heat  calorimeters  and  emission  calorimeters. 

Water  calorimeters  are  those  in  which  the  heat  is  imparted 
to  a  known  quantity  of  water,  the  rise  of  temperature  of  which 
is  measured,  i.e.,  they  employ  the  first  of  the  two  methods  of 

1  The  heat  which  they  also  carry  off  is  included  in  the  total  outgo  of  heat  con- 
sidered in  the  next  paragraph. 


236  NUTRITION  OF  FARM  ANIMALS 

measuring  heat  previously  described  (309).  Water  calorim- 
eters may  be  subdivided  into  those  in  which  the  heat  is  im- 
parted to  a  stationary  mass  of  water  and  those  called  flow 
calorimeters,  in  which  it  is  taken  up  by  a  current  of  water. 

Latent  heat  calorimeters  make  use  of  the  second  method  of 
heat  measurement,  viz.,  causing  it  to  effect  a  change  in  the 
physical  state  of  the  calorimetric  substance.  Thus  Lavoisier 
employed  an  ice  calorimeter  in  his  experiments  upon  the  re- 
lations between  respiration  and  heat  production.  This  type  of 
calorimeter,  however,  is  not  well  suited  to  experiments  with 
animals  and  has  been  but  little  used. 

Emission  calorimeters  may  be  said  not  to  be  in  a  strict  sense 
calorimeters  at  all,  i.e.,  they  do  not  serve  directly  to  measure 
quantities  of  heat  but  only  to  compare  the  rate  of  heat  pro- 
duction by  different  sources,  but  they  may  be  used  indirectly 
to  measure  quantities.  The  principle  of  the  emission  calorim- 
eter may  be  illustrated  as  follows :  If  a  known  source  of  heat 
(an  electric  resistance,  for  example)  be  placed  in  a  closed  recepta- 
cle located  in  a  room  kept  at  constant  temperature,  it  will  tend 
to  heat  the  walls  of  the  container.  As  the  temperature  of  the 
walls  rises,  however,  heat  will  be  radiated  from  them  with  in- 
creasing rapidity  until  a  balance  is  established  between  heat 
radiation  and  heat  production  and  the  temperature  of  the 
walls  remains  constant.  If,  now,  a  second  source  of  heat, 
an  animal,  for  example,  be  substituted  for  the  first  one, 
keeping  the  external  conditions  the  same,  and  if  it  appears  that, 
when  an  equilibrium  is  reached,  the  temperature  of  the  walls  is 
the  same  as  in  the  first  case,  it  is  concluded  that  the  rate  of 
heat  radiation  is  the  same  as  in  the  first  case,  and  that  the 
animal  is  producing  heat  at  the  same  rate  as  was  the  electric 
resistance,  so  that  the  amount  of  heat  produced  by  the  animal 
in  a  unit  of  time  is  thus  indirectly  measured. 

The  respiration  calorimeter.  —  All  animal  calorimeters  used 
for  experiments  of  any  length  must  necessarily  be  provided 
with  ventilation.  To  prevent  a  loss  of  heat  in  the  air  current, 
it  is  introduced  at  the  same  temperature  as  that  at  which  it 
leaves  the  apparatus.  The  ventilating  air  current,  however, 
tends  to  remove  water  vapor  from  the  chamber  and  the  evapo- 
ration of  this  water,  of  course,  absorbs  a  corresponding  amount 
of  heat  as  the  so-called  "  latent  heat  of  evaporation  "  of  water. 


THE    BALANCE    OF    NUTRITION 


237 


Either,  therefore,  evaporation  must  be  prevented  by  keeping 
the  air  in  the  chamber  saturated  with  water,  thus  introducing 
more  or  less  abnormal  conditions,  or  the  amount  of  water 
carried  away  in  the  ventilating  air  current  must  be  determined. 
If  the  latter  course  is  followed,  it  is  a  relatively  simple  matter 
to  include  also  determinations  of  the  carbon  dioxid  and  the 
combustible  gases  excreted,  and  perhaps  of  the  oxygen  con- 


FIG.  34.  —  Dulong's  water  calorimeter  (Schaefer,  Text  Book  of  Physiology). 


sumed.  The  apparatus  then  becomes  a  combination  of  res- 
piration apparatus  and  animal  calorimeter  and  hence  has  been 
called  a  respiration  calorimeter. 

The  apparatus  used  by  Dulong  in  1822  in  his  investigation  of  the 
source  of  animal  heat,  the  construction  of  which  is'shown  in  Fig.  34, 
may  serve  to  illustrate  the  form  of  calorimeter  in  which  a  stationary 
mass  of  water  is  used.  This  type  of  calorimeter  has  been  used  in 
various  modifications,  notably  in  the  United  States  by  Wood,1  Ott  2 

1  Smithsonian  Contributions  to  Knowledge,  No.  23  (1880). 
2N.  Y.  Med.  Jour.,  49  (1889),  342. 


238 


NUTRITION  OF  FARM  ANIMALS 


THE   BALANCE  OF  NUTRITION  239 

and  Reichert.1  It  is,  however,  not  readily  adapted  for  use  with  large 
animals,  both  on  account  of  the  difficulty  in  determining  the  true 
average  temperature  of  a  large  mass  of  water  and  on  account  of  the 
great  weight  of  such  an  instrument. 

The  best  known  and  most  successful  form  of  flow  calorimeter  for 
experiments  upon  animals  is  that  devised  by  Atwater  and  Rosa 2  and 


I 


FIG.  36. 

modified  by  Atwater  and  Benedict3  for  experiments  on  man  and 
adapted  by  Armsby  and  Fries 4  and  by  Hagemann  5  for  experiments  on 
the  larger  farm  animals.  Figure  35  shows  the  general  appearance  of 
the  apparatus  constructed  by  Armsby  and  Fries. 

The  most  familiar  form  of  emission  calorimeter  is  that  of  Rubner,6 
in  which  the  changes  in  volume  of  the  air  enclosed  between  the  double 
walls  of  the  animal  chamber  constitutes  the  indicator.  Figure  36 
shows  the  general  appearance  of  the  Rubner  apparatus.  A  very 
similar  one  has  been  devised  by  Rosenthal7  in  which  the  pressure  of 
the  confined  air  at  constant  volume  serves  as  the  indicator. 

1  University  Med.  Mag.,  1890,  ii,  173. 

2  U.  S.  Dept.  Agr.,  Office  Expt.  Stas.,  Bui.  63  (1899) ;  Bui.  136  (1903). 
8  Carnegie  Institution  of  Washington,  Publication  No.  42  (1905). 

4U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  51,  (1903);  and  Experiment  Station 
Record,  15  (1903-1904),  1037. 

5Landw.  Jahrb.,  41  (1911),  Erganzbd.  I. 

6Ztschr.  Biol.,  30  (1894),  91-  7  Arch.  (Anat.  u.)  Physiol.,  1894,  P-  223. 


240 


NUTRITION  OF  FARM  ANIMALS 


An  interesting  form  of  emission  calorimeter  is  the  so-called  com- 
pensation calorimeter,  in  which  the  heat  produced  by  the  subject  is 
balanced  against  that  produced,  for  example,  by  burning  pure  hydro- 
gen or  by  an  electrical  resistance  in  a  precisely  similar  chamber. 
Calorimeters  of  this  type  have  been  described  by  Haldane, 1  Bohr  2 
and  recently  by  Tangl.3 

328.  Summary.  —  The  foregoing  facts  may  be  summarized 
in  the  following  tabular  statement  showing  the  several  items  of 
income  and  outgo  of  energy  as  well  as  the  particular  form  of 
energy  contained  in  each. 


Income: 


Outgo : 


Feed 

Feces 

Urine 

Perspiration 

Combustible  gases 

Work 

Heat 


Chemical  energy 


Kinetic  energy 
Heat  energy 


329.  Example  of  an  energy  balance.  —  The  same  experiment 
upon  a  steer  for  which  the  nitrogen  and  carbon  balance  and 
the  metabolizable  energy  (290,  294,  322)  have  already  been 
computed  may  also  serve  to  illustrate  the  determination  of  the 
energy  balance.  In  this  experiment  the  animal  performed  no 
external  work,  so  that  no  energy  had  to  be  measured  in  that 
form. 

TABLE  28.  —  DAILY  ENERGY  BALANCE  OF  A  STEER 


INCOME 

OUTGO 

6988  grms  timothy  hay    

Cals. 

27,727 

Cals. 

400  grms.  linseed  meal    
16,610  grms  feces            ...          . 

1811 

14,243 

4357  grms.  urine  

I2IO 

37  grms  brushings 

00 

142  grms.  methane      

1866 

Heat 

II  4.Q3 

Gain  by  body     .                   .... 

608 

29,S38 

29,538 

1  Jour.  Physiol.  (London),  16  (1894),  123. 

2  Skand.  Arch.  Physiol.,  14  (1903),  398. 


8  Biochem.  Ztschr.,  53  (1913),  21. 


THE  BALANCE  OF  NUTRITION  241 

According  to  the  conception  of  the  schematic  body  (280), 
these  figures  show  that  energy  to  the  extent  of  608  Cals.  was 
stored  up  in  the  body  as  the  chemical  energy  of  either  protein, 
fat  or  glycogen.  Assuming  that  there  was  no  change  in  the 
glycogen  content  of  the  animal,  the  nitrogen  and  carbon  balance 
showed  a  computed  storage  of  66.6  grams  of  protein  and  15.2 
grams  of  fat  (294).  The  average  chemical  energy  of  protein  is 
5.7  Cals.  per  gram  and  that  of  fat  9.5  Cals.  per  gram.  The 
amounts  of  energy  stored  up  in  the  fat  and  protein  gained  by  the 
steer  can  therefore  be  computed  as  follows : 

In  protein  5.7  Cals.  X  66.6  =  380  Cals. 
In  fat         9.5  Cals.  X  15.2  =  144  Cals. 
Total  524  Cals. 

Found  from  energy  balance       608  Cals. 
Difference  84  Cals. 

It  thus  appears  that  in  this  experiment  the  gain  of  energy 
found  by  a  direct  determination  of  the  energy  balance  and  that 
computed  from  the  balance  of  nitrogen  and  carbon  agreed 
within  84  Cals.,  or  0.3  per  cent  of  the  total  amount  of  energy 
involved.  It  is  evident  that  determinations  of  the  nitrogen 
and  carbon  balance  on  the  one  hand  and  of  the  energy  balance 
on  the  other  may  serve  as  a  mutual  check,  and  also  that  the 
heat  production  of  an  animal  may  be  computed  quite  accurately 
from  determinations  of  the  nitrogen  and  carbon  balances  (in- 
direct calorimetry.) 


§  5.  SIGNIFICANCE  OF  RESULTS 

Studies  of  the  balance  of  nutrition  have  played  a  very  promi- 
nent role  in  both  physiological  and  agricultural  investigation. 
Having  considered  in  the  foregoing  pages  the  general  methods 
of  the  balance  experiment,  a  brief  consideration  of  the  signifi- 
cance of  the  results  obtained  by  their  use  as  compared  with  those 
reached  by  other  methods  seems  called  for. 

330.  Comparison  with  metabolism  investigations.  —  The 
results  of  experiments  like  the  one  with  a  steer  used  as  an 
illustration  in  previous  paragraphs  show,  within  the  limits  of 
experimental  error,  the  loss  or  the  storage  of  chemical  energy 


242  NUTRITION  OF   FARM   ANIMALS 

resulting  from  the  use  of  a  certain  feed  or  ration  and  approxi- 
mately in  what  kind  of  material  (protein,  fat,  gJycogen)  the 
energy  lost  or  gained  was  contained/  The  balance  experiment, 
therefore,  is  adapted  to  determine  the  total  nutritive  effect  of 
a  given  substance,  while  if  the  comparative  slaughter  test  be 
regarded  as  a  form  of  balance  experiment  (284)  the  particular 
organs  or  tissues  in  which  gain  or  loss  took  place  can  be  deter- 
mined. 

The  balance  experiment,  however,  affords  no  insight  into  the 
details  of  the  chemical  mechanism  by  which  the  observed  nu- 
tritive result  is  brought  about.  For  example,  balance  experi- 
ments have  demonstrated  that  starch  may  serve  as  a  source  of 
fat  and  have  shown  quantitatively  the  amount  of  fat  formed 
from  a  given  weight  of  starch.  As  applied  to  known  chemical 
compounds,  such  a  result  as  this  is  perfectly  definite  and  of  the 
highest  value,  but  it  gives  absolutely  no  information  as  to  the 
intermediate  steps  of  fat  formation,  either  in  the  processes  of 
digestion,  resorption  or  metabolism. 

On  the  other  hand,  investigations  of  the  intermediary  metab- 
olism, like  those  whose  main  results  have  been  outlined  in 
Chapter  V,  have  necessarily  been  to  a  large  extent  qualitative. 
They  have  demonstrated  some  of  the  steps  through  which  the 
various  anabolisms  and  katabolisms  occur,  but  as  a  rule  have 
not  attempted  to  deal  directly  with  quantitative  questions.1 

Naturally  the  foregoing  comparison  is  neither  comprehensive  nor 
exclusive.  It  aims  simply  to  point  out  a  broad  general  distinction 
between  two  types  of  nutrition  investigation  which  in  reality  shade 
into  each  other. 

Balance  experiments  have  sometimes  been  characterized, 
with  a  certain  half  contemptuous  implication,  as  "  bookkeeping 
with  the  body."  The  characterization  is  a  good  one  but  the 
implication  is  unwarranted.  It  is  perfectly  true,  as  some  critics 
of  the  balance  experiment  point  out,  that,  for  example,  the  most 
accurate  record  of  the  income  of  raw  materials  and  outgo  of 
finished  products  would  of  itself  give  a  very  incomplete  notion 
of  the  operations  of  a  great  factory  and  that  the  successful 
conduct  of  such  an  enterprise  requires  as  intimate  a  knowl- 

1  For  a  summary  of  some  of  the  more  important  of  these  methods  compare 
Dakin,  Oxidations  and  Reductions  in  the  Animal  Body,  Chapter  III. 


THE    BALANCE    OF    NUTRITION  243 

edge  as  possible  of  the  functions  of  each  separate  machine 
and  of  the  changes  undergone  by  the  materials  submitted  to 
its  action. 

It  may  fairly  be  presumed,  however,  that  these  critics,  even 
with  the  fullest  knowledge  of  the  technical  details  of  such  a 
factory,  would  hardly  undertake  to  conduct  it  as  a  business 
enterprise  without  keeping  account  of  the  stock  purchased  and 
the  output  realized,  i.e.,  exactly  the  sort  of  bookkeeping  which 
the  balance  experiment  attempts  for  the  animal  body.  The 
truth  is  that  both  types  of  investigation  are  equally  necessary 
and  each  aids  in  the  interpretation  of  the  other.  The  balance 
experiment  has  been  especially  prominent  in  the  past,  while  at 
present  attention  is  being  directed  to  a  greater  extent  to  in- 
vestigations of  the  intermediary  metabolism,  but  neither  can 
say  to  the  other  "  I  have  no  need  of  thee." 

331.  The  balance  experiment  in  agricultural  investigations. 
—  As  already  indicated,  the  methods  of  the  balance  experiment 
have  been  quite  largely  applied  in  agricultural  investigations. 
Such  investigations  have  been  made,  in  the  majority  of  cases, 
not  with  single  chemical  compounds,  but  with  feeding  stuffs 
or  rations  as  a  whole,  and  the  effect  observed  in  such  an  ex- 
periment is  obviously  a  summation  of  the  effects  of  all  the 
ingredients  contained  in  the  feed  consumed.  The  result,  there- 
fore, while  entirely  adequate  to  determine  the  total  nutritive 
effect  of  the  particular  material  experimented  with  is  less  capable 
of  generalization  than  one  obtained  with  a  single  chemical 
compound  like  starch  or  fat,  and  from  this  point  of  view  may 
even  be  regarded  as  being  in  a  sense  empirical.  A  compre- 
hensive knowledge  of  the  nutritive  value  of  a  feeding  stuff  im- 
plies, first,  a  determination  of  the  kinds  and  amounts  of  chemical 
compounds  contained  in  it  and,  second,  a  determination  of  the 
exact  physiological  functions  of  each.  Obviously,  however, 
such  a  complete  determination  of  the  nutritive  value  of  any 
considerable  number  of  feeding  stuffs  is  a  work  requiring  a  vast 
expenditure  of  time  and  labor.  One  justification,  therefore,  for 
the  "  short-cut  "  method  of  determining  summarily  by  a. bal- 
ance experiment  the  effect  of  a  feeding  stuff  or  ration  is  that  it 
appears  possible  to  secure  in  this  way  within  a  reasonable  time 
data  which  can  be  put  to  practical  use  in  the  comparison  of 
feeding  stuffs  and  rations.  Moreover,  it  is  to  be  anticipated 


244  NUTRITION   OF   FARM   ANIMALS 

that  the  conclusions  as  to  the  nutritive  value  of  any  material 
drawn  from  even  the  most  elaborate  chemical  and  physio- 
logical investigations  will  need  finally  to  be  checked  and  con- 
firmed by  the  methods  of  the  balance  experiment. 

The  value  of  the  balance  experiment  in  relation  to  stock 
feeding,  however,  is  far  from  being  limited  to  the  summary 
determination  of  the  total  nutritive  values  of  feeding  stuffs, 
although  it  has  rendered  important  service  in  that  field. 

As  will  become  apparent  in  Part  III,  the  feed  requirements 
for  animals  for  various  purposes,  as  well  as  the  general  physio- 
logical laws  governing  the  processes  of  maintenance,  growth, 
fattening,  milk  production,  the  performance  of  work,  etc.,  can 
be  successfully  studied  only  with  the  aid  of  balance  experi- 
ments, and  the  results  obtained  in  such  experiments  are  of 
general  scientific  value  independent  of  the  particular  feeding 
stuff  used.  A  striking  illustration  of  the  importance  of  such 
investigations  on  farm  animals  is  afforded  by  the  results  ob- 
tained by  Zuntz  and  his  associates,  by  Kellner  and  others  re- 
garding the  expenditure  of  energy  in  the  digestion  and  assimi- 
lation of  the  feed  (365-370).  The  marked  differences  between 
these  animals  and  man  or  carnivora  as  regards  the  character 
of  the  feed  and  of  the  digestive  processes  have  served  to  make 
prominent  certain  factors  of  the  so-called  "  work  of  digestion  " 
which  were  inconspicuous  in  the  latter  subjects  and  thus  the 
investigations  have  yielded  important  contributions  to  com- 
parative physiology. 

332.  Comparison  with  practical  experiments.  —  Finally,  it 
should  be  observed  that  the  methods  of  exact  feeding  experi- 
ments based  on  a  determination  of  the  balance  of  matter  and 
energy  do  not  differ  in  their  ultimate  logical  basis  from  those  of 
so-called  "  practical  "  experiments.  In  both  cases,  the  meas- 
ure of  the  nutritive  value  of  a  feeding  stuff,  of  the  influence  of 
changed  conditions,  or  of  the  efficiency  of  the  animal  as  a  food 
producer,  is  the  effect  upon  the  animal.  The  difference  lies 
in  the  accuracy  and  degree  of  detail  with  which  that  effect  is 
determined.  The  reasons  for  the  inadequacy  of  the  live  weight 
as  a  measure  of  nutritive  effect  have  already  been  considered 
(281-283),  while  the  experience  of  more  than  50  years  has 
sufficiently  demonstrated  that  the  attempt  to  measure  nutritive 
effects  by  changes  in  the  weight  of  the  animal  or  by  the  gross 


THE   BALANCE   OF  NUTRITION  245 

product  yielded  fails  to  give  results  which  are  consistent  with 
each  other  or  which  permit  of  the  formulation  of  general  prin- 
ciples. Only  the  laborious  methods  of  the  balance  experiment 
or  the  refinements  of  physiological  investigation  can  be  relied 
upon  to  reveal  those  fundamental  laws  upon  which  the  suc- 
cessful practice  of  stock  feeding  depends. 


PART  III 
THE    FEED    REQUIREMENTS 


CHAPTER  VII 
THE   FASTING  KATABOLISM 

333.  Significance.  —  It  is  a  familiar  fact  that  in  the  absence 
of  feed  the  life  of  the  animal  can  be  supported  for  a  time  at  the 
expense  of  the  materials  of  the  body  itself.     If  sufficient  water 
and  oxygen  be  supplied,  those  metabolic  processes  by  which 
energy  is  liberated  for  the  physiological  activities  of  the  body 
(201,  207)  may  continue  for  a  considerable  period,  although,  of 
course,  they  are  ultimately  halted  by  lack  of  material  or  im- 
pairment  of   the   integrity   of    the   protoplasm.     The   fasting 
animal  in  a  state  of  rest,  therefore,  affords  an  opportunity  to 
study  the  demands  of   the  fundamental  vital  processes  un- 
complicated by  the  functions  of  digestion  and  resorption  or  by 
the  requirements  of  growth,  fattening  or  reproduction. 

A  qualitative  and  quantitative  knowledge  of  the  expenditure 
of  matter  and  of  energy  by  the  fasting  animal,  then,  is  obviously 
an  important  step  towards  ascertaining  the  supply  of  feed 
necessary  for  various  purposes. 

334.  Substances   katabolized.  —  All    the   principal    compo- 
nents of  the  body  may  be  katabolized  and  yield  energy  for  the 
support  of  the  fasting  organism. 

Fat.  —  It  is  a  familiar  conception  that  fat  formation  is  the 
body's  method  of  disposing  of  surplus  feed,  and  that  the  body 
fat  is  a  store  of  reserve  fuel  material.  The  converse  of  this 
fact  is  equally  familiar.  The  fasting  or  insufficiently  fed  ani- 
mal loses  fat,  and  may  reach  a  stage  of  extreme  emaciation  be- 
fore the  active  tissues  fail  to  perform  their  functions.  Obviously, 
the  fasting  animal  lives  largely  upon  its  reserve  of  fat.  These 
conclusions  from  common  observation  have  been  fully  con- 
firmed by  comparative  analysis  of  the  carcasses  of  well-fed  and 
of  fasted  animals  as  well  as  by  the  results  of  balance  experiments 
in  which  the  exact  nature  of  the  outgo  from  the  body  has  been 
determined. 

Carbohydrates.  —  In  addition  to  fat  the  body  contains  more 
or  less  non-nitrogenous  matter  in  the  form  of  glycogen  in  the 

249 


25° 


NUTRITION  OF   FARM   ANIMALS 


liver  and  muscles.  During  the  first  few  days  of  fasting,  this 
store  of  carbohydrates  is  also  drawn  upon,  as  is  indicated  by 
the  fact  that  the  respiratory  quotient  tends  to  approach  unity, 
while  later  the  amount  of  glycogen  katabolized  becomes  very 
small. 

Protein.  —  Balance  experiments,  however,  while  confirming 
the  conclusion  that  the  loss  of  tissue  in  fasting  usually  consists 
chiefly  of  fat  together  with  some  carbohydrates,  show  that  there 
is  also  a  continual  katabolism  of  body  protein  and  a  corre- 
sponding excretion  of  urinary  nitrogen.  While  the  energy 
expended  by  the  fasting  animal  is  derived  chiefly  from  the 
breaking  down  of  non-nitrogenous  material,  the  functional 
activities  of  the  body  necessarily  involve  the  katabolism  of  a 
certain  minimum  amount  of  protein. 

Ash.  —  Finally,  in  addition  to  those  groups  of  substances 
whose  katabolism  yields  energy  to  the  body,  the  so-called  min- 
eral elements,  or  ash,  of  the  body  take  part  in  the  processes  of 
katabolism  and  are  continuously  excreted  in  the  urine  of  the 
fasting  animal. 

The  foregoing  facts  are  well  illustrated  by  Benedict's  l  inves- 
tigations upon  inanition.  The  average  results  of  a  number  of 
experiments  in  which  men  fasted  for  from  two  to  seven  con- 
secutive days  were  as  follows :  - 

TABLE  29.  —  AVERAGE  KATABOLISM  OF  FASTING  MEN 


ft 

O  UD 

TOTAL  KATABOLISM 

KATABOLISM  PER  KILO- 
GRAM BODY  WEIGHT 

SB 

hiC/3 

Protein 

Fat 

Glycogen 

Protein 

Fat 

Glyco- 

£ 

Grms. 

Grms. 

Grms. 

Grms. 

Grms. 

Grms. 

First  day     .... 

14 

6o.2 

I35-I 

IIO.O 

0.94 

2.10 

1.69 

Second  day      .     .     . 

14 

76.6 

165.9 

40.3* 

.21 

2.61 

0.62* 

Third  day   .     .     .     . 

6 

78.5 

155-2 

21.8 

.28 

2-54 

0.36 

Fourth  day      .     .     . 

5 

68.6 

147.2 

23-3 

•15 

2.47 

0.40 

Fifth  day    .... 

2 

62.6 

146.4 

8.2* 

.11 

2.61 

0.14* 

Sixth  day    .... 

I 

64.4 

129.8 

21.7 

.14 

2.30 

0.38 

Seventh  day     .     .     . 

I 

60.8 

132.5 

18.7 

.08 

2.36 

o-33 

1  The  Influence  of  Inanition  on  Metabolism ;  Carnegie  Institution  of  Washington, 
Publication  No.  77  (1907),  pp.  456-464. 

*  Omitting  one  case  in  which  a  small  gain  of  glycogen  was  observed. 


THE  FASTING  KATABOLISM 


251 


§  i.   THE  PROTEIN  KATABOLISM  IN  FASTING 

335.  Protein  katabolism  normally  small.  —  In  view  of  the 
structural  functions  of  the  proteins  (264),  it  is  of  some  im- 
portance to  inquire  what  proportion  of  the  total  energy  require- 
ment is  supplied  by  these  substances. 

This  aspect  of  the  subject  has  been  considered  especially  by 
E.  Voit,1  who  has  compiled  and  discussed  the  results  of  a  con- 
siderable number  of  experiments  upon  fasting.  While  some  of 
his  computations  are  based  on  estimates,  they  are  sufficiently 
accurate  to  outline  definitely  the  main  features  of  the  fasting 
katabolism.  They  show  that  in  what  may  be  spoken  of  as  the 
normal  fasting  animal,  in  which  the  influence  of  the  previous 
feeding  has  disappeared  and  in  which,  on  the  other  hand,  the 
fat  reserve  has  not  been  exhausted,  the  protein  katabolism  sup- 
plies a  rather  small  proportion  of  the  total  energy  transformed, 
the  percentage  with  dogs,  e.g.,  ranging  in  the  majority  of  cases 
between  10  and  17. 

336.  Fasting  protein  katabolism  variable.  —  It  is  not  true, 
however,  as  has  sometimes  been  loosely  stated  on  the  basis  of 
C.  Voit's  experiments  (338),  that  the  protein  katabolism  of  a 
fasting  animal  becomes  constant  within  a  short  time.     On  the 
contrary,  in  the  presence  of  an  adequate  amount  of  body  fat, 
its  amount  tends  to  diminish  with  the  progress  of  fasting.     For 
example,  in  one  of  Benedict's  fasting  experiments  (Table  29), 
the  total  urinary  nitrogen  upon  the  several  days  of  the  experi- 
ment was :  — 

TABLE  30.  —  PROTEIN  KATABOLISM  OF  A  FASTING  MAN  —  BENEDICT 


URINARY  NITROGEN 

URINARY  NITROGEN 

Total 

Per  kilogram 
weight 

Total 

Per  kilogram 
weight 

Grams 

Grams 

Grams 

Grams 

I 

12.24 

0.206 

5 

10.87 

0.191 

2 

12.45 

.211 

6 

10.74 

.190 

3 

13.02 

.223 

7 

10.13 

.181 

4 

11.63 

.202 

Ztschr.  Biol.,  41  (1901),  167. 


252 


NUTRITION  OF  FARM   ANIMALS 


337.  Influence  of  body  fat.  —  E.  Voit's  compilation  (335) 
likewise  showed  clearly  that  the  ratio  of  protein  to  total  katab- 
olism  in  fasting  may  vary  considerably  as  between  individuals, 
depending  on  the  relative  amount  of  fat  contained  in  the  body. 
So  long  as  body  fat  is  readily  available  as  fuel,  the  amount  of 
protein  katabolized  remains  relatively  small,  but  if  the  animal  is 
originally  deficient  in  fat,  or  if  its  content  of  fat  becomes  much 
reduced  during  fasting,  more  protein  is  katabolized  to  make  up 
for  the  deficiency. 

Usually,  the  store  of  fat  in  the  body  is  less  than  that  of  protein, 
while  in  fasting  its  exhaustion  is  relatively  more  rapid.  There  comes 
a  time,  therefore,  when  the  supply  of  non-nitrogenous  material  to  the 
tissues  begins  to  flag.  When  this  happens,  the  protein  katabolism 
begins  to  increase ;  that  is,  when  the  supply  of  reserve  fuel  material 
runs  low,  the  organism  begins  to  use  more  of  the  protein  of  its  tissues 
as  a  source  of  energy,  and  Voit x  has  shown  that  this  occurs  whenever 
the  ratio  of  fat  to  protein  remaining  in  the  body  falls  below  a  certain 
limit.  If  the  animal  was  originally  well  nourished,  this  rise  in  the 
protein  katabolism  occurs  only  shortly  before  death,  from  which  it 
has  received  the  name  premortal  rise.  In  the  case  of  very  fat  ani- 
mals this  point  may  never  be  reached,  while,  on  the  other  hand,  in  a 
lean  animal  the  protein  katabolism  may  increase  steadily  from  the 
very  beginning  of  the  fasting.  The  following  three  experiments 
upon  a  fat  guinea  pig,  a  medium  fat  dog  and  a  lean  rabbit,  cited  by 
Voit  from  Rubner's  experiments,  serve  to  illustrate  these  three  types 
of  fasting  katabolism. 

TABLE  31.  —  FASTING  PROTEIN  KATABOLISM  OF  FAT,  MEDIUM  AND  THIN 

ANIMALS 


GUINEA  PIG 

DOG 

RABBIT 

Protein  Katab- 

Protein Ka- 

Protein Ka- 

Day of 

olism  in  Per  Cent 

Day  of 

tabolism  in  Per 

Day  of 

tabolism  in  Per 

Fasting 

of  Total  Katab- 
olism 

Fasting 

Cent  of  Total 
Katabolism 

Fasting 

Cent  of  Total 
Katabolism 

2 

10.4 

2-4 

16.3 

3 

I6.5 

3 

II.  I 

IO-II 

I3-I 

5-7 

23-6 

4 

II.O 

12 

15-5 

9-12 

26.5 

5 

II.Q 

13 

17.4 

I3-I5 

29.8 

6 

11.8 

14 

2O.O 

16 

50.1 

7 

6.9 

17-18 

96.4 

.      8 

II.  2 

9 

lO.Q 

1  Ztschr.  Biol.,  41  (1901),  502. 


THE   FASTING   KATABOLISM 


253 


338.  Influence  of  previous  protein  feeding.  —  The  classic 
experiments  of  Carl  Voit 1  upon  fasting  dogs  have  shown  that 
the  protein  katabolism  in  the  early  days  of  fasting  may  vary 
widely  according  to  the  amount  of  protein  previously  consumed. 
When  the  fasting  follows  a  high  protein  ration,  the  protein 
katabolism  on  the  first  day  of  fasting  may  be  relatively  large, 
but  it  soon  falls  to  a  comparatively  low  level  which  is  approxi- 
mately the  same  whatever  the  initial  ration.  This  behavior  is 
well  illustrated  by  the  following  results,  all  upon  the  same 
animal,  which  have  been  fully  confirmed  by  numerous  sub- 
sequent experiments. 


TABLE  32.  —  PROTEIN  KATABOLISM  OF  FASTING  DOG  —  VOIT 


PREVIOUS  FEEDING 

1800 

2500 

Grams 

1500 

1500 

Grams 

Meat, 

Grams 

Grams 

Bread 

Meat 

2  50  Grams 

Meat 

Meat 

Fat 

Grams 

Grams 

Grams 

Grams 

Grams 

Urinary  nitrogen  2  per  day 

Last  day  of  feeding       .     . 

84.4 

60.7 

51-7 

51-7 

"•5 

First  day  of  fasting  .     .     . 

28.1 

17-5 

13-9 

12.4 

9.1 

Second  day  of  fasting    .     . 

n.6 

10.9 

8-5 

8-7 

7-3 

Third  day  of  fasting      .     . 

8.9 

7-8 

8.2 

7-3 

7.0 

Fourth  day  of  fasting   .     . 

8.1 

6.9 

7.0 

7.0 

6.2 

Fifth  day  of  fasting       .     . 

5-7 

5-9 

6.6 

6.9 

5-9 

Sixth  day  of  fasting  .     .     . 

6.2 

6.0 

6.1 

6.0 

6.1 

Seventh  day  of  fasting  .     . 

5-8 

5-6 

5-6 

6.0 

Eighth  day  of  fasting    .     . 

4-7 

6.0 

5-6 

Ninth  day  of  fasting     .     . 

5-6 

Tenth  day  of  fasting     .     . 

5-3 

Furthermore,  the  high  protein  katabolism  which  is  observed 
during  the  first  two  or  three  days  of  fasting  after  high  protein 
feeding  is  accompanied  by  a  relatively  smaller  katabolism 
of  fat.  Thus,  in  the  first  of  the  foregoing  experiments  respira- 
tion trials  were  made  on  the  second,  fifth  and  eighth  days  with 
the  following  results :  — 


1  Ztschr.  Biol.,  2  (1866),  307. 


2  Computed  from  Voit's  figures  for  urea. 


254  NUTRITION  OF   FARM   ANIMALS 

TABLE  33.  —  TOTAL  KATABOLISM  OF  FASTING  DOG 


PROTEIN  KATAB- 

URINARY 

FAT  KATABO- 

OLISM  IN  PER 

NITROGEN 

LIZED 

CENT  OF  TOTAL 

KATABOLISM 

Grams 

Grams 

% 

Second  day     

n.6 

86 

26.2 

Fifth  day 

57 

IO3 

127 

Eighth  day     

4-7 

99 

ii.  i 

Obviously,  we  have  here  the  reverse  of  what  takes  place  in 
the  later  days  of  fasting,  viz.,  a  gradual  substitution  of  fat  for 
protein  as  the  readily  available  supply  of  the  latter  in  the  body 
is  reduced.  Doubtless  the  effect  would  have  been  found  to 
be  still  more  marked  on  the  first  day  of  fasting,  when  the  pro- 
tein katabolism  was  equivalent  to  28.1  grams  of  nitrogen. 

339.  Physiological  minimum  of  protein.  —  The  facts  re- 
corded in  the  previous  paragraphs  render  it  evident  that  the 
lowest  level  of  protein  katabolism  is  not  necessarily  attained 
during  complete  fasting.  Although  the  protein  katabolism  of 
a  fasting  animal  soon  reaches  a  comparatively  low  level  which 
changes  but  slowly,  nevertheless  its  amount  may  be  greatly 
affected,  on  the  one  hand  by  the  amount  of  protein  previously 
consumed,  and  on  the  other  hand  by  the  stock  of  non-nitrogenous 
material  (fat  and  glycogen)  contained  in  the  body.  While 
normally  some  10  to  17  per  cent  of  the  energy  metabolized 
in  complete  fasting  is  derived  from  protein  (335),  the  proportion 
may  rise  to  twice  this  amount  on  a  day  following  heavy  protein 
feeding,  or  to  almost  100  per  cent  in  case  of  an  animal  whose 
stock  of  body  fat  is  exhausted.  In  such  cases  it  is  evident  that 
part  of  the  protein  is  katabolized  simply  for  the  sake  of  supply- 
ing energy,  since  the  smaller  amounts  katabolized  in  what  may 
be  called  a  normal  or  average  condition  of  the  fasting  animal 
are  at  least  sufficient  to  maintain  all  the  vital  functions,  the 
latter  proceeding  for  a  considerable  time  in  a  substantially 
normal  manner. 

The  level  of  protein  katabolism  being  so  dependent  on  the 
amount  of  non-nitrogenous  material  available  as  a  source  of 
energy,  the  question  naturally  arises  whether  by  supplying  an 


THE  FASTING  KATABOLISM  255 

animal  with  liberal  amounts  of  non-nitrogenous  nutrients,  but 
no  protein,  the  protein  katabolism  might  not  be  reduced  to  an 
amount  even  smaller  than  that  observed  in  the  absence  of  all 
feed.  Experiments  by  C.  Voit  and  by  Rubner  on  dogs  and  by 
Landergren,  Folin  and  Cathcart  on  man  have  shown  this  to 
be  the  case  with  these  species. 

Comparisons  of  this  sort  on  farm  animals  are  not  readily 
made,  especially  with  herbivora,  and  none  have  yet  been  re- 
ported, but  McCollum  and  Steenbock  1  have  shown  that  the 
protein  katabolism  of  the  pig  may  be  reduced  by  long  continued 
feeding  on  a  non-nitrogenous  diet  (starch)  to  an  amount  materi- 
ally less  than  appears  to  be  necessary  in  the  feed  of  the  animal 
under  ordinary  conditions  to  maintain  nitrogen  equilibrium 
(417),  the  average  of  all  of  their  experiments  being  equivalent 
to  0.28  Ib.  of  protein  per  1000  Ibs.  live  weight. 

340.  Functions  of  protein  in  fasting.  —  The  fact  that  a 
certain  minimum  katabolism  of  body  protein  persists  even  in 
the  presence  of  the  most  abundant  supply  of  non-nitrogenous 
nutrients  has  generally  been  interpreted  in  the  past  as  showing 
that  a  certain  amount  of  the  protein  of  the  cell  is  necessarily 
broken  down  in  the  performance  of  its  physiological  functions. 
This  necessary  minimum  has  been  somewhat  vaguely  compared 
to  the  wear  of  a  machine,  Rubner  especially  designating  it  as 
the  "  wear  and  tear  "  quota  of  the  protein  katabolism.  More 
recent  investigations,  however,  have  suggested  the  possibility 
of  another  explanation. 

The  actual  nitrogenous  nutriment  of  the  body  cells  is  not 
proteins  as  such,  but  substantially  the  simple  amino  acids  out 
of  which  they  are  built  up.  As  required,  these  amino  acids 
may  be  synthesized  to  protein  (226,  232),  but  thqre  appears  to 
be  some  reason  for  believing  that  they  may  also  be  necessary 
for  other  purposes  in  the  body ;  that  certain  of  them  may,  for 
example,  as  was  suggested  by  Willcock  and  Hopkins,  be  essential 
to  the  production  of  the  various  internal  secretions  and  hormones 
which  apparently  play  so  large  a  part  in  metabolism.  If,  how- 
ever, the  normal  performance  of  the  body  functions  calls  for 
a  supply  of  some  particular  amino  acid,  tryptophan  e.g.,  this 
can  be  derived,  in  the  fasting  animal,  only  from  the  cleavage  of 
body  protein,  since  there  is  no  evidence  that  tryptophan  can 

1  Wis.  Expt.  Sta.,  Research  Bui.  No.  21,  p.  55. 


256  NUTRITION  OF  FARM  ANIMALS 

be  synthesized  by  the  organism.  It  might  very  well  be,  there- 
fore, that  the  minimum  unavoidable  protein  katabolism  in  the 
absence  of  nitrogenous  feed  is  due  to  such  a  demand  for  certain 
amino  acids  or  other  groupings,  and  only  in  part  or  not  at  all 
to  a  necessary  breaking  down  of  cell  proteins  as  a  condition  of 
protoplasmic  activity.  Moreover,  it  is  quite  conceivable  that 
both  of  these  views  may  be  true ;  that  a  part  of  the  minimum 
protein  katabolism  represents  a  necessary  destruction  of  cell 
protoplasm  in  the  performance  of  its  functions,  while  the  other 
part  represents  protein  broken  down  for  the  sake  of  securing 
certain  constituents  for  specific  purposes. 

There  will  be  occasion  to  consider  these  possibilities  further 
in  discussing  the  protein  requirement  for  maintenance  (398). 

§  2.    THE  ENERGY  KATABOLISM  IN  FASTING 

341.  Internal  work.  —  The  body  of  an  animal  receiving  no 
feed  and  doing  no  external  work  is  still  carrying  on  a  great 
variety  of  internal  activities,  both  mechanical  and  chemical. 
Of  the  former,  the  most  prominent  is  the  muscular  work  of 
circulation   and   respiration,    together   with    the   maintenance 
of  muscular  tonus   (632),   while   the  secretory  and  excretory 
activities  of  the  various  glands  are  typical  of  the  latter.     These 
various  bodily  activities,  whose  due  performance  is  essential 
to  the  continued  existence  of  the  animal,  may  be  conveniently 
summarized  in  the  term  internal  work. 

342.  Measure  of  energy  expended  in  internal  work.  —  In 
the  fasting  animal,  all  the  various  forms  of  internal  work  in- 
dicated in  the  previous  paragraph  are  performed  by  means  of 
energy  derived  from  the  katabolism  of  the  fats,  carbohydrates 
and  proteins  contained  in  the  tissues.     The  chemical  energy 
thus    utilized    may    undergo    numerous    transformations,  but 
ultimately,  since  it  does  no  work  upon  the  surroundings  of  the 
animal,  it  assumes  the  form  of  heat.     A  determination  of  the 
heat  produced  by  a  fasting  animal  in  a  state  of  rest,  therefore, 
furnishes  a  measure  of  the  energy  expended  in  internal  work, 
or  of  what  is  often  called  the  basal  metabolism. 

343.  Relative  constancy  of  energy  katabolism.  —  The  results 
recorded  in  §  i  regarding  the  nature  of  the  material  katabolized 
in  fasting,  and  the  way  in  which  fat,  carbohydrates  and  protein 


THE  FASTING  KATABOLISM 


257 


may  mutually  replace  each  other  as  fuel  material  according  as 
one  or  the  other  is  most  available,  render  it  evident  that  the 
controlling  factor  in  the  katabolism  of  the  fasting  body  is  the 
demand  for  energy  for  the  performance  of  the  internal  work  and 
can  hardly  have  failed  to  suggest  that  this  demand  must  be 
relatively  constant  in  the  same  individual  under  like  conditions. 
That  such  is  in  fact  the  case  has  been  demonstrated  by  a  large 
number  of  experiments.  While  not  mathematically  invariable, 
the  fasting  katabolism,  expressed  in  terms  of  energy,  tends 
to  approach  a  uniform  value  in  proportion  as  the  experimental 
conditions  are  maintained  constant.  The  fasting  organism 
requires  approximately  the  same  quantity  of  energy  from  day 
to  day  for  the  performance  of  its  necessary  internal  work,  but 
seems  more  or  less  indifferent  as  to  whether  this  energy  is 
derived  from  the  katabolism  of  fats,  carbohydrates'  or  proteins. 

For  example,  in  Voit's  experiment  cited  in  the  previous  section  to 
illustrate  the  interrelations  of  protein  and  fat  katabolism  (Table  33), 
the  computed  energy  of  the  protein  and  fat  katabolized  on  each  of 
the  three  days  was  as  shown  in  the  following  table,  from  which  it 
appears  that  the  total  energy  katabolism,  especially  when  computed 
per  kilogram  of  live  weight,  was  approximately  the  same  on  the 
different  days. 

TABLE  34.  —  ENERGY  KATABOLISM  OF  FASTING  DOG 


TOTAL 

LIVE 
WEIGHT 

ENERGY 

FROM 

PROTEIN 

ENERGY 

FROM 

FAT 

TOTAL 
ENERGY 

ENERGY 
PER  KG. 
LIVE 

WEIGHT 

Kgs. 

Cals. 

Cals. 

Cals. 

Cals. 

Second  day       

32.87 

289.3 

816.9 

1106.2 

33-66 

Fifth  day     

31.67 

142.2 

978.5 

1120.7 

35.38 

Eighth  day  

30-54 

117.2 

942.4         1059.6 

34-70 

The  same  thing  is  true  of  Rubner's  determinations  of  the  fasting 
katabolism  of  a  rabbit,  a  dog  and  a  guinea  pig,  whose  results  as  re- 
gards the  protein  katabolism  have  been  already  considered  (337)  and 
likewise  of  Benedict's  investigations  upon  fasting  men  (334). 

344.  Energy  expenditure  in  fasting  a  measure  of  main- 
tenance requirement.  —  In  the  fasting  animal  in  a  state  of 


258  NUTRITION  OF  FARM  ANIMALS 

complete  rest  and  at  moderate  external  temperature,  the  vital 
activities  are  evidently  reduced  to  the  minimum  compatible 
with  the  continuance  of  life.  Since  the  internal  work  of  such 
an  animal  is  performed  at  the  expense  of  the  chemical  energy 
stored  up  in  its  tissues,  the  body's  stock  of  energy  is  being 
constantly  depleted  by  an  amount  equivalent  to  the  internal 
work  done  and  this  loss  of  energy  must  be  made  good  from  the 
feed  if  the  animal  is  to  be  maintained.  The  relatively  constant 
total  katabolism  of  the  fasting  animal,  as  expressed  in  its  heat 
production,  is  therefore  the  measure  of  the  amount  of  energy 
expended  in  carrying  on  the  fundamental  vital  activities  of 
the  body,  and  consequently  of  the  minimum  quantity  which  must 
be  supplied  in  a  maintenance  ration. 

§  3.    CONDITIONS  AFFECTING  THE  FASTING  KATABOLISM 

345.  Size  of  animal.  —  That  large  animals  katabolize  more 
matter  and  produce  more  heat  than  smaller  ones,  and  therefore 
require  more  feed  for  maintenance,  needs  no  special  proof.    Ex- 
periment shows,  however,  that  the  difference  is  not  propor- 
tional to  size  or  weight,  but  that  small  animals  have  a  more 
intense  katabolism  than  large  ones,  its  amount  being  approxi- 
mately proportional  to  the  body  surface,  which,  of  course,  is 
relatively  greater  in  the  smaller  animal. 

The  relation  to  body  surface  appears  to  have  been  first  suggested 
by  Bergmann  (cited  by  Rubner)  in  1852  and  later  by  Miintz  l  in  1878, 
but  Rubner  2  seems  to  have  made  the  first  quantitative  investigation 
of  the  question,  determining  the  fasting  katabolism  of  six  dogs  whose 
weights  ranged  from  3  to  24  kilograms. 

While  not  mathematically  constant,  the  ratio  between  the  fasting 
katabolism  and  surface  showed  a  close  approximation  to  uniformity, 
and  the  same  fact  has  been  verified  by  a  considerable  number  of  in- 
vestigators, although  with  some  exceptions,  and  is  now  generally  ac- 
cepted. Moreover,  it  has  been  shown 3  to  be  approximately  true  not 
only  of  animals  of  the  same  species  but  of  animals  ranging  in  size 
from  man  to  domestic  fowls  and  including  also  cold  blooded  animals. 

346.  Computation  of  katabolism  per  unit  of  surface.  —  It 
is  a  familiar  fact  that  the  surfaces  of  solids  of  the  same  shape, 

1  Ann.  Inst.  Agron.,  Ill,  p.  59.  2  Ztschr.  Biol,  19  (1883),  535. 

3E.  Voit;  Ztschr.  Biol.,  41  (1901),  113. 


THE   FASTING  KATABOLISM  259 

i.e.,  of  those  which  are  geometrically  similar  figures,  are  propor- 
tional to  the  two-thirds  powers  of  their  volumes.  Since  the 
specific  gravity  of  animals  varies  but  slightly,  it  may  be  said 
without  material  error  that  the  body  surfaces  of  animals  of  the 
same  shape  are  proportional  to  the  two-thirds  powers  of  their 
weights.  This  relation  may  be  expressed  by  the  following  for- 
mula,, proposed  by  Meeh,1  in  which  W  equals  the  weight  in 
grams,  S  the  surface  in  square  centimeters,  and  k  is  a  factor 
which  is  constant  for  all  animals  of  the  same  shape. 

S  =  kW\ 

The  value  of  the  constant  k  for  the  horse  as  reported  by 
Hecker  is  9.02.  Trowbridge,  Moulton  and  Haigh  2  have  de- 
termined the  value  of  k  for  35  Hereford-Shorthorn  cattle  of 
various  ages  from  birth  up  and  in  various  conditions  of  fatness, 
using  the  empty  weight  as  a  basis.  Dividing  the  animals  into 
groups  they  found  the  following  average  values :  — 

TABLE  35.  —  VALUES  OF  k  FOR  BEEF  CATTLE 

Young  and  thin  animals 9.92 

Animals  in  medium  condition 9.41 

Fat  animals  18  months  old  or  less 8.57 

Fat  animals  two  years  old  or  more 7.65 

According  to  these  investigators  the  empty  weight  of  cattle 
constitutes  the  following  percentages  of  their  live  weight :  — 

TABLE  36.  —  EMPTY  WEIGHT  AS  PERCENTAGE  OF  LIVE  WEIGHT 

Show  cattle 92-94  per  cent 

Fat  cattle 91 

Medium  cattle 89-90 

Thin  cattle 87-89 

With  the  aid  of  the  foregoing  factors  the  total  katabolism 
of  beef  cattle,  and  perhaps  of  other  types,  as  determined  by 
experiment  may  be  computed  per  unit  of  body  surface  with 
reasonable  accuracy.  It  is  apparent  that  comparisons  based 
upon  the  live  weight  instead  of  the  empty  weight  would  also 
be  substantially  accurate  for  thin  and  medium  cattle.  No 
similar  data  exist  for  other  species  of  farm  animals. 

1  Ztschr.  Biol.,  15  (1879),  425.  2  Mo.  Expt.  Sta.,  Research  Bui.  18. 


260  NUTRITION  OF  FARM.  ANIMALS 

The  principal  cause  of  the  difference  between  the  groups  of  cattle 
appears  to  be  the  variation  in  the  proportion  of  fat  to  active  tissue, 
and  Moulton  1  has  shown  that  if  this  be  eliminated  by  making  the 
fat-free  empty  weight  the  basis  of  computation,  an  average  value  of 
10.34  for  k  gives  results  very  closely  approximating  those  actually 
observed.  He  likewise  finds  that  the  body  surface  of  thin  and  medium 
cattle  is  somewhat  more  closely  proportional  to  the  five-eighths  than 
to  the  two-thirds  power  of  the  empty  weight,  while  for  fat  cattle  the 
five-ninths  power  gives  the  closest  agreement,  the  corresponding 
values  of  k  being  respectively  n.86  and  13.40. 

347.  Computation  of  katabolism  to  standard  weight.  —  It 
is  often  desirable  to  compare  the  katabolism  of  animals  of  dif- 
ferent weights  or  to  compute  experimental  results  to  some 
convenient  standard  weight.  Such  comparisons  should  evi- 
dently be  made  on  the  basis  of  body  surface  rather  than  of  body 
weight.  Few  actual  determinations  of  the  body  surface  of 
animals  have  been  made,  however,  and  with  the  exception  of 
the  horse  and  of  beef  cattle  none  on  farm  animals,  so  that  it  is 
in  many  cases  impracticable  to  .express  the  katabolism  of  the 
latter  per  unit  of  surface.  For  purposes  of  comparison  between 
individuals  of  the  same  species  and  type,  however,  at  least 
approximate  results  may  be  secured  on  the  assumption  that 
the  animals  to  be  compared  are  geometrically  similar,  so  that 
their  body  surfaces  are  substantially  proportional  to  the  two- 
thirds  powers  of  their  weights.  For  example,  a  steer  weighing 
1283  pounds  was  found  to  have  a  computed  fasting  katabolism 
(374)  of  8671  Cals.  It  is  often  a  matter  of  convenience  to  com- 
pute such  a  result  to  a  weight  of  1000  pounds.  A  steer  weigh- 
ing 1000  pounds,  other  things  being  equal,  would  have  a  smaller 
katabolism  in  proportion  to  its  smaller  surface.  The  ratio 
between  the  surfaces  of  the  two  animals  would  be  approximately 
looo*:  1283%  and  the  fasting  katabolism  of  the  smaller  animal 
would  therefore  be  8671  Cals.  X  (jiif)!  =  7345  Cals.  In 
this  way  it  is  easy  to  compute  the  relative  katabolism  of  dif- 
ferent individuals  without  the  necessity  of  expressing  it  per 
unit  of  surface. 

Of  course,  such  a  comparison  is  only  an  approximation.  In 
particular,  as  has  just  been  shown  (346),  different  animals  are 
not  of  the  same  shape.  The  young  animal  differs  in  conforma- 

1  Jour.  Biol.  Chem.,  24  (1916),  299. 


THE  FASTING   KATABOLISM  261 

tion  from  the  older  one  and  the  fat  from  the  thin  one  and  the 
beef  steer  and  dairy  cow,  e.g.,  are  far  from  being  geometrically 
similar.  Additional  determinations  of  the  relation  of  surface 
to  weight  in  different  species,  types  and  ages  of  domestic  ani- 
mals would  be  of  much  interest  but  in  their  absence  the  method 
of  comparison  just  outlined  may  probably  be  assumed  to  give 
a  fair  approximation  to  the  truth  and  is  certainly  more  accurate 
than  a  simple  computation  in  proportion  to  weight. 

348.  Muscular  activity.  —  As  was  implied  in  the  introductory 
section  of  Chapter  VI  (274),  and  as  will  appear  in  greater  detail 
in  Chapter  XIV,  muscular  work  is  done  at  the  expense  of  energy 
derived  from  the  katabolism  of  body  substance,  and  no  other 
single  factor  so  largely  influences  the  total  katabolism.  The 
minimum  fasting  katabolism  which  represents  the  demands  of 
the  indispensable  life  processes  is  exhibited  only  ifl  a  state  of 
complete  muscular  rest.  It  is  rarely  the  case,  however,  that  an 
animal,  even  when  at  rest  in  the  ordinary  sense,  does  not  main- 
tain more  or  less  muscular  tension  or  execute  more  or  less  mo- 
tions of  various  parts  of  the  body,  all  of  which,  even  when 
apparently  slight,  involve  in  the  aggregate  considerable  ex- 
penditure of  energy. 

Zuntz  and  Hagemann,1  for  example,  report  a  respiration  experiment 
upon  a  horse  in  which  the  uneasiness  caused  by  the  presence  of  a  few 
flies  in  the  chamber  of  the  apparatus  caused  an  increase  of  10  per 
cent  in  the  metabolism.  Johansson  2  found  the  hourly  excretion  of 
carbon  dioxid  by  a  fasting  man  when  simply  lying  in  bed  (awake) 
to  be  24.94  grams  as  compared  with  20.72  grams  when  all  the  muscles 
were  as  perfectly  relaxed  as  possible.  Benedict  and  Carpenter  3  have 
compared  the  metabolism  of  men  during  sleep  with  that  of  the  same 
subjects  lying  quietly  in  bed  immediately  after  waking.  In  the  three 
cases  which  they  regard  as  strictly  comparable  the  increase  in  the 
heat  production  during  the  waking  period  ranged  from  5.8  to  15.2 
per  cent,  averaging  11.4  per  cent.  Benedict  and  Talbot,4  in  experiments 
upon  infants,  found  that  even  scarcely  noticeable  muscular  activity 
produced  a  most  marked  effect  on  the  carbon  dioxid  excretion,  and 
Benedict  and  Pratt  5  have  noted  similar  results  with  dogs. 


.  Jahrb.,  23  (1894),  161. 

2  Skand.  Arch.  Physiol.,  8  (1898),  85. 

3  Carnegie  Institution  of  Washington,  Publication  No.  126  (1910),  p.  241. 

4  Amer.  Jour.  Diseases  of  Children,  4  (1912),  129. 
6  Jour.  Biol.  Chem.,  15  (1913),  i. 


262  NUTRITION  OF  FARM  ANIMALS 

Since  comparatively  insignificant  movements  have  such  a 
striking  effect  upon  the  total  katabolism,  it  is  evident  that  the 
amount  of  muscular  activity  must  be  an  important  factor  in 
determining  the  relative  energy  requirements  of  two  animals 
even  though  their  minimum  katabolism  in  a  state  of  absolute 
rest  may  be  identical.  In  experiments  of  any  considerable 
duration  on  normal  animals,  it  is  impossible  to  avoid  more  or 
less  expenditure  of  energy  in,  this  incidental  muscular  work, 
while  it  is  often  a  matter  of  difficulty  to  make  the  different 
periods  of  an  experiment  comparable  in  this  respect. 

349.  Standing  and  lying.  —  Considerable  muscular  exertion 
is  required  during  the  waking  hours  to  maintain  the  relative 
position  of  the  different  members  of  the  body.     This  is  es- 
pecially true  of  standing.     It  has  been  shown  that  a  man  or  an 
animal  when   standing  excretes  notably  more  carbon    dioxid 
than  when  resting  or  lying  down  and  produces  correspondingly 
more  heat.     Differences  of  as  much  as  25  per  cent  have  been 
observed  in  man  and  of  30  to  40  or  more  per  cent,  in  cattle.     It 
is  evident,  then,  that  if  one  animal  lies  down  for  twelve  hours 
and  another  for  only  eight  hours  during  the  twenty-four,  the 
former  will,  other  things  being  equal,  require  less  feed  energy 
for  actual  maintenance  than  the  latter. 

350.  External  temperature.  —  Farm  animals  belong  to  that 
general  class  known  as  warm  blooded,  or  homoiothermic,  animals, 
whose  bodies  during  health  maintain  a  nearly  constant  tempera- 
ture which  is  higher  than  that  of  their  usual  surroundings.     The 
so-called  "  animal  heat  "  is  being  continually  generated  by  the 
katabolism  going  on  in  the  body,  while  on  the  other  hand  the 
animal  is  continually  imparting  heat  to  its  surroundings  in  four 
principal  ways:  viz.,  by  conduction,  by  radiation,  by  evapora- 
tion of  water,  and  as  the  sensible  heat  of  the  excreta. 

Since  the  animal  is  both  producing  and  losing  heat  continu- 
ally, the  maintenance  of  a  constant  body  temperature  implies 
the  existence  of  some  regulative  mechanism  by  means  of  which 
the  production  and  emission  of  heat  may  be  adjusted  to  each 
other.  This  adjustment  is  effected  in  general  in  two  ways  which 
may  be  called,  respectively,  physical  and  chemical  regulation. 

351.  Physical  regulation  of  body  temperature.  —  Changes 
in  the  temperature  of  its  surroundings,  in  the  relative  humidity 
of  the  air,  etc.,  tend  to  produce  the  same  effect  upon  the  animal 


THE  FASTING  KATABOLISM  263 

as  upon  an  inanimate  body.  A  fall  of  temperature,  for  example, 
tends  to  increase  the  rate  of  outflow  of  heat  and  a  rise  of  tem- 
perature to  diminish  it.  In  the  so-called  physical  regulation, 
these  tendencies  are  offset  and  the  rate  of  heat  emission  main- 
tained constant  chiefly  by  means  of  changes  in  the  temperature 
and  state  of  moisture  of  the  skin,  brought  about  on  the 'one 
hand  by  an  adjustment  of  the  blood  flow  and  on  the  other 
through  the  perspiration. 

The  tendency  of  a  rise  of  external  temperature  to  check 
the  outflow  of  heat  is  compensated  for  by  a  vaso-motor  reflex 
which  causes  the  arterioles  leading  to  the  surface  of  the  body  to 
relax  (187),  so  that  more  blood  flows  through  the  skin  capillaries, 
thus  tending  to  raise  the  temperature  of  the  surface  and  increase 
the  outflow  of  heat.  This  phenomenon  is  readily  observed 
in  the  flush  which  follows  exposure  to  high  temperatures.  This 
method  of  regulation  might  be  compared  to  opening  the  win- 
dows of  a  heated  room  to  cool  it. 

If  the  external  temperature  continues  to  rise,  visible  per- 
spiration occurs,  or  in  the  case  of  animals  which  have  no  sweat 
glands,  like  the  dog,  a  peculiar  form  of  breathing  sets  in  and 
relatively  large  amounts  of  water  are  evaporated  from  the  skin 
or  from  the  tongue  and  the  interior  of  the  mouth  and  throat. 
In  this  way,  large  quantities  of  heat  are  carried  off  as  the  latent 
heat  of  vaporization  of  water,  somewhat  as  an  overheated  room 
may  be  cooled  by  sprinkling  the  floor. 

If  the  external  temperature  falls  again,  the  process  is  reversed. 
Sensible  perspiration  decreases,  the  blood  is  diverted  from  the 
capillaries  of  the  skin  to  the  internal  capillaries,  and  if  the  change 
takes  place  too  rapidly,  may  even  lead  to  congestion  of  the  latter. 
The  .process  is  analogous  to  closing  the  windows  of  a  room  as 
the  weather  grows  colder. 

352.  Chemical  regulation  of  body  temperature.  —  There 
are  evidently  limits  to  the  possibilities  of  physical  regulation. 
On  the  one  hand,  the  external  temperature  may  rise  so  high 
that  it  is  impossible  for  the  heat  to  escape  from  the  body  as  fast 
as  it  is  produced  by  the  necessary  katabolism,  and  heat  apoplexy 
results.  On  the  other  hand,  the  temperature  may  fall  so  low 
that  the  utmost  restriction  of  evaporation  and  the  greatest 
possible  diversion  of  the  blood  from  the  superficial  capillaries 
is  insufficient  to  conserve  the  body  temperature.  If  the  windows 


264  NUTRITION  OF  FARM  ANIMALS 

of  the  room  are  entirely  closed,  nothing  more  can  be  effected 
in  this  manner  toward  maintaining  its  temperature,  and  if  the 
weather  continues  to  grow  colder,  the  fire  in  the  room  must  be 
increased.  Similarly,  if  the  external  cooling  effect  upon  the 
animal  becomes  so  great  as  to  exceed  the  limits  of  physical  ad- 
justment, more  fuel  material  is  katabolized,  that  is,  more  heat 
is  produced.  This  method  of  maintaining  the  body  temperature 
is  commonly  called  chemical  regulation. 

353.  Mechanism    of    chemical   regulation.  —  The    chemical 
regulation  is  probably  effected  largely  through  muscular  action, 
by  visible  motion  or  by  an  increase  in  the  muscular  tonus, 
either  of  which  involves  an  increased  heat  production.     This 
has  been  clearly  shown  to  be  true  of  man  and  probably  applies 
also  to  other  animals.     Above  the  critical  temperature,  there 
appears  to  be  a  slight  increase  in  the  heat  production  with 
rising  temperature,  probably  due  to  the  additional  energy  ex- 
pended in  the  various  processes  of  physical  regulation. 

354.  Critical  temperature.  —  The  temperature  at  which  the 
physical  regulation  gives  way  to  or  begins  to  be  supplemented 
by  the  chemical  regulation  has  been  called  the  critical  tempera- 
ture.1   Above  this  temperature  the  radiating  capacity  of  the 
body '  surf  ace  is  varied  to  meet  the  varying  conditions;  below 
it,  this  method  of  regulation  is  largely  exhausted  and  therefore 
the  heat  production  is  varied  to  meet  the  need.     The  critical 
temperature  for  man  wearing  ordinary  clothing  appears  to  be 
about  15°  C. ;  for  the  dog  it  is  about  20°  C.,  for  the  guinea  pig 
3o°-35°,  and  for  the  hog,  according  to  the  results  of  Tangl 2 
and  of  Von  der  Heide  and  Klein,3  about  2o°-23°  C. 

355 .  O ther  thermal  conditions .  —  Any  conditions  tending  to  facili- 
tate the  escape  of  heat  from  the  body  will  obviously  act  like  a  fall  of 
temperature.     Wind,  for  example,  by  removing  the  layer  of  partially 
warmed  air  next  to  the  skin,  tends  to  remove  heat  more  rapidly  from 
the  body,  so  that  the  cold  is  felt  more  severely  on  a  windy  day,  while, 
on  the  other  hand,  the  effect  of  a  high  temperature  is  modified  by 
wind.     A  high  percentage  humidity  of  the  air  on  a  warm  day  hinders 
the  removal  of  heat  by  evaporation,  so  that  a  moist  heat  is  more  try- 
ing than  a  dry  heat.     Cold  moist  air,  on  the  other  hand,  facilitates 

1  The  term  refers,  of  course,  to  the  temperature  of  the  surroundings  and  not  to 
that  of  the  animal  itself. 

2Biochem.  Ztschr.,  44  (1912),  252.  3  Ibid.,  55  (1913),  195- 


THE   FASTING   KAT ABOLISH  265 

the  escape  of  heat  from  the  body  by  increasing  the  conducting  power 
of  the  clothing,  hair  or  fur,  so  that  a  damp  cold  is  more  severe  than 
a  dry  cold.  The  direct  rays  of  the  sun  may  impart  a  considerable 
amount  of  heat  to  the  body,  thus  moderating  the  effects  of  low  tem- 
peratures and,  on  the  other  hand,  increasing  those  of  high  tempera- 
tures. To  be  strictly  accurate,  then,  one  should  speak  of  a  critical 
thermal  environment  of  the  animal  rather  than  simply  of  a  critical 
temperature. 

356.  Influence  on  katabolism.  —  It  is  apparent  from  the 
foregoing  facts  that  the  energy  katabolism  of  the  fasting  animal 
is  affected  by  the  external  temperature  and  other  thermal  con- 
ditions to  a  considerably  less  extent  than  has  been  frequently 
imagined.  It  is  by  no  means  true  that  every  fall  in  external 
temperature  results  in  an  increased  katabolism  in  the  animal 
for  the  sake  of  heat  production,  for  if  this  were  the  case  the  con- 
verse would  also  be  true,  viz.,  that  every  rise  in  the  external 
temperature  would  cause  a  corresponding  decrease  in  the  katab- 
olism, so  that  finally,  when  the  external  temperature  was 
equivalent  to  that  of  the  body,  the  katabolism  would  be  reduced 
to  zero ;  that  is,  we  should  have  life  without  katabolism,  which 
is  a  contradiction  in  terms. 

The  fact  that  the  heat  production  of  an  animal  reaches  a 
minimum  at  the  critical  temperature  and  that  above  that  point 
it  either  remains  unchanged  or  increases  slightly  shows  that  its 
extent  is  not  determined  by  the  needs  of  the  organism  for  heat 
as  such,  since  these  diminish  as  the  temperature  rises.  As  a 
matter  of  fact,  the  production  of  heat  in  the  body  is  not  the 
purpose  of  katabolism  but  merely  an  incident  of  it.  Heat  is 
the  form  which  the  chemical  energy  of  the  katabolized  material 
takes  after  it  has  served  its  purposes  in  the  vital  processes,  and 
the  nearly  constant  heat  production  above  the  critical  tem- 
perature is  simply  due  to  the  fact  that  the  quantity  of  energy 
required  for  the  internal  work  of  the  body  is  approximately 
constant  and  cannot  be  reduced  simply  by  raising  the  external 
temperature.  Heat  is  essentially  an  excretum  to  be  gotten  rid 
of.  Incidentally,  in  warm-blooded  animals,  it  serves  also  to 
maintain  the  body  temperature  necessary  for  the  normal  per- 
formance of  the  vital  functions,  but  above  the  critical  tempera- 
ture there  is  a  surplus  over  the  amount  required  for  this 
purpose  which  is  disposed  of  by  the  processes  of  physical  regu- 


266  NUTRITION  OF   FARM  ANIMALS 

lation  already  described.  It  is  only  when  the  external  tem- 
perature sinks  below  this  point  that  the  katabolic  processes 
are  stimulated  and  more  heat  is  produced,  and  only  below  this 
point,  therefore,  does  the  external  temperature  influence  the 
energy  requirement. 

357.  Effects  of  extremes  of  temperature.  —  The  regulation  of 
body  temperature  described  in  the  foregoing  paragraph  is  possible 
only  within  certain  limits. 

At  very  low  temperatures  the  possibilities  of  chemical  regulation 
may  be  exhausted,  so  that  the  animal  is  unable  to  produce  heat  as 
fast  as  it  is  abstracted  and  the  body  temperature  begins  to  fall.  An 
actual  lowering  of  the  body  temperature,  however,  reduces  the  inten- 
sity of  the  katabolism  exactly  as  it  does  in  the  case  of  a  cold-blooded 
animal ;  the  heat  production  sinks,  bringing  about  a  further  fall  in 
body  temperature  which  again  further  diminishes  the  heat  production, 
so  that  the  animal  speedily  perishes  from  cold. 

At  very  high  temperatures  the  reverse  process  'may  take  place. 
When  the  possibilities  of  physical  regulation  are  exhausted,  the  body 
temperature  rises.  A  very  slight  rise,  however,  has  been  shown  to 
stimulate  the  katabolism  and  therefore  the  heat  production,  giving 
rise  to  a  "vicious  circle"  which  is  the  converse  of  that  occurring  at 
very  low  temperatures  and  which  speedily  leads  to  the  animal  being 
overcome  by  heat. 


CHAPTER  VIII 
MAINTENANCE  — THE  ENERGY   REQUIREMENTS 

358.  Definition  of  maintenance.  —  Feed  is  supplied  to  farm 
animals  either  that  they  may  yield  products  useful  to  man  as 
materials  for  human  food  and  clothing  or  that  they  may  serve 
him  by  the  performance  of  mechanical  work. 

But  much  as  a  factory  must  first  be  supplied  with  enough 
power  to  keep  in  motion  the  shafting,  belting  and  machinery 
in  general  before  any  product  can  be  turned  out,  so  the  animal 
mechanism  must  be  provided  with  sufficient  feed  to  maintain 
the  processes  essential  to  life  before  any  continued  production 
is  possible.  The  amount  required  for  this  purpose  is  called 
the  maintenance  ration  of  the  particular  animal.  It  is  the 
quantity  necessary  simply  to  support  the  animal  when  doing 
no  work  and  yielding  no  material  product.  A  balance  experi- 
ment with  an  animal  receiving  precisely  a  maintenance  ration 
would  reveal  an  exact  equality  between  income  and  outgo  of 
ash,  nitrogen,  carbon,  hydrogen  and  energy,  showing  that  the 
body  was  neither  gaining  nor  losing  protein,  fat,  carbohydrates 
nor  mineral  elements.  From  this  point  of  view,  maintenance 
might  be  characterized  as  a  state  of  labile  equilibrium  between 
the  anabolic  and  katabolic  processes  of  metabolism  (203). 

The  word  maintenance  is  sometimes  used  popularly  in  an- 
other sense  to  signify  the  total  amount  of  feed  required,  for 
example,  by  a  horse  in  order  to  perform  his  daily  work  or  by  a 
calf  in  order  to  make  a  normal  growth.  It  is  important  to  grasp 
the  idea  that,  in  its  technical  sense,  the  maintenance  ration 
means  the  minimum  required  simply  to  maintain  life.  The 
total  feed  of  the  horse  or  calf  would,  from  this  point  of  view,  be 
regarded  as  consisting  of  two  portions ;  one  of  them  the  main- 
tenance ration,  which  if  fed  by  itself  would  just  support  the 
horse  at  rest  or  the  calf  without  growth,  and  the  other  the 
productive  portion  of  the  ration,  by  means  of  which  work  is 

267 


268  NUTRITION  OF   FARM  ANIMALS 

done  or  growth  made.  To  recur  to  the  illustration  of  the  fac- 
tory, the  maintenance  ration  keeps  the  empty  machinery 
running,  while  the  additional  feed  furnishes  the  power  neces- 
sary to  turn  out  the  finished  product. 

359.  Significance  of  the  maintenance  ration  in  practice.  — 
It  might  seem  at  first  thought  that  not  much  importance  at- 
taches  to  a  determination  of  the  maintenance  ration.     The 
animal  kept  on  such  a  ration  yields  no  direct  economic  return 
and  hence  simple  maintenance  feeding  is  to  be  avoided,  so  far 
as  possible,  while  if  it  appears  desirable  to  practice  it  the  ob- 
servation of  the  skilled  stockman,  especially  if  supplemented 
by  occasional  weighings,  will  usually  suffice  to  determine  whether 
or  not  the  end  is  being  attained.     Nevertheless,  the  subject  has 
much  significance  both  for  practice  and  for  science. 

A  very  considerable  fraction  of  the  feed  actually  consumed 
by  farm  animals  —  on  the  average  probably  fully  one-half  — 
is  required  simply  for  maintenance.  But  if  half  of  the  farmer's 
feed  bill  is  expended  for  maintenance,  it  is  clearly  important 
for  him  to  know  something  of  the  laws  of  maintenance,  —  how 
its  requirements  vary  as  between  different  animals,  how  they 
are  affected  by  the  conditions  under  which  animals  are  kept, 
how  different  feeding  stuffs  compare  in  value  for  maintenance, 
etc.,  —  as  well  as  to  understand  the  principles  governing  the 
production  of  meat,  milk,  or  work  from  the  other  half  of  his 
feed. 

360.  Bearing  on  interpretation  of  feeding    experiments.  — 
From  the  point  of  view  of  the  experimenter  a  knowledge  of 
the  maintenance  requirement  is  likewise  of  great  importance. 
In  any  rational  study  of  the  laws  of  nutrition,  it  is  plainly 
inadmissible  to  attempt  to  establish  general   principles   by   a 
comparison  of  the  feed  with  one  of  its  effects,  viz.,  production, 
while    ignoring    entirely    its    other    effect,    viz.,    maintenance. 
Failure  to  appreciate  this  fact  is  responsible  for  many  mislead- 
ing deductions  from  feeding  experiments  in  the  past. 

It  has  been  quite  usual  to  compare  the  results  of  such  experi- 
ments by  computing  the  ratio  of  feed  consumed  to  product 
yielded  —  i.e.,  either  the  feed  consumed  per  pound  of  gain 
made  or  the  gain  produced  per  pound  of  feed  consumed.  Such 
a  comparison,  however,  may  give  an  entirely  distorted  idea  of 
the  real  teachings  of  an  experiment.  Suppose,  for  example, 


MAINTENANCE  —  THE  ENERGY  REQUIREMENTS     269 

that  in  a  fattening  experiment  the  quantities  of  two  different 
rations  consumed  and  the  gains  made  were  as  follows :  — 

FIRST  RATION          SECOND  RATION 

Feed  eaten 18.0  Ib.  21.0  Ib. 

Daily  gain i.o  Ib.  1.5  Ib. 

Compared  in  the  way  just  indicated,  the  feed  required  to  pro- 
duce one  pound  of  gain  was  18  pounds  and  14  pounds  respectively, 
or  the  second  ration  appears  to  have  been  superior  to  the  first 
by  about  29  per  cent.  If,  however,  it  was  found  that  in  each 
case  12  pounds  of  the  feed  were  required  simply  to  maintain 
the  animal,  a  very  different  comparison  is  obtained,  viz. :  — 

FIRST  SECOND 

RATION         RATION 

Lb.  Lb. 

Feed  eaten       ,  18.0  21.0 

Expended  in  maintenance 12.0  12.0 

Surplus  left  for  production     . 6.0  9.0 

Daily  gain i.o  1.5 

Surplus  feed  per  pound  of  gain ,  6.0  6.0 

The  real  value  of  the  two  rations  per  pound  is  thus  shown  to 
have  been  the  same.  The  economic  advantage  on  the  side  of 
the  second  was  not  due  to  any  higher  nutritive  value  but 
simply  to  the  fact  that  more  of  it  was  eaten.  Similarly,  if  the 
foregoing  results  be  supposed  to  have  been  obtained,  not  with 
two  different  rations  but  with  two  different  animals  on  the 
same  kind  of  feed,  the  experiment  does  not  show  that  the  second 
animal  digested  or  assimilated  his  feed  any  more  efficiently  than 
the  first,  but  simply  demonstrates  the  economic  advantage  of 
a  larger  consumption  of  feed.  It  scarcely  need  be  added  that 
the  same  principle  applies  to  all  cases  of  productive  feeding,  as 
has  recently  been  shown  in  a  very  striking  manner  by  Eckles  l 
in  experiments  upon  dairy  cows.  Clearly,  a  knowledge  of 
the  maintenance  ration  is  essential  to  any  logical  interpretation 
of  experimental  results. 

361.  Requirements  for  maintenance.  —  Corresponding  to 
the  dual  function  of  the  feed  (263)  as  a  source  of  energy  for  the 
bodily  activities  and  of  specific  substances  necessary  for  the 
growth,  maintenance  and  repair  of  the  tissues,  the  maintenance 

1  Mo.  Exp.  Sta.,  Research  Bui.  No.  2. 


270  NUTRITION  OF  FARM  ANIMALS 

requirements  of  the  animal  and  the  values  of  feeding  stuffs  and 
rations  for  that  purpose  may  be  considered  from  two  points  of. 
view:  — 

First,  we  may  inquire  how  much  energy  is  necessary  to  sup- 
port the  quiescent  animal  and  what  amounts  of  it  the  various 
feeds  and  rations  can  supply  in  forms  available  for  this  purpose. 

Second,  we  may  ask  what  specific  materials  and  how  much 
of  each  must  be  supplied  in  the  feed  to  make  good  the  losses 
due  to  the  continual  katabolism  of  body  substances.  It  is 
particularly  the  proteins,  or  rather  the  amino  acids  composing 
them,  and  the  ash  ingredients  and  perhaps  the  so-called  vita- 
mines  which  need  to  be  considered  in  this  respect,  the  body  ap- 
parently possessing  large  powers  of  manufacturing  other  neces- 
sary ingredients  from  those  supplied  in  ordinary  feeding  stuffs. 

It  will  be  convenient  to  consider  these  two  general  classes  of 
maintenance  requirements  in  the  order  named,  the  present 
chapter  dealing  with  the  energy  requirements. 

362.  Mutual  replacement  of  organic  nutrients.  —  The  dis- 
cussion, in  Chapter  V,  of  the  functions  of  the  principal  groups 
of  organic  nutrients  (262-267)  showed  that,  besides  certain 
specific  values  as  sources  of  particular  chemical  compounds, 
they  all  serve  as  carriers  of  chemical  energy  for  the  needs  of  the 
organism.  It  would  be  anticipated,  therefore,  that  the  various 
digestible  nutrients  might  mutually  replace  each  other  or  the 
ingredients  of  the  body,  and  numerous  experiments  have  shown 
that  such  is  indeed  the  case. 

Fats  fed  to  a  previously  fasting  animal  diminish  or  suspend 
the  loss  of  body  fat,  while  carbohydrates  may  be  substituted  for 
the  feed  fat  with  a  similar  result.  As  has  already  been  shown 
(337),  body  protein  may  replace  body  fat  in  the  katabolism  of 
the  fasting  animal,  while  when  protein  is  given  to  such  an  ani- 
mal the  non-nitrogenous  portion  of  the  molecule  serves  as  a 
source  of  energy  to  the  organism  and  can  be  substituted  for  body 
fat.  On  the  other  hand,  an  excess  of  feed  protein  above  the 
minimum  requirement  can  be  replaced  by  fats  or  particularly  by 
the  carbohydrates,  and  likewise  by  organic  acids. 

In  brief,  the  animal  organism  manifests  a  remarkable  degree 
of  flexibility  as  regards  the  nature  of  the  material  which  it  can 
utilize  for  its  energy  metabolism.  Aside  from  the  small  min- 
imum of  protein  required,  the  metabolic  activities  of  the  body 


MAINTENANCE  —  THE  ENERGY  REQUIREMENTS     271 

may  be  supported,  now  at  the  expense  of  the  stored  body  fat, 
now  by  the  body  protein,  and  again  by  the  proteins,  the  fats, 
the  carbohydrates,  or  the  organic  acids,  of  the  feed.  What- 
ever may  be  true  economically,  physiologically  the  welfare  of 
the  mature  animal  is  not  conditioned  upon  any  fixed  relation 
between  the  classes  of  nutrients  in  its  feed  supply,  apart  from  the 
minimum  requirements  for  protein  and  ash.  But  while  the 
body  may  draw  its  energy  from  the  most  varied  feed  materials, 
it  by  no  means  follows  that  the  gross  energy  of  these  materials 
is  of  equal  value  for  the  functions  of  the  organism.  On  the 
contrary  it  has  been  shown  that  there  are  wide  differences  in  this 
respect. 

§  i.  NET  ENERGY  VALUES  FOR  MAINTENANCE 

363.  Method  of  determination.  —  The  value  of  any  nutrient 
or  feeding  stuff  as  a  source  of  energy  for  maintenance  is  obviously 
measured  by  the  extent  to  which  it  can  diminish  the  loss  of 
energy  which  the  body  would  otherwise  suffer.     Suppose,  for 
example,  that  a  fasting  dog  was  found  to  produce  600  Cals. 
of  heat  per  day  by  the  katabolism  of  his  own  tissues.     If,  in  a 
subsequent  experiment,  fat  be  fed,  this  loss  from  the  body  will 
be  diminished,  more  or  less  feed  fat  being  virtually  katabolized 
in  place  of  body  tissue.     If  fifty  grams  of  fat  are  fed,  and  if  a 
balance  experiment  shows  that  the  loss  of  energy  from  the 
body  is  reduced  from  600  Cals.  to  200  Cals.,  it  is  plain  that 
each  gram  of  fat  has  reduced  the  loss  by  400  -i-  50  =  8  Cals. 
and  the  latter  number  shows  the  value  of  this  particular  fat 
for  the  maintenance  of  this  particular  animal. 

364.  Comparison  with  metabolizable  energy.  —  As  already 
defined    (322),    metabolizable   energy   is   that  portion   of   the 
gross  energy  of  the  feed  which  is  not  carried  off  as  chemical 
energy  in  the  excreta  but  is  capable  of  transformation  in  the 
body.     It  was  natural  to  suppose,  therefore,  that  the  metab- 
olizable energy  of  a  substance  would  represent  its  value  for 
maintenance  and  this  was  long  believed  to.  be  true,  but  later 
investigations  have  shown  that  such  is  not  the  case. 

For  example,  in  balance  experiments  by  Armsby  and  Fries  a 
steer  received  in  successive  periods  two  different  amounts  of 
timothy  hay,  both  insufficient  for  maintenance.  The  metab- 


272 


NUTRITION  OF  FARM   ANIMALS 


olizable  energy  of  the  hay  and  the  heat  production  per  day, 
determined  in  the  manner  illustrated  in  Chapter  VI  (322,  329), 
were  as  follows  :  — 


TABLE  37.  —  DETERMINATION  OF  NET  ENERGY  VALUE  OF  TIMOTHY  HAY 


DRY  MAT- 
TER OF 
HAY  EATEN 

METABO- 

LIZABLE 

ENERGY 

HEAT  PRO- 
DUCED 

GAIN  OF 
ENERGY  l 

Period  4    

Pounds 
IO  21 

Cals. 
CK4.4. 

Cals. 
9812 

Cals. 
-  268 

Period  3     

6.17 

5768 

8064 

-2296 

Difference  
Difference  per  Ib.  dry  matter  of 
hav   • 

4.04 

3776 

QIC 

1748 

A?  -} 

2028 
CO2 

The  4.04  pounds  of  hay  (water-free),  added  to  the  insufficient 
ration  of  Period  III  diminished  the  loss  of  energy  from  the 
body  of  the  animal  by  2028  Cals. ;  that  is,  they  contributed 
this  amount  towards  its  maintenance.  The  net  effect  of  the 
hay,  therefore,  computed  exactly  as  in  the  supposed  case  of 
the  dog  in  the  preceding  paragraph,  was  2028  -f-  4.04  =  502 
Cals.  per  pound  of  dry  matter.  But  the  added  hay  contained 
metabolizable  energy  to  the  amount  of  935  Cals.  per  pound  of 
dry  matter.  Clearly,  therefore,  by  no  means  all  of  the  metab- 
olizable energy  of  the  hay  could  be  utilized  for  maintenance 
by  the  steer.  Only  502  Cals.  were  used  for  this  purpose,  in 
place  of  energy  previously  derived  from  the  katabolism  of 
the  fat  and  protein  of  the  body,  while  the  remaining  433  Cals. 
were,  indeed,  metabolized  in  the  body,  but  resulted  simply  in 
increasing  the  heat  production  by  this  amount.2  The  propor- 
tion of  the  metabolizable  energy  of  this  hay  which  was  available 
for  maintenance,  then,  was  502  -r-  935  =53.7%.  The  fore- 
going result  is  typical  of  a  large  number  of  others  which  have 
been  reached  in  experiments  on  various  species  of  animals. 

1  Since  submaintenance   rations  were  fed,  the  gains  were  of   course  negative, 
i.e.,  chemical  energy  was  lost  from  the  body. 

2  Since  gains  of  energy  are  computed  from  the  difference  between  income  and 
outgo,  the  figures  of  the  last  column  of  the  table  necessarily  agree  with  those  of  the 
two  preceding  ones.     They  simply  present  a  different  aspect  of  the  same  facts. 


MAINTENANCE  —  THE  ENERGY  REQUIREMENTS     273 

Even  in  the  case  of  pure,  or  nearly  pure,  nutrients  fed  to  carniv- 
ora,  their  maintenance  values  are  less  than  their  content  of 
metabolizable  energy. 

365.  Feed  consumption  increases  heat  production.  —  From 
a  slightly  different  point  of  view,  the  experiment  just  cited 
furnishes  a  good  illustration  of  the  important  fact  that  the 
consumption  of  feed  tends  to  increase  the  heat  production  of 
the  body.  This  is  an  observation  as  old  as  the  time  of  Lavoi- 
sier. That  investigator  observed  the  oxygen  consumption  of 
a  man  to  increase  materially  (about  37  per  cent)  after  a  meal, 
and  a  multitude  of  subsequent  experiments  by  numerous  in- 
vestigators and  on  various  species  of  animals  have  fully  con- 
firmed these  earlier  results,  so  that  the  fact  of  an  increased  metab- 
olism consequent  on  the  ingestion  of  feed  is  fully  established. 
It  is  especially  to  the  investigations  of  Zuntz  and  his  associates  l 
that  the  demonstration  of  this  fact  and  the  recognition  of  its 
significance  in  relation  to  the  nutritive  values  of  feeding  stuffs 
is  due. 

For  example,  Zuntz  and  Hageman,2  on  the  average  of  a  number  of 
experiments  in  which  the  respiratory  exchange  of  a  horse  shortly 
before  feeding  in  the  morning,  shortly  after  feeding,  and  some  hours 
later  was  determined  by  means  of  the  Zuntz  form  of  the  Pettenkofer 
apparatus  (299) ,  obtained  the  following  results,  computed  per  kilo- 
gram live  weight  per  minute. 

TABLE  38.  —  HEAT  PRODUCTION  BY  A  HORSE 


OXYGEN 
CONSUMED 

COMPUTED 
HEAT  PRO- 
DUCTION 

Fasting  ...  .  

Cubic 
Centimeters 

?.  22Q 

Gram-calories 
16.020 

23  minutes  after  feeding  
3^  hours  after  feeding  

3.648 
3-704 

18.510 

18.787 

The  same  effect  has  been  invariably  observed  with  cattle  in  experi- 
ments by  Armsby  and  Fries  3  in  which  the  heat  production  was  deter- 
mined directly  by  means  of  the  respiration  calorimeter.  Thus  in  an 

1  Compare  the  writer's  Principles  of  Animal  Nutrition,  pp.  377-385. 
2Landw.  Jahrb.,  27  (1898),  Erganzbd.  Ill,  282. 
3  Jour.  Agr.  Research,  3  (1915),  435. 


274 


NUTRITION  OF  FARM  ANIMALS 


experiment  in  which  three  different  amounts  of  alfalfa  hay  were  fed 
to  the  same  steer  in  different  periods  the  results  were  as  follows :  — 

TABLE  39.  —  HEAT  PRODUCTION  BY  A  STEER 


DRY    MATTER 
OF  FEED  PER 
DAY 

HEAT  PRO- 
DUCED PER 
DAY 

Period  i          

Kgs. 

6  638 

Cals. 

1  1  272 

Period  3 

53  20 

IO388 

Period  5 

3OC  2 

77  ^4. 

Kellner's  respiration  experiments  on  fattening  cattle  have  shown 
that  the  same  effect  is  produced  when  feed  is  added  to  a  basal  ration. 
Thus  when  wheat  gluten  was  added  to  a  light  fattening  ration  *  the 
heat  production  as  calculated  (329)  from  the  balance  of  matter  was 
as  follows : 

TABLE  40.  —  HEAT  PRODUCTION  BY  AN  Ox 


DRY    MATTER 
OF  FEED  PER 
DAY 

HEAT  PRO- 
DUCED PER 
DAY 

Kgs. 

Cals. 

Period  i, 
Period  4, 

Basal  ration       
Same  +  gluten       

10.707 
12.372 

IQ34I 
24007 

For  many  years  it  was  taught,  in  accordance  with  Rubner's  theory 
of  "isodynamic  replacement,"  that  with  carnivora,  and  presumably 
with  man,  the  nutrients  were  of  value  in  proportion  to  their  content 
of  metabolizable  energy.  Rubner's  own  later  investigations,2  how- 
ever, as  well  as  still  more  recent  ones  by  Lusk  and  his  associates 
(367  e) ,  have  shown  that  what  is  true  of  the  feeding  stuffs  consumed  by 
horses  and  cattle  is  also  true  of  nearly  pure  nutrients  fed  to  dogs,  viz., 
that  if  the  experiment  be  made  above  the  critical  temperature  for  the 
animal  there  is  in  each  case  an  increase  in  the  heat  production,  so  that 
the  metabolizable  energy  is  only  partially  available  for  maintenance. 
Thus  the  average  of  two  of  Rubner's  experiments  in  which  lean  meat 
was  fed  gave  the  following  results  as  compared  with  the  fasting  state : 

1  Landw.  Vers.  Stat.,  53  (1900),  130-131. 

2  Die  Gesetze  des  Energieverbrauchs  bei  der  Ernahrung,  1902. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     275 
TABLE  41.  —  HEAT  PRODUCTION  BY  A  DOG 


MEAT  FED 
PER  DAY 

DAILY  HEAT 
PRODUCTION 
PER  KILO- 
GRAM LIVE 
WEIGHT 

Fasting       

Grams 
o 

Cals. 
"I  i.  5o 

Fed 

274. 

70  cc 

Proteins  are  especially  efficient  in  stimulating  the  heat  production  but 
fats  and  carbohydrates  produce  the  same  effect  although  to  a  much 
less  degree. 

366.  The  specific  dynamic  action.  —  The  effect  of  the  various 
nutrients,  notably  of  protein,  in  raising  the  heat  production  of 
the  animal  above  the  fasting  level,  as  in  the  experiments  just 
cited,  has  been  called  by  Rubner  their  specific  dynamic  action. 
Kellner l  has  proposed  a  different   terminology.     He   divides 
the  metabolizable  energy  of  the  feed  into  thermic  and  dynamic 
energy.     Thermic    energy,    equivalent    to    Rubner's    specific 
dynamic   action,   signifies    that  portion  of  the   metabolizable 
energy  which  is  of  value   to  the  organism  only  as  a  source 
of  heat.     Dynamic  energy,  equivalent  to  net  energy  as  denned 
in  a  subsequent  paragraph  (370),  on  the  other  hand,  is  that 
portion  of  the  metabolizable  energy  which  can  be  utilized  for 
the  performance  of  the  vital  functions. 

367.  Causes  of  increased  heat  production.  —  The  consump- 
tion of  feed  sets  in  operation  (or  increases)  a  variety  of  activities 
not  manifested  by  the  fasting  organism. 

a.  Mechanical  Work.  —  A  not  inconsiderable  amount  of 
muscular  activity  is  expended  by  farm  animals  and  especially 
by  the  herbivora  in  the  prehension  and  mastication  of  their 
feed  and  in  moving  it  through  the  alimentary  canal.  Since 
muscular  work  involves  an  expenditure  of  energy,  all' of  which, 
in  the  case  of  internal  work,  finally  takes  the  form  of  heat  (342), 
the  mechanical  work  of  digestion  is  a  considerable  factor  in 
increasing  the  metabolism  of  farm  animals,  although  Armsby 
and  Fries2  have  presented  reasons  for  believing  that  peristalsis 

1  Ernahrung  landw.  Nutzt.,  6th  Ed.,  p.  105. 

2  Jour.  Agr.  Research,  3  (1915),  479. 


276  NUTRITION  OF   FARM   ANIMALS 

in  cattle  does  not  contribute  very  largely  to  the  increased  heat 
production  consequent  on  the  consumption  of  feed. 

b.  Glandular  activity.  —  The  increased  metabolism  required 
for  the  secretion  of  the  digestive  fluids  and  for  the  excretion  of 
metabolic  products  is  also  to  be  reckoned  among  the  causes  of 
the  heat  production  consequent  on  the  ingestion  of  feed. 

c.  Fermentations.  —  The  extensive  fermentations,  especially 
the  methane  fermentation,  occurring  in  the  digestive  tract  of 
herbivora  (128-130,  132)  result  in  a  considerable  evolution  of 
heat.     No  entirely  satisfactory  determinations  of  its  amount 
have  yet  been  reported,  but  Von  der  Heide,  Klein  and  Zuntz  1 
compute  from  MarkofTs  experiments  that  the  methane  fer- 
mentation in  cattle  gives  rise  to  the  evolution  of  4.374  Cals.  of 
heat  per  cubic  centimeter  of  methane,  equivalent  to  6.07  Cals. 
per  gram. 

d.  Intermediary  metabolism.  —  The  chemical  changes  which 
the   nutrients   undergo   during   digestion   and   resorption   and 
especially  in  the  intermediary  metabolism  (compare  Chapters 
III  and  V)  have  been  invoked  to  explain  the  increased  heat 
production  consequent  on  the  consumption  of  feed,  particularly 
of  protein,  but   apparently  without  sufficient   warrant,  most 
of  these  reactions  seeming  to  be  substantially  isothermic. 

e.  Direct  stimulus  to  metabolism.  —  Recent  investigations  by 
Lusk  and  his  associates  2  upon  the  cause  of  the  specific  dy- 
namic action,   together  with  earlier    experiments    by    Gigon,3 
have  gone  far  towards  clearing  up  the  subject.     According  to 
Lusk,  the  action  of  carbohydrates  and  fats  is  to  be  explained 
substantially  as  was  done  by  C.  Voit  in  1881,  viz.,  as  the  direct 
effect  of  a  greater  supply  of  non-nitrogenous  material  to  the 
cells,  i.e.,  as  virtually  a  case  of  mass  action.     The  products  of 
protein  katabolism,  on  the  contrary,  particularly  the  hydroxy 
and  keto-acids  resulting  from  the  deaminization  of  the  amino 
acids  (233),  act  as  direct  stimuli  to  the  katabolism  of  non- 
nitrogenous  matter  in  the  body  cells. 

That  these  actions  play  their  part,  along  with  mechanical 
work  and  fermentations,  in  bringing  about  the  increased  heat 

1  Landw.  Jahrb.,  44  (1913),  70S- 

2  Jour.  Biol.  Chem.,  12  (1912),  349;    13  (1912),  27,  155,  185;   20  (1915),  555- 
Proc. Internat.  Cong.  Hygiene,  1913.     Arch.  Inter.  Medicine,  12  (1913),  485.     Jour. 
Amer.  Med.  Asso.,  63  (1914),  824. 

3  Skand.  Arch.  Physiol.,  21  (1909),  351 ;  Arch.  Physiol.  (Pfliiger) ,  140  (1911),  548. 


MAINTENANCE  —  THE  ENERGY  REQUIREMENTS     277 

production  resulting  from  the  consumption  of  feed  by  herbivora 
cannot  be  doubted.  Besides  proteins,  carbohydrates  and  fats, 
however,  the  feed  of  herbivora  contains  a  great  variety  of  other 
substances  and  the  results  upon  steers  obtained  by  Armsby  and 
Fries  l  seem  to  indicate  that  among  these  there  may  be  com- 
pounds acting  specifically  as  stimuli  to  the  cell  metabolism  or 
to  the  minor  muscular  movements  of  the  animal.  Among  the 
feeding  stuffs  examined,  this  appeared  to  be  notably  true  of 
alfalfa  hay  and  maize  meal. 

368.  "  Work   of   digestion."  —  The    expenditure   of   energy 
by  the  body  which  results  from  the  ingestion  of  feed  has  been 
somewhat   loosely,    and   perhaps   not   altogether   fortunately, 
designated  as  "  work  of  digestion."     While  there  may  be  ob- 
jections to  the  term  and  while  it  must  not  be  interpreted  too 
literally,  it  may  nevertheless  serve  a  useful  purpose  as  a  col- 
lective expression  for  the  energy  cost  to  the  organism  of  all  the 
various  processes  involved  in  the  digestion  and  assimilation  of 
the  feed.     Its  total  amount  is  equal,  of  course,  to  the  extra 
heat  produced  above  that  generated  by  the  fasting  animal. 
Rubner's  specific, dynamic  action,  or  Kellner's  thermal  energy, 
is  equivalent  to  the  "  work  of  digestion  "  in  this  broad  mean- 
ing.    The  considerations  presented  in  the  previous  paragraphs 
serve  to  indicate  some  of  the  factors  of  the  "  work  of  digestion  " 
and  render  it  evident  that  it  is  by  no  means  all  work  in  the 
mechanical  sense.     In  herbivora  this  factor  is  an  important 
one,  while  with  man  and  carnivora  it  apparently  plays  a  small 
part.     A  similar  difference  is  strikingly  shown  in  the  case  of  the 
digestive  fermentations,  which  are  very  extensive  in  ruminants 
but  play  a  subordinate  role  in  other  animals. 

369.  Significance   of   expenditure   of   energy   in   feed   con- 
sumption. —  Whatever  the  part  played  by  various  factors  in 
the  increase  of  metabolism  due  to  feed  ingestion,  the  existence 
of  that  increase  and  the  consequent  augmented  heat  production 
is  a  fully  established  fact  which  has  an  important  bearing  upon 
the  value  of  the  feed  as  a  source  of  energy. 

Recurring  once  more  to  the  comparison  of  the  animal  body 
with  an  internal  combustion  motor  (274),  if  a  gasoline  engine 
has  to  obtain  its  supply  of  fuel  by  hoisting  it  from  a  lower 
level,  it  is  evident  that  the  energy  spent  in  this  way  diminishes 

1  Jour.  Agr.  Research,  3  (1915),  479. 


278  NUTRITION  OF  FARM  ANIMALS 

to  just  that  extent  the  quantity  of  energy  which  the  engine 
can  deliver  in  other  forms  of  work,  so  that  the  effect  is 
virtually  the  same  as  if  the  energy  content  of  the  gasoline 
as  delivered  at  the  cylinder  were  diminished  by  the  same 
amount. 

In  a  precisely  similar  way,  the  energy  expended  in  the  so-called 
"  work  of  digestion  "  and  eliminated  as  heat  does  not  serve  the 
general  purposes  of  the  body.  It  cannot  be  said  to  be  waste 
energy,  like  the  chemical  energy  of  the  feces,  for  example,  since 
part  at  least  is  expended  for  necessary  purposes.  The  feed  must 
be  eaten  and  assimilated,  just  as  the  gasoline  for  the  engine  must 
be  hoisted.  The  energy  spent  in  so  doing,  however,  consti- 
tutes virtually  a  deduction  which  must  be  made  from  the  meta- 
bolizable  energy  of  the  feed  in  order  to  obtain  the  net  amount 
of  energy  which  it  can  contribute  to  the  performance  of  the 
necessary  internal  work  of  the  body  (i.e.,  to  its  maintenance) 
or  to  such  processes  as  the  performance  of  external  work  or  the 
storage  of  meat  or  fat. 

370.  Net  energy  values.  —  By  means  of  balance  experiments 
like  that  with  a  steer  used  as  an  illustration  in  a  previous  para- 
graph (364),  the  effect  of  a  feeding  stuff  upon  the  heat  produc- 
tion of  an  animal  or  the  amount  of  energy  which  it  contributes 
towards  the  maintenance  of  the  body  may  be  determined. 
The  latter  result  has  been  called  the  net  energy  "value  of  the  sub- 
stance because  it  shows  the  net  result  as  regards  energy  obtained 
by  its  use.-  The  net  energy  value  of  the  hay  in  the  illustration 
cited  was  502  Cals.  per  pound  of  dry  matter.  Net  energy  might 
be  denned,  therefore,  as  metabolizable  energy  minus  the  work  of 
digestion,  the  latter  term,  of  course,  being  understood  in  the 
very  general  sense  already  indicated  as  equivalent  to  the 
additional  heat  production  caused  by  the  consumption  of 
the  feed. 

Stated  in  a  slightly  different  way,  the  net  energy  value  of  a 
feeding  stuff  is  the  energy  remaining  after  the  losses  of  chemical 
energy  in  the  various  excreta  and  also  the  energy  expended  in 
the  processes  incident  to  the  consumption  of  the  material 
have  been  deducted  from  its  gross  energy.  The  amount  of  these 
deductions  naturally  varies  as  between  different  feeding  stuffs. 
One  containing  much  digestible  matter,  readily  masticated  and 
exerting  little  stimulating  effect  on  the  metabolic  processes 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     279 

(367  e),  that  is,  causing  little  "  work  of  digestion,"  will  have  a 
relatively  high  net  energy  value;  while,  on  the  other  hand, 
materials  of  low  digestibility,  which  undergo  extensive  fer- 
mentations, require  much  muscular  work  in  their  mastication 
and  digestion,  or  stimulate  the  body  metabolism,  will  have 
correspondingly  low  net  energy  values. 

371.  Net  energy  values  for  different  purposes.  —  The  net 
energy  value  of  the  same  feeding  stuff  may  differ  according  to 
the  species  of  animal  by  which  it  is  consumed  and  the  purpose 
for  which  it  is  used. 

The  structure  of  the  digestive  organs  of  different  species  varies 
and,  as  is  shown  in  Chapter  XVI  (713-717),  specific  differences 
in  digestive  capacity  exist.  In  other  words,  the  proportion  of 
the  gross  energy  of  a  feeding  stuff  which  is  lost  in  the  feces 
differs  as  between  different  species,  and  therefore  its  net  energy 
value  tends  to  vary  accordingly.  Similarly,  the  extent  to  which 
bacterial  fermentations  occur  in  the  digestive  tract  of  an  animal 
tends  to  influence  the  net  energy  value  of  its  feed  in  two  ways. 
The  more  extensive  these  fermentations,  the  less  of  the  chemical 
energy  of  the  feed  is  rejected  in  the  feces  but,  on  the  other  hand, 
the  more  chemical  energy  is  given  off  in  the  combustible  gases 
excreted  or  is  transformed  into  heat  in  the  process  of  fermenta- 
tion and  increases  the  "work  of  digestion."  Finally,  it  appears 
not  unlikely  that  the  mechanical  work  required  in  mastication 
and  digestion  may  vary  as  between  different  species. 

The  materials  resorbed  from  maintenance  or  submaintenance 
rations  may  be  regarded  chiefly  as  fuel  to  be  oxidized  more  or 
less  directly,  while  in  the  fattening  or  growing  animal  a  part  of 
the  digested  nutrients  is  transformed  into  flesh  or  fat,  or  in 
the  milking  animal  into  butter  fat,  lactose,  casein,  etc.  The 
net  energy  values  for  these  purposes  would  evidently  be  equal 
to  the  amounts  of  energy  contained  in  the  gains  made  and 
might  very  well  differ  from  the  values  for  simple  maintenance. 

The  net  energy  values  of  feeding  stuffs  for  different  species 
and  for  the  various  purposes  for  which  farm  animals  are  kept, 
together  with  the  methods  for  their  determination  or  estimation, 
are  discussed  in  Chapter  XVII  and  the  average  results  for  a 
considerable  number  of  feeding  stuffs  are  tabulated  in  the  Ap- 
pendix. What  is  essential  at  this  point  is  to  acquire  a  clear 
idea  of  the  general  conception. 


280  NUTRITION  OF  FARM  ANIMALS 

§  2.  THE  MAINTENANCE  REQUIREMENTS  OF  FARM  ANIMALS 

372.   True   maintenance   and   live   weight   maintenance.  - 

The  maintenance  of  an  animal  in  the  strict  sense  signifies  the 
preservation  of  the  store  of  matter  and  of  potential  energy 
contained  in  the  body,  and  only  a  ration  which  effects  this  is 
really  a  maintenance  ration.  As  will  appear  in  subsequent 
pages,  however,  much  of  the  recorded  information  regarding 
the  maintenance  ration  is  derived  from  experiments  in  which 
the  criterion  of  the  sufficiency  of  the  ration  was  its  effect  in 
maintaining  the  live  weight  of  the  animal.  In  experiments  on 
mature  animals  and  extending  over  a  considerable  period  of 
time,  it  is  unlikely  that  any  gross  error  is  involved,  especially 
if  determinations  of  the  nitrogen  balance  show  the  protein 
supply  to  be  adequate.  In  short  periods,  on  the  other  hand, 
and  especially  in  experiments  on  young  animals,  the  live  weight 
is  a  notoriously  untrustworthy  guide.  The  general  reasons 
for  this  are  familiar,  but  in  young  animals  another  very  impor- 
tant factor  enters  into  consideration.  As  is  well  known,  the 
tendency  to  growth  is  one  of  the  most  marked  characteristics 
of  young  animals.  Waters  l  has  shown  that  this  impulse  to 
increase  of  tissue  is  so  marked  that  it  may  apparently  take  pre- 
cedence over  the  demand  for  maintenance,  and  that  an  animal 
may  even  maintain  its  weight  and  continue  to  increase  in  size 
of  skeleton  for  a  considerable  time  on  a  sub-maintenance  ration. 

Some  15  immature  cattle  were  fed  for  considerable  periods  on 
rations  just  sufficient  to  maintain  their  live  weight.  Under  these 
conditions,  the  animals  continued  to  grow  in  height,  in  depth  of  chest 
and  length  of  head.  At  the  same  time,  however,  there  was  an  evi- 
dent falling  off  in  the  amount  of  fat  tissue,  both  as  judged  by  the  eye 
and  as  shown  by  the  appearance  and  by  the  chemical  composition  of 
the  carcass.  Histological  studies,  too,  showed  a  reduction  in  the  size 
of  the  fat  cells  and  analyses  of  the  adipose  tissue  showed  a  lower  fat 
and  higher  water  and  protein  content  than  in  check  animals.  What 
occurred  was  evidently  a  consumption  of  body  fat  to  supply  energy, 
while  at  the  same  time  an  approximately  equal  weight  of  protein 
tissue  was  produced,  which,  on  account  of  the  relatively  low  energy 
value  of  protein  and  of  the  relatively  large  amount  of  water  accom- 
panying it,  represented  a  much  smaller  quantity  of  energy  than  did 
the  fat  tissue  which  disappeared.  In  other  words  the  rations  were 
1  Soc.  Prom.  Agr.  Sci.,  Proc.  2gth  Annual  Meeting  (1908),  p.  71. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     281 


not  really  but  only  apparently  maintenance  rations.  It  is  perhaps 
hardly  correct  to  say  that  in  these  experiments  growth  was  main- 
tained at  the  expense  of  the  fat  of  the  tissues.  A  more  exact  state- 
ment of  the  case  would  be  that  the  increase  of  protein  tissue  and 
water  masked  the  loss  of  fat.  Presumably  this  effect  would  be  less 
marked  in  more  mature  animals,  in  which  the  true  maintenance  and 
the  live  weight  maintenance  would  doubtless  approach  each  other 
closely  when  measured  over  long  periods. 

373.  Methods  of  determining  the  maintenance  requirement. 

—  The  most  obvious  method  for  determining  the  maintenance 
requirement  of  an  animal  is  the  method  of  trial.  It  consists  of 
varying  the  amount  of  feed  until  constancy  of  live  weight  is 
attained  or  until  a  balance  experiment  shows  equilibrium  be- 
tween income  and  outgo  of  matter  and  energy.  This  method, 
if  extended  over  a  considerable  length  of  time,  is  particularly 
adapted  to  the  determination  of  the  live  weight  maintenance. 
When  tested  by  the  more  refined  method  of  the  balance  ex- 
periment, however,  such  a  ration  will  only  rarely  and  by  acci- 
dent be  found  to  be  exactly  a  true  maintenance  ration.  Usu- 
ally there  will  be  revealed  more  or  less  gain  or  loss  by  the  body 
for  which  a  correction  must  be  applied. 

A  second  method  consists  of  a  comparison,  like  that  used  in 
a  previous  paragraph  (364),  to  illustrate  the  determination  of 
net  energy  values,  between  the  effects  of  two  different  amounts 
of  the  same  feeding  stuff  or  ration  upon  the  balance  of  energy. 
Such  a  comparison  not  only  affords  the  means  of  computing 
the  net  energy  value  of  the  feed  consumed  but  also  serves  to 
determine  the  energy  requirement  of  the  animal.  The  results 
in  the  case  cited  were  as  follows :  — 

TABLE  42.  —  DETERMINATION  or  MAINTENANCE  REQUIREMENT 


DRY 

MATTER 
OF  HAY 

EATEN 

METAB- 
OLIZABLE 
ENERGY 

HEAT 
PRO- 
DUCED 

GAIN  OF 
ENERGY 

Pounds  » 
IO.2I 

Cals. 
9:544 

Cals. 
9812 

Cals. 
-268 

Periods      

6.17 

5768 

8064 

-2296 

Difference        

4.O4 

^776 

1748 

2028- 

Difference  per  Ib.  of  dry  matter  of  hay 

935 

433 

502 

282  NUTRITION  OF  FARM  ANIMALS 

Each  pound  of  dry  matter  of  the  hay  decreased  the  loss  of  energy 
from  the  body  by  502  Cals.  The  ration  of  10.21  Ib.  still 
permitted  a  loss  from  the  animal  of  268  Cals.  To  reduce  this 
loss  to  zero  would  obviously  require  the  addition  of  268  -—  502 
=  0.53  Ib.  and  an  exact  maintenance  ration  as  regards  energy 
would  have  been  10.21  +  0.53  =  10.74  pounds  of  the  hay. 
In  precisely  similar  fashion  the  metabolizable  energy  required 
for  maintenance  was 

9544  +  268  X  fjjf  =  10042  Cal. 

374.  Computation  of  the  fasting  katabolism.  —  Another 
method  of  comparison,  however,  is  of  greater  significance,  since  it 
affords  results  of  more  general,  value  and  also  serves  to  bring  out 
clearly  the  relations  between  the  net  energy  values  of  feeding 
stuffs,  the  fasting  katabolism  and  the  maintenance  requirement. 

In  the  foregoing  experiments  each  pound  of  hay  withdrawn 
from  the  ration  caused  the  heat  production  to  decrease  by 
433  Cals.  If,  then,  all  the  hay  were  withdrawn  from  Period  3 
and  the  animal  reduced  to  the  fasting  state,  the  heat  production, 
or  in  other  words  the  fasting  katabolism,  would  be 

8064  -  (433  X  6.17)  =  5392  Cals. 

The  same  result  may  also  be  computed  from  the  losses  of 
energy  suffered  by  the  animal.  The  withdrawal  of  each  pound 
of  hay  increased  this  loss  by  502  Cals.  The  withdrawal 
of  all  the  6.17  pounds  of  Period  3,  therefore,  would  increase 
the  loss  by  502  X  6.17  =  3096  Cals.,  making  a  total  loss 
of  5392  Cals.,  equal  to  the  fasting  katabolism.  In  other 
words,  by  such  a  comparison  as  the  foregoing  it  is  possible  to 
determine  indirectly  the  fasting  katabolism,  which  it  is  scarcely 
practicable  to  determine  directly. 

It  was  shown  in  Chapter  VII  (344),  however,  that  the  fast- 
ing katabolism  is  the  measure  of  the  maintenance  requirement. 
To  maintain  the  steer  of  this  illustration  it  would  be  necessary 
to  supply  in  his  feed  an  amount  of  energy,  after  deducting  the 
losses  in  the  excreta  (i.e.,  an  amount  of  metabolizable  energy), 
equal  to  the  fasting  katabolism,  5372  Cals.,  plus  a  sufficient 
additional  amount  to  offset  the  additional  heat  production 
which  the  consumption  of  the  feed  would  inevitably  occasion, 
i.e.,  the  work  of  digestion. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     283 

But  the  difference  between  the  metabolizable  energy  and 
the  work  of  digestion  is  the  net  energy  (370).  Consequently 
the  foregoing  statement  is  equivalent  to  saying  that  the  main- 
tenance requirement  of  the  steer  was  5392  Cals.  of  net  energy. 
Each  pound  of  this  particular  hay  had  a  net  energy  value  of 
502  Cals.  To  maintain  the  animal,  therefore,  there  would  be 
required  5392  -s-  502  =  10.74  lb.,  as  previously  computed. 

375.  Manner  of  stating  the  maintenance  requirement.  — 
Evidently  the  maintenance  requirement  of  an  animal,  such  as 
the  steer  of  the  foregoing  illustration,  may  be  stated  in  a  va- 
riety of  ways  —  in  terms  of  weight  of  feed,  of  amounts  of  di- 
gestible nutrients,  of  metabolizable  energy  or  of  net  energy. 
So  far  as  the  results  of  a  single  experiment  are  concerned,  it 
makes  little  difference  which  manner  of  statement  is  adopted, 
since  they  are  all  simply  different  ways  of  expressing  the  same 
facts.  When  it  is  desired  to  make  general  statements,  however, 
there  are  very  manifest  advantages  in  stating  the  maintenance 
ration  in  terms  of  net  energy. 

It  was  shown  in  Chapter  VII  (343)  that  the  fasting  katabo- 
lism  might  be  regarded  as  practically  constant  under  uniform 
conditions.  Consequently  the  net  energy  requirement  for 
maintenance  is  equally  constant,  and  in  the  foregoing  example 
any  ration  having  a  net  energy  value  of  5392  Cals.  would 
have  been  a  maintenance  ration. 

But  since  the  net  energy  values  of  different  feeding  stuffs, 
as  well  as  the  proportion  of  their  metabolizable  energy  which 
can  be  utilized  for  maintenance,  may  vary  through  a  consider- 
able range,  the  weight  of  feed  or  the  amount  of  metabolizable 
energy  which  will  suffice  to  maintain  an  animal  will  vary  with 
the  kind  of  material  fed.  For  example,  it  is  shown  in  subsequent 
paragraphs  (380,  381)  that  a  thousand-pound  steer  requires 
about  6.0  Therms  of  net  energy  for  maintenance.  From  the 
results  of  Armsby  and  Fries'  determinations  of  net  energy  values 
(760),  it  is  easy  to  compute  that  to  supply  this  amount  in  tim- 
othy hay  with  a  net  energy  value  of  48.63  Therms  per  100 
pounds  of  dry  matter  would  require  6.0  -4-  0.4863  =  12.34 
pounds  of  dry  matter,  but  that  if  mixed  hay  with  a  net  energy 
value  of  43.37  Therms  per  1000  pounds  were  used,  the  amount  of 
dry  mattes  necessary  would  be  6.0  -f-  0.4337  =  J3-83  pounds. 
The  quantities  of  metabolizable  energy  contained  in  these  main- 


284 


NUTRITION  OF   FARM   ANIMALS 


tenance  rations  would  likewise  be  different,  as  is  shown  in  the 
following  statement,  in  which  are  included  for  further  illustra- 
tion two  mixed  rations  used  by  the  same  experimenters. 

TABLE  43.  —  EXAMPLES  or  MAINTENANCE  RATIONS  FOR  A  IOOO-POUND 

STEER 


MATERIAL 

WEIGHT 
OF  DRY 
MATTER 

METAB- 
OLIZABLE 
ENERGY 

NET 
ENERGY 

Timothy  hay 

Pounds 

12.34 

13-83 
8.68 
9.07 

Therms 
10.38 
12.01 
II.  II 
I0.6g 

Therms 
6.0 
6.0 
6.0 
6.0 

jVtixed  hay  . 

Corn  meal  and 
Mixed  grain  an 

mixed  hay   2  *  i 

d  alfalfa  hay,  2:1    

By  stating  the  maintenance  requirement  in  terms  of  net  energy 
a  single  value  is  obtained  for  an  animal,  or  a  single  average  for 
a  class  of  animals,  which  is  a  general  expression  of  its  main- 
tenance requirement  irrespective  (substantially)  of  the  par- 
ticular feed  or  feeds  which  may  be  used  to  satisfy  it,  while  a 
statement  in  terms  of  metabolizable  energy  or  of  weight  of 
feed  must  also  specify  the  particular  kind  of  feed  to  which  it 
applies.  The  greater  convenience  of  the  former  method  for 
the  computation  of  actual  rations  is  evident.  To  the  extent  to 
which  the  net  energy  values  of  feeding  stuffs  are  known  or  can 
be  estimated  it  is  possible  to  make  up  an  almost  endless  variety 
of  combinations  which  will  all  be  maintenance  rations,  i.e., 
will  furnish  the  amount  of  net  energy  required  by  the  animal. 

In  the  following  paragraphs,  this  method  of  expression  will  be 
followed  so  far  as  practicable,  although  unfortunately  compara- 
tively few  determinations  of  the  net  energy  requirements  for 
maintenance  have  yet  been  reported  except  in  the  case  of  cattle. 

376.  Modified  conception  of  energy  requirement. —  A  study 
of  the  conditions,  especially  as  regards  muscular  work,  which 
influence  the  katabolism  of  the  fasting  animal  makes  it  evident 
that  the  conception  of  the  energy  requirement  outlined  in 
Chapter  VII  requires  some  modification  in  its  application  to 
the  actual  feeding  of  animals. 

As  was  there  shown  (344),  the  heat  production  of  the  fasting 
animal  in  a  state  of  absolute  muscular  rest  may  be  regarded  as 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     285 

measuring  the  quantity  of  energy  indispensable  for  its  internal 
work.  As  a  matter  of  fact,  however,  absolute  muscular  rest 
cannot  be  maintained  for  any  considerable  length  of  time,  at 
least  during  the  waking  hours,  even  by  voluntary  effort.  The 
horse  or  ox  when  at  rest  in  the  ordinary  sense,  i.e.,  when  doing 
no  external  work,  is  still  expending  a  not  inconsiderable  amount 
of  energy  in  muscular  activities  of  various  sorts,  some  of  which 
were  indicated  in  §3  of  the  same  chapter  (348).  In  particular, 
it  was  stated  (349)  that  standing  as  compared  with  lying  causes 
a  very  marked  increase  in  the  heat  production,  especially  in 
the  case  of  cattle.  When,  therefore,  the  heat  production  of 
such  an  animal  in  the  fasting  state  is  taken  as  a  measure  of  the 
energy  required  for  its  maintenance,  it  does  not  represent  a 
state  of  absolute  rest  but  simply  with  one  of  relatively  less 
activity.  The  energy  requirement  for  maintenance  in  the 
economic  sense  includes  not  only  the  absolute  minimum  re- 
quired for  the  internal  work  but  also  the  amount  expended  in 
various  forms  of  incidental  muscular  work  which  are  in  a  sense 
unnecessary  physiologically  but  are  unavoidable  practically. 
Moreover,  since  the  amount  of  this  incidental  work  is  more  or 
less  variable  as  between  different  individuals  and  in  the  same 
individual  at  different  times,  the  energy  requirement  for  main- 
tenance is  not  a  fixed,  constant  quantity  whose  exact  value  can 
be  determined,  but  a  variable  one.  The  purpose  of  investiga- 
tion is  to  show  the  range  of  variation  which  may  be  expected 
and  to  determine  a  general  average  value  for  the  conditions  of 
ordinary  practice. 

The  maintenance  requirement  of  swine 

377.  Net  energy  requirement.  —  With  animals  such  as  man, 
carnivora  or  swine,  having  a  comparatively  simple  digestive 
apparatus  and  consuming  relatively  concentrated  feed,  the 
fasting  energy  expenditure  can  be  determined  without  special 
difficulty  by  depriving  the  resting  animal  of  feed  during  a  rela- 
tively short  period  and  measuring  the  katabolism  with  the 
aid  of  a  respiration  apparatus  or  calorimeter.  The  total 
amount  of  heat  produced,  determined  either  directly  or 
by  calculation,  furnishes  the  measure  of  the  energy  expenditure 
and  therefore  of  the  net  energy  requirement  for  maintenance. 


286 


NUTRITION  OF  FARM  ANIMALS 


Such  an  experiment  must,  of  course,  be  made  at  a  temperature 
above  the  critical  temperature  (354)  for  the  animal,  since  other- 
wise the  heat  produced  would  be  greater  than  that  correspond- 
ing to  the  necessary  internal  work  by  the  additional  amount 
necessary  to  maintain  the  body  temperature. 

Numerous  determinations  of  the  fasting  katabolism  of  man 
and  of  the  smaller  animals,  such  as  the  dog,  cat,  rabbit,  guinea 
pig,  etc.,  are  on  record,  but  the  only  experiments  of  this  sort 
upon  farm  animals  are  those  of  Meissl,  Strohmer  and  Lorenz  1 
and  of  Tangl 2  upon  swine. 

Meissl's  determinations  were  made  at  about  20°  C.,  a  tem- 
perature which,  according  to  TangPs  later  results,  is  well  above 
the  critical  temperature  for  mature  swine.  In  Tangl's  experi- 
ments the  animals  spent  most  of  the  time  lying;  in  Meissl's 
paper  no  statements  are  made  on  this  point. 

Excluding  those  of  Tangl's  experiments  which  were  appar- 
ently below  the  critical  temperature,  the  results,  computed 
per  100  pounds  in  proportion  to  the  two-thirds  power  of  the 
live  weight,  were  as  follows :  — 

TABLE  44.  —  NET  ENERGY  FOR  MAINTENANCE  OF  SWINE 


LIVE  WEIGHT 

NET  ENERGY 
PER  100  POUNDS 
LIVE   WEIGHT 
PER  DAY 

MeissVs  experiments. 
Swine  H  l  

Lb. 

308 

Therms 
I  283 

Swine  H2 

2C/1 

I   244. 

Average 

I  266 

Tangl's  experiments. 
Two  mature  animals 
at  i6°-i7°  C.  .               

266 

I  2  2O 

at  22°  C  

266 

1.224, 

Two  growing  animals 
at  20°  C  

106 

I.3O7 

at  23°  C 

IO7 

I  226 

at  26°  C  

lie 

1.  2  7O 

Average  

I  240 

i  Ztschr.  Biol.,  22  (1886),  63. 


2  Biochem.  Ztschr.,  44  (1912),  252. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     287 

From  the  foregoing  results  it  appears  that  the  average  daily 
energy  expenditure  of  fasting  swine  at  rest  and  above  the  critical 
temperature  is  about  1.25  Therms  per  100  pounds  live  weight, 
and  consequently  that  a  maintenance  ration  must  supply  this 
amount  of  net  energy.  Assuming  a  value  of  9.02  for  the  con- 
stant k  of  Meeh's  formula  (346),  this  average  is  equivalent  to 
1.089  Therms  per  square  meter  of  body  surface.  Using  an 
entirely  different  experimental  method,  Fingerling,  Kohler  and 
Reinhardt l  have  computed  the  average  energy  requirement 
for  maintenance  of  two  growing  pigs  at  almost  the  same 
amount,  viz.,  1.045  Therms  per  square  meter. 

378.  Metabolizable  energy  in  maintenance  rations.  Un- 
fortunately, few  determinations  of  the  net  energy  values  of 
feeding  stuffs  for  swine  have  been  reported  (761)  and  most  of 
the  data  regarding  the  maintenance  requirement  of  this  species 
are  expressed  in  terms  of  digestible  matter  or  of  computed 
metabolizable  energy.  The  metabolizable  energy  contained 
in  actual  maintenance  rations  of  swine  has  been  determined  in 
a  single  respiration  experiment  by  Von  der  Heide  and  Klein  2 
and  may  be  estimated  more  or  less  accurately  in  a  number  of 
live  weight  experiments.  Such  experiments  have  been  re- 
ported by  Taylor,3  Carlyle,4  Ostertag  and  Zuntz  5  and  Dietrich.6 
The  results  show  a  very  wide  range,  from  a  minimum  of  0.897 
Therm  per  100  pounds  live  weight  for  5o-pound  pigs  on  a 
ration  of  one  part  meal  and  4  parts  skim  milk  to  a  maximum 
of  2.558  Therms  for  loo-pound  pigs  on  a  ration  of  shorts, 
corn  meal  and  oil  meal.  For  this  there  may  be  a  variety  of 
reasons.  Live  weight  results  are  notoriously  uncertain  (281- 
283),  and  in  growing  animals  especially  the  possibility  of  a  main- 
tenance of  live  weight  by  a  substitution  of  water  for  fat  (372) 
has  to  be  borne  in  mind.  The  feeds  used,  too,  were  varied, 
and  there  seem  to  be  indications  that,  in  some  cases  at  least, 
a  smaller  "  work  of  digestion,"  especially  in  the  case  of  rations 
containing  much  milk,  may  have  contributed  to  reduce  the 
amount  of  metabolizable  energy  necessary  for  maintenance. 

The  averages  computed  from  all  the  experiments  and  those  ob- 
tained by  the  omission  of  a  few  extreme  results  are  as  follows :  — 

1  Landw.  Vers.  Stat.,  84  (1914),  149.  2  Biochem.  Ztschr.,  55  (1913),  195. 

3  Wis.  Expt.  Sta.,  Rpt.  1901,  p.  67.  * Ibid.,  Bui.  104  (1903),  P-  3i- 

5  Landw.  Jahrb.,  37  (1908),  226.  6  Ills.  Expt.  Sta.,  Bui.  163  (1913). 


288  NUTRITION  OF  FARM  ANIMALS 

TABLE  45.  —  DAILY  MAINTENANCE  RATIONS  OF  SWINE 
Metabolizable  energy  per  100  Ib.  live  weight 

Maximum 2.558  Therms 

Minimum 0.897  Therm 

Average  of  all 1-534  Therms 

Average  omitting  lowest  and  highest      .     .     .  1.510  Therms 

Average  omitting  lowest  and  two  highest   .     .  1.474  Therms 

379.  Comparison  with  net  energy.  —  On  the  average  of  all 
the  respiration  experiments  on  fattening  swine  which  are  re- 
corded in  Chapter  XVII  (761),  78.14  per  cent  of  the  metab- 
olizable  energy  supplied  may  be  computed  to  have  been  uti- 
lized for  maintenance  plus  gain.     If  this  may  be  assumed  to 
represent  approximately  the  percentage  of  the  metabolizable 
energy  available  for  maintenance,  the  foregoing  maintenance 
rations  contained,  per  100  pounds  live  weight,  the  following 
amounts  of  net  energy:  — 

TABLE  46.  —  DAILY  MAINTENANCE  RATIONS  OF  SWINE 
Computed  net  energy  per  100  Ib.  live  weight 

Minimum 0.701  Therm 

Maximum 1.998  Therms 

Average  of  all i-JQQ  Therms 

The  averarge  requirement  of  net  energy  as  thus  computed 
does  not  differ  greatly  from  the  amount  indicated  by  the  ex- 
periments on  fasting  animals  (377),  but  the  enormous  range  in 
the  results  of  the  single  experiments  shows  in  a  striking  manner 
the  need  for  further  investigation. 

The  maintenance  requirement  of  cattle 

380.  Net  energy  requirement.  —  In  the  case  of  ruminants, 
it  is  hardly  practicable  to  determine  directly  the  net   energy  re- 
quirement by  measuring  the  katabolism  of  the  fasting  animal. 
Prolonged  fasting  would  be  required  to  free  the  voluminous 
and  complicated  digestive  organs  of  these  animals  from  feed 
residues,  if  this  could  be  accomplished  at  all,  and  it  would  be 
difficult  to  determine  when  that  point  was  reached,  while  it  is 
questionable  whether  the  results  on  such  an  animal  could  be 
regarded  as  normal. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     289 


TABLE  47.  —  NET  ENERGY  REQUIREMENT  FOR  MAINTENANCE  OF  CATTLE 
Corrected  to  1 2  hours  standing 


YEAR 


ANIMAL 


KIND  OF  FEED 


NET 
ENERGY 
PER   DAY 

AND     IOOO 

LB.    LIVE 
WEIGHT 


1902 I 

1903 

1904 

1905 A 

1905 B 

1906 A 

1906 B 

1907 A 

D 
E 
E 

1908 <; 

C  (Fat) 
C  (Fat) 

F 

1909 

D 

I) 

D 

1911 

G 

G 

1912 i    1 

Average  of  all 

Average,  omitting  alfalfa  meal  . 
Average  of  expts.  with  roughage 

only l 

Average  of  expts.  with  mixed 

rations    . 


Timothy  hay  and  a 

little  linseed  meal 
Clover  hay 
Clover  hay 
Timothy  hay 
Timothy  hay 
Timothy  hay 
Timothy  hay 
Timothy  hay 
Timothy  hay 
Alfalfa  hay 
Alfalfa  hay 
Alfalfa     hay     and 

grain  mixture 
Alfalfa  hay 
Alfalfa     hay     and 

grain  mixture 
Alfalfa  hay 
Alfalfa     hay     and 

grain  mixture 
Maize  stover 
Mixed   clover   and 

timothy  hay 
Mixed     hay     and 

hominy  feed 
Mixed   clover   and 

timothy  hay 
Mixed     hay     and 

maize  meal 
Alfalfa  hay 
Alfalfa  meal 


Therms 

7-430 
5.877 
7.109 

S.873 
6.052 
6.272 
6.305 
4.723 
6.067 
4.917 
4.824 

6.295 
5.246 

6.099 
5.448 

6.474 
5.858 

6.644 
5.960 

6-559 

6.141 
5.7io 
3.976 


5.906 
5.995 

5.936 
6.194 


1  Omitting  experiment  on  alfalfa  meal. 


2  go  NUTRITION  OF   FARM  ANIMALS 

The  fasting  katabolism  of  such  an  animal  may,  however, 
be  computed  in  the  manner  already  described  (374)  from  a 
comparison  of  two  periods  on  different  amounts  of  the  same 
feed,  or  ration,  both  being  less  than  that  necessary  for  main- 
tenance. Twenty-three  experiments  of  this  sort,  on  nine 
different  steers,  only  one  of  which  was  fat,  in  which  the  rela- 
tive metabolism  of  the  animals  when  standing  and  when  lying 
was  determined,  have  been  made  by  Armsby  and  Fries.1  Com- 
puted per  1000  lb.,  in  proportion  to  the  two-thirds  power  of 
the  live  weight  (347)  and  corrected 2  to  a  uniform  period  of  1 2 
hours  standing  out  of  the  24,  the  net  energy  requirements  were 
as  shown  in  Table  47.  No  other  experiments  on  precisely  this 
plan  have  yet  been  reported. 

Even  if  a  few  seemingly  extreme  results,  like  those  of  1902 
and  1912  be  excluded,  the  figures  show  a  wide  range.  The 
trials  with  mixed  rations  of  roughage  and  concentrates  show 
on  the  whole  somewhat  higher  results  than  those  with  rough- 
age only,  but  the  experiments  are  hardly  numerous  enough  to 
show  whether  this  difference  is  significant. 

381.  Net  energy  in  maintenance  rations.  —  A  considerable 
number  of  earlier  experiments  are  also  on  record  in  which  the 
amounts  of  net  energy  contained  in  actual  maintenance  rations 
of  cattle  may  be  computed  with  more  or  less  accuracy. 

The  early  experiments  of  Henneberg  and  Stohmann,  on  which 
was  based  Wolff's  feeding  standard  for  maintenance  long  cur- 
rent, as  well  as  a  considerable  number  of  subsequent  ones,3 
have  now  chiefly  an  historic  interest.  Of  the  later  investiga- 
tions, by  far  the  most  important  are  those  by  G.  Kiihn  and  by 
Kellner 4  in  which  approximate  maintenance  rations  were  fed. 
The  small  gains  or  losses  of  protein  and  fat  by  the  animals  were 
determined  by  means  of  a  Pettenkofer  respiration  apparatus 
and  corrected  for  upon  the  basis  of  results  obtained  in  other 
respiration  experiments  on  productive  rations,  and  in  this  way 
the  metabolizable  energy  required  for  maintenance  was  com- 
puted. 

1  Eight  of  them  have  been  reported.     U.  S.  Dept.  Agr.,  Bur.  Anira.  Indus., 
Buls.  74,  101,  and  128. 

2  In  the  manner  described  in  Jour.  Agr.  Research,  3  (1915),  454. 

3  Compare  Penna.  Expt.  Sta.,  Bui.  42  (1898)',  pp.  8-21. 

4  Reported  by  Kellner :  Landw.  Vers.  Sta.,  53  (1900),  pp.  6-16. 


MAINTENANCE  —  THE  ENERGY  REQUIREMENTS     2  91 


In  addition  to  these  respiration  experiments,  investigations 
upon  the  live  weight  maintenance  of  cattle  made  by  the  writer,1 
by  Haecker,2  and  by  Evvard  3  have  been  discussed  elsewhere  4 
by  the  writer. 

TABLE  48.  —  NET  ENERGY  IN  DAILY  MAINTENANCE  RATIONS  OF  CATTLE 


No.  OF  SINGLE 
EXPERIMENTS 

CHARACTER  OF 
FEED 

CONDITION 
OF  ANIMALS 

PER   1000  POUNDS 
LIVE  WEIGHT 

Maximum 
Therms 

Minimum 
Therms 

be  S 

03  5 

«5n 

Respiration 

experiments 

17 

Armsby  and  Fries  . 

Roughage  5 

Medium 

7.430 

4.723 

5-936 

5 

Armsby  and  Fries  . 

Mixed  rations  5 

Medium 

6.474 

5.960 

6.194 

22 

Armsby  and  Fries  . 

Average  of  all  5 

Medium 

7.430 

4.723 

5.995 

7 

Kellner     .... 

Roughage 

Medium 

6.780 

4.921 

5.742 

29 

Average  6    .     .     . 

5-934 

Kellner     .... 

Mixed  rations 

Fat 

8.871 

7.319 

7.946 

Live  weight 

experiments 

10 

Armsby    .... 

(Hay  only) 

Thin 

7-044 

6.136 

6.505 

3 

Armsby    .... 

(Mixed  rations) 

Thin 

6.039 

4.713 

5-423 

6 

Haecker   .... 

Medium 

5.676 

4.662 

5.021 

3 

Evvard,  ist  6o-day 

expt  

Mixed  rations 

Medium 

7.850 

6.450 

7.180 

i 

Evvard,     362-day 

expt  

Mixed  rations 

Medium 

—  . 

— 

8.090 

7 

Eckles      .... 

Mixed  rations 

Medium 

7.079 

5.841 

6.173 

Average  6    .     .     . 

6.181 

3 

Evvard,  2d  6o-day 

Mixed  rations 

Partly 

experiment 

fattened 

10.620 

8.150 

9.070 

For  the  purpose  of  computing  the  approximate  net  energy 
values  of  these  rations  it  seems  permissible  to  assume  provi- 
sionally that  the  same  proportion  of  their  metabolizable  energy 

1  Penna.  Expt.  Sta.,  Bui.  42  (1898).  2  Minn.  Expt.  Sta.,  Bui.  79- 

3  Thesis  for  degree  of  M.  S.,  University  of  Missouri,  1909. 

4  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  143,  44-46. 
6  Omitting  the  experiment  on  alfalfa  meal. 

6  Giving  each  experiment  equal  weight. 


292  NUTRITION  OF  FARM  ANIMALS 

was  available  for  maintenance  as  in  the  case  of  the  hays  exclu- 
sive of  alfalfa  investigated  by  Armsby  and  Fries,1  viz.,  52.8  per 
cent.  For  the  mixed  rations  a  percentage  of  55  has  been  as- 
sumed. In  Evvard's  experiments  the  net  energy  was  computed 
by  that  investigator.  Eckles  2  has  also  reported  five  determi- 
nations of  the  live  weight  maintenance  of  dry  cows  in  which 
the  net  energy  values  of  the  mixed  rations  consumed  were 
estimated  from  the  writer's  computed  averages.3 

The  results  of  the  computations  are  shown  in  Table  48, 
Armsby  and  Fries'  determinations  of  the  net  energy  require- 
ment being  included  for  comparison. 

For  the  medium  and  thin  animals,  the  estimated  net  energy 
of  Kellner's  maintenance  rations  is  distinctly  less  than  the 
average  maintenance  requirement  found  in  Armsby  and  Fries' 
experiments.  The  mean  of  the  individual  results  of  the  two 
experimenters,  on  16  different  animals,  is  5934  Cals.  The 
average  estimated  net  energy  in  the  maintenance  rations  of  the 
live  weight  experiments  is  somewhat  greater,  viz.,  6181  Cals., 
although  if  the  one  apparently  exceptional  result  obtained  by 
Evvard  be  omitted,  the  average  is  reduced  to  6113  Cals.  The 
maintenance  requirement  of  fat  cattle  is  evidently  distinctly 
greater  than  that  in  the  unfattened  state  but  the  data  are  too 
few  to  permit  the  statement  of  a  trustworthy  average. 

It  appears,  then,  that  the  maintenance  ration  of  mature 
cattle  in  thin  to  medium  condition  must  supply,  on  the  aver- 
age, about  6000  Cals.  of  net  energy  per  thousand  pounds  live 
weight,  although  with  considerable  variations  from  this  average 
in  individual  cases.  That  the  actual  weight  of  feeding  stuffs 
required  to  constitute  a  maintenance  ration,  as  well  as  the 
quantities  of  metabolizable  energy  contained  in  it,  will  vary 
with  the  kinds  of  feeds  used  has  already  been  pointed  out 
(375)  and  is  indeed  sufficiently  obvious. 

The  maintenance  requirement  of  sheep 

382.  Metabolizable  energy  in  maintenance  rations.  —  Data 
regarding  the  maintenance  ration  of  sheep  are  much  less  abun- 
dant than  those  for  cattle  and  no  experiments  have  been  re- 

1  Jour.  Agr.  Research,  3  (1915),  484-485. 

2  Mo.  Expt.  Sta.,  Research  Bui.  7,  p.  120. 

3  U.  S.  Dept.  Agr.,  Farmers'  Bui.  346,  p.  15. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     293 

ported  in  which  the  net  energy  required  for  maintenance,  i.e., 
the  fasting  katabolism,  has  been  determined. 

Respiration  experiments  upon  sheep  have  been  made  by 
Henneberg  and  Stohmann  l  in  1867-1868  on  two  animals,  by 
Henneberg,  Fleisher  and  Mliller  2  in  1872  upon  two  animals, 
by  Hagemann  3  in  1899  on  one  animal,  and  by  Kellner  4  upon 
one  animal.  With  the  exception  of  the  third,  these  were  bal- 
ance experiments  with  a  Pettenkofer  apparatus  and  included 
no  direct  determinations  of  energy  so  far  as  reported.  The 
third  investigation  comprised  a  digestion  and  metabolism 
experiment  in  which  the  energy  of  the  feed  and  the  visible  ex- 
creta was  determined  directly  and  also  42  determinations 
of  the  pulmonary  respiration  with  the  Zuntz  type  of  apparatus. 
(299). 

In  addition  to  the  foregoing  respiration  experiments  there  are 
a  number  of  digestion  experiments  by  Wolff  in  which  the 
live  weight  of  the  animals  was  approximately  maintained,5  and 
Henry  6  reports  a  series  of  experiments  by  Carlyle  and  Klein- 
heinz  with  breeding  ewes  in  which  various  mixed  rations  pro- 
duced an  average  daily  gain  of  0.16  pound  per  head  in  animals 
averaging  145  pounds  in  weight. 

In  these  experiments  the  metabolizable  energy  of  the  rations 
may  be  computed  approximately  from  the  digestible  organic 
matter  in  the  manner  described  in  Chapter  XVII  (774).  In 
the  respiration  experiments  a  correction  for  the  gain  or  loss  by 
the  animal  may  be  made  as  in  the  case  of  Kellner's  experiments 
on  cattle  (381),  while  an  approximate  correction  for  the  gain  in 
the  live  weight  experiments  may  also  be  made. 

The  results,  computed  per  100  Ib.  live  weight,  are  shown  in 
Table  49. 

383.  Net  energy  in  maintenance  rations  of  sheep.  —  As  al- 
ready stated,  no  direct  determinations  of  the  net  energy  re- 
quired for  the  maintenance  of  sheep  are  on  record  and  only 
unsatisfactory  data  are  available  for  computing  it  from  the 
metabolizable  energy  of  maintenance  rations.  For  the  fore- 

1  Neue  Beitrage,  etc.,  pp.  68-286. 

2  Jahresber.  Agr.  Chem.,  16-17  (1873-74),  II,  145. 

3  Arch.  (Anat.  u.)  Physiol. ;   1899,  Suppl.,  p.  138. 

4  Die  Ernahrung.  landw.  Nutzt.,  6th  Ed.,  p.  422. 

5  Compare  U.  S.  Dept.  of  Agr.,  Bur.  Anim.  Indus.,  Bui.  143  (1912),  pp.  4Q-51- 

6  Feeds  and  Feeding,  loth  Ed.,  p.  482. 


294 


NUTRITION  OF  FARM   ANIMALS 


going  experiments,  however,  it  may  be  permissible  to  assume, 
as  in  the  case  of  cattle,  that  about  52.8  per  cent  of  the  metab- 
olizable  energy  of  roughage  and  55  per  cent  of  that  of  mixed 
rations  was  available  for  maintenance.  The  results  of  a  com- 
putation upon  this  basis  are  contained  in  the  last  column  of  the 
following  table.  They  possess  a  certain  degree  of  interest, 
although  obviously  they  are  of  uncertain  value. 

TABLE  49.  —  ENERGY  IN  DAILY  MAINTENANCE  RATIONS  OF  SHEEP 


PER  ioo  LB.  ] 

,IVE  WEIGHT 

Metaboliz- 
able 
Energy 

Net 
Energy 

Respiration  experiments 
Henneberg  and  Stohmann  

Therms 

Therms 
77O 

Henneberg,  Fleischer  and  Miiller     

I  A2O 

78l 

Kellner    

611 

Hagemann   

1.282 

.705 

Average    

I   322 

7IQ 

Live  weight  experiments 
Wolff,  1871,  6  experiments      

I  6^4. 

86l 

Wolff,  1892—1893,  8  experiments 

86^ 

Carlyle  and  Klienheinz  

1-/^O 
I   tJI  3 

8^2 

Average    

I  624 

8<* 

Average  of  all    

i  ^68 

7QI 

384.  Comparison  of  sheep  with  cattle.  —  It  is  of  some  interest 
to  compare  the  maintenance  requirement  of  sheep  with  that  of 
cattle.  Since  the  sheep  is  a  much  smaller  animal  than  the  steer 
it  naturally  requires  relatively  more  feed  in  proportion  to  its 
weight  (345),  as  the  foregoing  figures  show  to  be  the  case. 
As  compared  with  a  steer  weighing  1000  pounds,  ten  sheep  weigh- 
ing ioo  pounds  each  would  require  for  maintenance,  according 
to  the  foregoing  estimates,  about  30  per  cent  more  energy. 
If,  however,  the  comparison  be  made  in  proportion  to  the  two- 
thirds  power  of  the  live  weight,  i.e.,  substantially  in  propor- 
tion to  the  body  surface  (347),  a  very  different  result  is  reached, 
the  maintenance  ration  of  the  sheep  as  thus  computed  amount- 
ing to  little  more  than  60  per  cent  of  that  of  cattle. 


MAINTENANCE  —  THE  ENERGY  REQUIREMENTS     295 

• 

TABLE  50.  —  MAINTENANCE  REQUIREMENTS  OF  CATTLE  AND  SHEEP. 
COMPUTED  IN  PROPORTION  TO  BODY  SURFACE 


NET  ENERGY 
Therms 

Cattle  per  1000  Ib  live  weight    

6.000 

Sheep,  per  1000  Ib.  live  weight     

3.670 

While  such  a  comparison  is  of  course  but  a  rough  approxi- 
mation, it  nevertheless  seems  to  show  conclusively  that  the 
metabolism  of  the  sheep  per  unit  of  surface  is  distinctly  lower 
than  that  of  cattle,  so  that  this  animal  apparently  constitutes 
an  exception  to  the  results  computed  by  E.  Voit  (345)  for 
several  other  species.  The  thick  coat  of  wool,  of  course,  tends 
to  reduce  the  rate  at  which  heat  is  lost  from  the  body  and  it 
seems  at  least  a  plausible  conjecture  that  in  the  course  of  or- 
ganic evolution  the  intensity  of  metabolism  and  the  rate  of  heat 
radiation  may  have  undergone  mutual  adjustment. 

The  maintenance  requirement  of  the  horse 

385.  Net  energy  requirement.  —  Zuntz  and  Hagemann  l 
have  computed  the  fasting  katabolism  of  the  horse  from  the 
results  of  numerous  short  respiration  experiments  with  the 
Zuntz  type  of  apparatus  (299)  by  means  of  a  comparison  identi- 
cal in  principle  with  that  already  described  for  cattle  (374) 
but  carried  out  by  quite  a  different  method,  involving  numerous 
estimates  and  computations. 

They  assume,  on  the  basis  of  experiments  on  man,  that  9  per 
cent  of  the  metabolizable  energy  of  the  digestible  nutrients  consumed 
by  a  horse  is  converted  into  heat  in  the  process  of  digestion,  and  com- 
pute from  their  own  experiments  that  each  gram  of  total  crude  fiber 
consumed  increases  the  heat  production  by  2.086  Cals.  additional, 
exclusive  of  that  due  to  mastication.  For  the  purpose  of  computing 
the  fasting  energy  expenditure,  those  rest  experiments  on  Horse  III 
in  which  the  feed  consisted  of  oats,  hay  and  straw,  are  used.  On 
the  basis  of  a  number  of  short  respiration  experiments  made  within 
the  first  five  hours  after  feeding,  the  total  energy  metabolism  per  day 

1  Landw.  Jahrb.,  27  (1898),  Ergzbd,  III,  271-285  and  422-425. 


296 


NUTRITION  OF  FARM  ANIMALS 


on  the  various  rations  is  computed  from  the  results  of  five  previous 
balance  experiments  on  similar  rations  by  combining  them  in  various 
ratios  according  to  the  proportions  of  oats,  hay  and  straw  consumed. 
From  this  is  subtracted  the  heat  computed  to  have  been  produced  in 
the  digestion  of  the  feed  (not  including  the  work  of  mastication), 
the  remainder  showing,  of  course,  the  katabolism  due  to  internal 
work,  i.e.,  the  net  energy  requirement.1 

Table  51  shows  for  the  eight  experiments  compared  the 
total  estimated  heat  production  per  day,  the  computed  energy 
expenditure  caused  by  the  consumption  of  the  feed,  and  by  dif- 
ference the  energy  expenditure  in  the  fasting  state,  i.e.,  the  net 
energy  requirement  for  maintenance. 

TABLE  51.  —  NET  ENERGY  REQUIREMENT  FOR  MAINTENANCE  OF  HORSE 


ENERGY 

FEED 

o 

EXPENDITURE 

8 

IN  FASTING 

w 

s 

w 

ffi 

f-rl     ffi     9 

8 

PERIODS 

o  o 

o  &  w 

SEASON 

w 

ge 

H  QO 

t 

||| 

w 

g  t> 

3 

o 

d 

t/3 

1 

O  X  !=> 
UHQ 

W 
PH 

<*>'.£>>. 

Kgs. 

Cals. 

Kgs. 

Kgs. 

Kgs. 

Cals. 

Cals. 

Cals. 

a 

428.1 

12,541 

6 

7 

8403 

4138 

80.7 

Winter 

b 

434-1 

11,674 

6 

-6 

7704 

3970 

76.7 

Summer 

e 

450-4 

12,364 

6 

6 

7704 

4660 

87.9 

Winter 

f 

449.1 

11,783 

6 

4-75 

6830 

4953 

93-6 

Summer 

i 

440.1 

11,893 

6 

6 

7704 

4189 

80.2 

Winter 

n 

448.2 

11,407 

4.8 

o 

5.1 

5672 

5735 

108.5 

Summer 

c 

442.2 

12,450 

0 

0 

10.5 

7340 

5110 

97.6 

Summer 

No.  n8c 

434-6 

11,021 

4.8 

0.8 

1.88 

4122 

6899 

133-3 

Winter 

In  the  experiments  with  a  standard  ration  of  6  kgs.  of  oats, 
one  of  straw,  arid  six  (or  seven)  of  hay,  the  average  computed 
fasting  katabolism  per  day  in  three  winter  periods  was  4.33 
Therms,  while  in  a  single  summer  period  it  reaches  the  minimum 
of  3.97  Therms  per  head,  or  4.08  Therms  per  1000  pounds  live 
weight.  Zuntz  and  Hagemann  consider  that  the  latter  amount 
represents  approximately  the  minimum  requirement  for  the  in- 


1  For  a  more  complete  account  of  the  method,  compare  the  writer's  Principles 
of  Animal  Nutrition,  pp.  386-387. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     297 

ternal  work  and  regard  the  higher  figures  obtained  in  the  winter 
experiments  as  indicating  a  stimulation  of  the  heat  production 
by  the  low  temperature  to  which  the  animal  was  exposed ;  i.e., 
they  consider  that  the  experiments  were  made  below  the  critical 
temperature.  The  notably  higher  results  obtained  with  lighter 
rations  they  ascribe  to  a  similar  cause,  viz.,  that  the  heat  arising 
from  the  work  of  digestion,  together  with  that  due  to  the  neces- 
sary internal  work  (fasting  katabolism),  was  insufficient  to 
maintain  the  body  temperature. 

It  must  be  confessed  that,  in  view  of  the  more  active,  tem- 
perament of  the  horse  as  compared  with  cattle  this  relatively 
low  figure  for  the  fasting  katabolism  is  rather  surprising,  and 
the  fact  should  not  be  overlooked  that  it  is  derived  from  short 
periods  in  which  it  is  probable  that  the  animal  was  unusually 
quiet.  It  perhaps  represents  more  nearly  the  physiological 
than  the  economic  minimum  of  net  energy  required  for  main- 
tenance, and  it  would  be  of  much  interest  to  compare  it  with 
the  results  of  24-hour  experiments. 

386.  Metabolizable  energy  in  maintenance  rations.  —  A 
considerable  number  of  experiments  are  on  record  in  which 
the  amount  of  total  digestible  matter  required  for  the  main- 
tenance of  the  horse  has  been  determined. 

The  maintenance  rations  of  cattle  and  sheep  may  be  deter- 
mined with  a  good  degree  of  accuracy  by  varying  the  quantity 
of  feed  given  until  equality  between  income  and  outgo  or  con- 
stancy of  live  weight  is  attained,  but  this  method  is  not  fully 
applicable  to  the  horse.  Owing  to  his  more  active  tempera- 
ment, feed  seems  to  exert  a  greater  stimulus  upon  his  muscular 
activity  than  is  the  case  with  the  more  phlegmatic  ruminants, 
so  that  a  considerable  excess  over  an  actual  maintenance 
ration  may  be  consumed  by  a  horse  and  expended  in  the 
various  minor  activities  noted  in  Chapter  VII  (348),  while 
the  balance  of  income  and  outgo  may  show  neither  gain 
nor  loss,  i.e.,  may  appear  to  show  that  the  ration  is  a  main- 
tenance ration. 

a.  Wolff's  determinations.  —  One  method  of  avoiding  this 
difficulty  and  determining  the  true  maintenance  ration  is  that 
employed  by  Wolff  in  his  extensive  investigations  1  upon  work 
production  by  the  horse  (670,  779).  In  these  experiments  the 

1  Compare  the  writer's  Principles  of  Animal  Nutrition,  pp.  531-535- 


298  NUTRITION  OF  FARM  ANIMALS 

horse  performed  a  measured  amount  of  work  1  which  was  so 
adjusted  in  different  periods  as  to  be  as  nearly  as  possible  in 
equilibrium  with  the  feed  consumed.  This  was  considered  to 
be  the  case  when  the  live  weight  of  the  animal  remained  sub- 
stantially unchanged  for  a  considerable  period  and  when  the 
urinary  nitrogen  did  not  show  an  increase  as  a  consequence 
of  the  additional  work  done  (637).  By  comparing  the  work 
performed  on  a  basal  ration  with  that  which  could  be  done  with 
a  heavier  one,  the  ratio  of  the  work  done  to  the  additional 
feed  consumed  was  established  within  the  limits  of  error  of  the 
method,  this  being  the  prime  object  of  the  experiments.  This 
being  determined,  however,  it  was  a  simple  matter  to  com- 
pute the  amount  of  feed  corresponding  to  the  total  work  per- 
formed, while  the  difference  between  the  latter  and  the  total 
ration  evidently  was  the  maintenance  ration.  From  the  total 
digestible  nutrients  (inclusive  of  crude  fiber)  required  for  main- 
tenance, as  thus  computed  by  Wolff,  the  equivalent  amounts  of 
metabolizable  energy  required  for  maintenance  may  also  be 
computed  approximately  by  the  use  of  Zuntz  and  Hagemann's 
factor  of  3.96  Cals.  per  gram  (776). 

In  Wolff's  earlier  experiments  and  in  those  later  ones  in 
which  approximately  equal  proportions  of  hay  and  grain  were 
consumed,  the  maintenance  ration  was  found  to  be  approxi- 
mately 4200  grams  total  nutrients  per  500  kgs.  live  weight, 
equivalent  to  16.63  Therms.  In  those  later  experiments  (in- 
cluding the  results  of  similar  investigations  by  Grandeau  as  re- 
computed by  Wolff)  in  which  a  larger  proportion  of  grain  was 
fed,  the  total  nutrients  required  for  maintenance  ranged  from 
3600  to  3800  grams,  equivalent  to  from  14.26  to  15.05  Therms. 
In  other  words,  the  amount  of  metabolizable  energy  required 
for  maintenance  varied  with  the  proportion  of  roughage  pres- 
ent, as  would  be  anticipated  from  the  results  with  cattle  re- 
corded on  previous  pages. 

b.  Zuntz  and  Hagemann's  results.  —  From  a  respiration  ex- 
periment at  the  Gottingen  Experiment  Station,  Zuntz  and  Hage- 
mann  compute  the  metabolizable  energy  of  the  maintenance 

1  Wolff's  experiments  were  made  with  a  sweep-power  arranged  to  serve  also  as  a 
dynamometer.  The  actual  measurements  of  the  work  performed,  except  in  the  later 
experiments,  proved  to  be  too  low,  but  Wolff  believes  them  to  be  relatively  correct, 
so  that  the  ratio  between  the  work  as  measured  and  the  additional  feed  required  to 
produce  it  may  still  serve  as  the  basis  of  computation. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     299 

ration  of  the  horse  by  subtracting  from  the  total  digested 
nutrients  the  carbohydrate  equivalent  of  the  protein  and  fat 
gained  by  the  animal,  disregarding  the  possible  stimulating 
effect  of  the  feed.  In  this  way,  they  find  for  the  maintenance 
ration  2955.4  grams  total  digested  nutrients  per  head,  equiva- 
lent to  11.70  Therms  or  12.1  Therms  per  1000  pounds  live  weight, 
a  result  notably  lower  than  Wolff's.  This  difference  is  ascribed 
by  Zuntz  and  Hagemann  to  the  larger  content  of  crude  fiber  in 
Wolff's  rations,  the  work  of  digestion  of  this  ingredient  as  es- 
timated by  them  (777)  very  nearly  accounting  for  the  differ- 
ence. 

c.  Muntz's  experiments.  —  Muntz  1  in  1878-1879  attempted  to 
determine  the  maintenance  ration  of  the  horse  by  starting  with 
an  insufficient  ration  and  gradually  increasing  it  until  an  equilib- 
rium between  feed  and  live  weight  was  secured,  seeking  in  this 
manner  to  eliminate  the  stimulating  effect  of  excess  feed  (392). 
The  trials  were  made  on  the  horses  of  the  Paris  Omnibus  Com- 
pany, their  work  ration  being  known  from  previous  experiments. 
He  found  that  a  ration  equal  to  -f%  of  the  work  ration  and 
which  may  be  estimated  to  contain  12.1  Therms  of  metaboliz- 
able  energy  per  1000  pounds  live  weight  was  slightly  more  than 
sufficient  for  maintenance. 

d.  Grandeau  and  LeClerc's  results.  —  Grandeau  and  LeClerc,2 
in  addition  to  the  experiments  mentioned  in  connection  with 
Wolff's  results,  fed  five  cab  horses  a  ration  of  8  kgs.  of  hay 
during  a  total  of  14  periods  of  a  month  each  (one  to  five  periods 
for  each  animal)  during  each  of  which  the  digestibility  of  the 
ration  was  determined.     On  the  average  of  all  the  periods,  the 
results  per  day  and  head  were  as  follows :  - 

Total  digestible  nutrients  (fat  X  2.4) 2783.7    grams 

Equivalent  metabolizable  energy  at  3.96  Cals.  per 

gram      .' 11.03  Therms 

Daily  gain  in  weight 0.19  kg. 

Average  live  weight 393.6    kgs. 

The  foregoing  ration,  which  was  evidently  somewhat  more 
than  a  maintenance  ration,  is  equivalent  to  13.1  Therms  of 
metabolizable  energy  per  1000  pounds  live  weight.  This  is 

1  Annales  de  PInstitut  National  Agronomique,  Tome  3,  1876-1879. 

2  L'alimentation  du  Cheval  de  Trait,  1883,  in. 


3oo 


NUTRITION  OF  FARM  ANIMALS 


materially  less  than  was  obtained  in  Wolff's  earlier  experiments 
with  hay  and  about  the  same  as  that  found  by  him  and  by 
Zuntz  and  Hagemann  for  rations  containing  much  grain. 

The  following  summary  of  the  data  regarding  the  metaboliz- 
able  energy  required  for  maintenance  by  the  horse  shows  a 
considerable  range  of  variation  which  is  only  partially  expli- 
cable by  the  varying  proportions  of  grain  and  roughage  con- 
tained in  the  rations. 

TABLE  52.  —  MAINTENANCE  RATIONS  OF  THE  HORSE 


EXPERIMENTER 

GRAIN  TO  ONE 

OF  ROUGHAGE 

METABOLIZABLE 
ENERGY  PER 

1000   LB.    LIVE 

WEIGHT 

Wolff    

(Approximate) 
I  O 

Therms 
IS.6 

Wolff  and  Grandeau  and  LeClerc      .     .     . 
Zuntz  and  Hagemann 

2.4 
I  8 

13-6 
12.  1 

Miintz      

0.7 

12.  1 

Grandeau  and  LeClerc    
Wolff    

hay  only 
hay  only 

I3-I 
I7.I 

387.   Metabolizable  compared  with  net  energy  requirement. 

—  The  net  energy  required  for  maintenance,  as  with  other  ani- 
mals, equals  of  course  the  fasting  katabolism.  This  Zuntz  and 
Hagemann  compute,  in  the  manner  already  described  (385)  to 
be  4.1  Therms  per  thousand  pounds  live  weight.  As  was 
there  pointed  out,  however,  those  of  their  experiments  in  which 
the  external  temperature  was  lower  or  the  amount  of  feed  less 
gave  higher  results.  The  latter  was  also  notably  the  case  in 
earlier  experiments  in  which  still  lighter  rations  were  fed. 

On  the  average  of  the  eight  most  satisfactory  experiments  out  of 
twelve  *  on  Horse  II  the  total  katabolism  per  day  and  head  was  11.027 
Therms  upon  a  ration  consisting  of  3.5  Kgs.  of  oats,  0.5  of  straw  and 
2.5  of  hay.  Computed  in  the  same  manner  as  in  Table  51,  the 
expenditure  of  energy  in  the  digestion  of  this  ration  is  equal  to 
3782  Cals.,  which  leaves  a  remainder  of  7244  Cals.,  equivalent  to 
140.3  Cals.,  per  square  centimeter  of  surface.  This  is  a  higher 
figure  than  any  of  those  contained  in  Table  51,  although  the  total 
katabolism  was  not  notably  different. 

1  Landw.  Jahrb.,  18,  i ;  27,  Ergzbd.  Ill,  356-357- 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     301 

The  authors  conclude,  therefore,  that  when  the  amount  of 
heat  liberated  by  the  digestive  work  is  small  the  lack  is  com- 
pensated for  by  an  increased  katabolism  of  body  tissue.  Their 
final  result  is  that  their  animal  required  per  head  at  least  n.oo 
Therms  of  heat  to  maintain  his  body  temperature.  In  other 
words,  this  is  the  minimum  of  metabolizable  energy  which 
must  be  contained  in  a  maintenance  ration,  since  if  less  be 
present,  even  although  the  ration  supply  the  requisite  amount 
of  net  energy,  body  tissue  would  still  be  katabolized  for  the 
production  of  the  necessary  heat.  Computed  per  thousand 
pounds  live  weight,  Zuntz  and  Hagemann's  estimated  main- 
tenance requirement  is :  — 

Net  energy  for  internal  work 4.1  Therms 

Additional  required  for  heat  production 7.8  Therms 

Total  metabolizable  energy  required 11.9  Therms 

In  computing  a  ration  for  the  actual  maintenance  of  the 
horse  at  rest,  it  is  necessary,  according  to  these  figures,  to  con- 
sider not  only  whether  it  supplies  net  energy  equal  to  the  fast- 
ing katabolism  but  also  whether  it  contains  sufficient  metab- 
olizable energy  to  support  the  necessary  heat  production.  On 
the  other  hand  no  such  allowance  need  ordinarily  be  made  in 
computing  work  rations.  The  horse  when  at  work  is  producing 
an  excess  of  heat  (compare  Chapter  XIV) ,  and  during  the  work- 
ing hours  no  expenditure  of  feed  energy  for  the  sake  of  heat 
production  would  be  called  for,  while  any  ordinary  working 
ration  would  probably  contain  a  considerable  surplus  of  me- 
tabolizable energy  over  the  maintenance  demand  during  the 
hours  of  rest. 

The  maintenance  requirement  of  fowls 

388.  Net  energy  requirements.  —  Gerhartz  l  has  measured 
the  net  energy  requirement  of  fowls  by  means  of  a  num- 
ber of  respiration  experiments  with  the  Regnault-Reiset  type 
of  apparatus  (298)  upon  two  fasting  hens.  He  has  also  com- 
puted the  fasting  katabolism  from  a  number  of  respiration  ex- 
periments in  which  the  animals  were  fed  by  subtracting  from 
the  total  metabolism  that  computed  to  have  been  due  to  the 

1  Landw.  Jahrb.,  46  (1914),  797. 


302 


NUTRITION  OF   FARM  ANIMALS 


consumption  of  the  feed  —  i.e.,  by  substantially  the  same  gen- 
eral methods  used  by  Zuntz  and  Hagemann  for  the  horse  (385). 
His  results,  computed  per  thousand  square  centimeters  of  body 
surface  and  also  per  5  pounds  live  weight  in  proportion  to  the 
f  power  of  the  latter,  were  as  follows :  — 

TABLE  53.  —  NET  ENERGY  FOR  MAINTENANCE  OF  HENS 


LIVE 
WEIGHT 

PER  1000 
SQ.  CM. 
BODY 
SURFACE 

PER  5 
POUNDS 
.   LIVE 
WEIGHT 

In  fasting  experiments 
Minimum  when  not  laying  
Average  when  not  laying      
Average  when  laying  . 

Grins. 

2350 
2273 
2T.ZO 

Cals. 

58.37 
76.77 

Q-l.  6? 

Cals. 
57-Qi 
76.75 
01.45; 

Computed  from  experiments  with  feed 
Minimum  when  not  laying  

2137 

<!2.  08 

CC.I2 

Average  when  not  laying     
Average  when  laying  

2046 
2023 

62.16 

87.03 

66.58 
93-91 

It  would  appear  from  the  figures  that  the  average  main- 
tenance requirement  of  a  5-pound  hen  may  be  estimated  at  ap- 
proximately 72  Cals.,  while  in  periods  of  minimum  muscular  ac- 
tivity it  may  fall  as  low  as  56  Cals.  The  much  higher  figure 
(93  Cals.)  obtained  in  the  periods  when  the  hen  was  laying 
does  not  represent  maintenance  simply,  but  includes  also  the 
energy  expended  in  the  formation  of  the  egg.  As  with  all  small 
animals,  the  katabolism  of  the  hen  per  unit  weight  is  high,  but 
when  computed  per  unit  of  surface  it  does  not  differ  greatly 
from  that  of  other  species. 

389.  Metabolizable  energy  in  maintenance  rations.  —  Ger- 
hartz  also  determined  the  amount  of  feed  required  to  main- 
tain the  live  weight  of  his  fowls  and  computes  the  correspond- 
ing amounts  of  metabolizable  energy  to  have  been  per  1000  sq. 
cm.  body  surface. 


Rest  period 102  Cals. 

Molting  period 107  Cals. 

f   72  Cals. 
'     '     '     '  \  97  Cals. 


Brooding  period 


Average 95  Cals. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS     303 


Summary 

390.  For  convenience  of  reference,  the  average  results  re- 
garding the  energy  required  for  the  maintenance  of  the  com- 
mon species  of  farm  animals  as  recorded  in  the  foregoing  pages 
are  brought  together  in  the  following  table.  For  live  weights 
other  than  those  stated  the  maintenance  requirement  may  be 
computed  in  proportion  to  the  surface  in  the  manner  described 
in  Chapter  VII  (347). 


TABLE  54.  —  ENERGY  REQUIREMENTS  FOR  MAINTENANCE 


NET  ENERGY 
Therms 

METABOLIZABLE 
ENERGY 

Therms 

Swine,  per  100  Ib.  live  weight  .... 
Cattle,  per  1000  Ib.  live  weight 
Unfattened    
Fattened 

1.25 

6.00 
7  QS  (?) 

1-53 

10.47 
I?  cq 

Sheep,  per  100  Ib.  live  weight  .... 
Horses,  per  1000  Ib.  live  weight  .     .     . 
Hens,  per  5  Ib.  live  weight       .... 

0-79 
4.10 
0.072 

1-37 
II.QO 
O.OQS 

As  pointed  out  at  the  beginning  of  this  section  (376),  the 
foregoing  figures  express  an  economic  rather  than  a  physio- 
logical requirement  for  energy.  Besides  the  absolute  energy 
requirement  in  a  state  of  complete  rest,  they  include  the  energy 
expended  in  divers  forms  of  incidental  muscular  work,  of  which 
one  of  the  most  important,  in  farm  animals,  appears  to  be  that 
of  standing  (349).  The  average  for  swine  was  obtained  from 
experiments  in  which  the  animals  were  lying  during  most  or  all 
of  the  time.  The  average  for  cattle,  as  noted,  has  been  com- 
puted to  twelve  hours  standing,  while  that  for  the  horse  rep- 
resents the  katabolism  when  standing  quietly. 

Moreover,  even  with  the  limitations  just  indicated,  the  results 
represent  averages  from  which  the  energy  expenditure  of  the 
individual  animal  may  differ  considerably.  Such  averages  are 
useful  as  a  basis  for  computing  feed  requirements  and  rations, 
but  it  should  be  clearly  understood  that  they  are  by  no  means 
physiological  constants  which  can  be  applied  to  all  animals 


3°4 


NUTRITION  OF   FARM   ANIMALS 


indiscriminately  or  used  as  a  basis  for  exact  computations  of 
the  effects  of  feeds  in  individual  cases. 


§  3.    FACTORS  AFFECTING  THE  MAINTENANCE  REQUIREMENT 

Certain  conditions  which  affect  the  energy  expenditure  of 
the  fasting  animal,  and  therefore  the  amount  of  net  energy 
required  for  maintenance,  have  already  been  discussed  in  Chap- 
ter VII  (345-357) ,  while  a  few  others  may  be  more  conveniently 
considered  at  this  point. 

391.  Temperament.  —  The  nervous,  restless  animal  is  con- 
tinually expending  energy  in  a  variety  of  unnecessary  move- 
ments which  may  very  materially  increase  the  amount  of  energy 
needed  for  his  maintenance  as  compared  with  that  required 
by  the  quieter  and  more  phlegmatic  animal.  There  can  be  little 
question  that  those  differences  between  the  maintenance  re- 
quirements of  different  animals  which  are  ascribed  somewhat 
vaguely  to  "  individuality  "  are  due  to  a  large  extent  to  vary- 
ing amounts  of  muscular  activity. 

Thus  in  Armsby  and  Fries'  determinations 1  of  the  maintenance 
requirement  of  cattle  (380)  the  two  animals  designated  as  A 
and  B  were  respectively  a  pure-bred  beef  animal  and  a  scrub,  the 
latter  having  more  or  less  dairy  blood  and  being  of  a  decidedly 
more  nervous  disposition  than  the  animal  A.  The  difference 
in  the  requirements  of  the  two  animals,  as  shown  by  the  follow- 
ing comparison,  may  be  reasonably  ascribed  to  this  differ- 
ence in  temperament. 


TABLE  55.  —  NET  ENERGY  REQUIREMENT  FOR  MAINTENANCE 


YEAR 

BEEF 
STEER 
A 

SCRUB 
STEER 
B 

IQCX    . 

Therms 
^•873 

Therms 
6.052 

IQO6 

6  272 

6  3CK 

1907    

4-723 

6.067 

Average 

^.6?3 

6.141 

U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  128  (1911),  p.  53. 


MAINTENANCE  —  THE  ENERGY  REQUIREMENTS      305 

Like  the  temperament,  any  external  conditions  tending  to 
affect  the  degree  of  muscular  activity  will  also  tend  to  affect 
the  maintenance  requirement.  The  steer  confined  in  a  stall, 
for  example,  may  take  less  muscular  exercise,  and  therefore 
require  less  energy  for  maintenance,  than  one  simply  confined 
to  a  pen  or  open  yard.  The  animal  comfortably  bedded  and 
thereby  induced  to  spend  much  of  his  time  lying  down  will 
consume  a  smaller  proportion  of  his  feed  for  maintenance  than 
one  kept  under  less  comfortable  conditions.  Any  sort  of 
excitement  is  likely  to  be  paid  for  by  increased  muscular  ac- 
tivity and  correspondingly  increased  consumption  of  feed  for 
maintenance. 

392.  The  plane  of  nutrition.  —  It  is  somewhat  generally  be- 
lieved that  the  amount  of  feed  necessary  for  maintenance  varies 
with  the  plane  of  nutrition  on  which  the  animal  is  kept.  By 
this  is  meant  that  an  animal  which  has  been  highly  fed  for 
some  time  will  require  a  larger  amount  of  feed  for  maintenance 
than  a  similar  animal  which  has  been  sparsely  fed  and  is  in 
a  more  or  less  reduced  condition.  Thus,  Waters 1  writes : 
"  Apparently  the  animal  organism  when  kept  for  a  long 
period  of  time  on  a  low  nutritive  plane,  as  in  the  case  of  main- 
tenance animals,  gets  on  a  more  economical  basis  than  when 
more  liberally  fed.  For  example,  if  we  reduce  the  feed  of  an 
animal  that  has  been  previously  liberally  nourished  to  a  point 
where  for  a  month  or  more  there  is  a  small  loss  in  weight,  an 
equilibrium  will  later  be  established  and  subsequently  the 
animal  may  increase  in  weight,  the  quantity  and  quality  of 
the  feed  remaining  the  same.  Thus  a  ration  that  was  insuf- 
ficient to  sustain  live  weight  at  first  may  be  capable  later  of 
maintaining  the  animal  at  a  stationary  body  weight,  and  still 
later  of  causing  an  increase  in  weight.  Digestion  experiments 
with  a  number  of  animals  indicate  that  a  part  of  this  is  due  to 
the  more  complete  digestion  of  the  feed  by  the  animal  on  a  low 
nutritive  plane,  but  so  far  as  the  experiments  have  thus  far  pro- 
gressed there  does  not  seem  to  have  been  a  sufficient  increase 
in  the  degree  to  which  the  feed  has  been  digested  to  account 
for  all  the  increased  efficiency  in  the  ration  noted."  2 

Comparatively  little  experimental  confirmation  of  these  re- 
sults has  as  yet  been  published,  although  respiration  experi- 

1  Proc.  Soc.  Prom.  Agr.  Sci.,  1908,  p.  96.         2  Compare  Chapter  XVI,  §  3  (722). 
X 


306  NUTRITION  OF  FARM   ANIMALS 

merits  on  dogs  by  Kleinert 1  and  by  Schlossmann  and  Mursch- 
hauser2  seem  to  point  in  the  same  direction. 

Observations  made  by  Zuntz  and  Hagemann 3  on  the  horse 
appear  suggestive  in  this  connection.  In  a  series  of  respiration 
experiments  they  have  confirmed  the  common  observation  that 
a  surplus  of  feed  above  the  maintenance  requirement  stimu- 
lates the  muscular  activity  and  restlessness  of  this  animal,  so 
that  a  ration  may  be  considerably  more  than  sufficient  to  main- 
tain the  animal  when  standing  quietly  in  the  stall  and  yet 
give  rise  to  no  increase  in  weight  under  ordinary  conditions. 
A  similar  stimulating  effect  of  the  feed  upon  the  minor  muscular 
movements  of  cattle,  expecially  while  standing,  seems  to  be  in- 
dicated by  the  experiments  of  Armsby  and  Fries  (367  e).  It 
seems  possible  that  part,  at  least,  of  the  diminution  of  the  main- 
tenance requirement  observed  by  Waters  may  have  been  due 
to  a  voluntary  restriction  of  motion  on  the  part  of  the  animals 
on  the  low  nutritive  plane. 

In  attempting  to  determine  experimentally  the  minimum 
maintenance  requirement  it  is  evidently  the  safer  method  of 
procedure,  especially  with  the  horse,  to  approach  the  main- 
tenance point  by  gradually  increasing  a  sub-maintenance  ration, 
as  in  Miintz's  experiments  on  the  horse  (386  c)  and  those  of 
Armsby  and  Fries  on  cattle  (374)  rather  than  by  the  gradual 
reduction  of  a  supermaintenance  ration. 

393.  Fattening.  —  That  fat  animals  have  a  relatively  greater 
maintenance  requirement  than  thin  ones  seems  to  be  fairly 
well  established  for  cattle  by  the  experiments  of  Kellner  and 
of  Evvard,  the  results  of  which  are  recorded  in  Table  48  (381). 

One  obvious  reason  why  the  maintenance  requirement  per 
head  should  be  greater  for  a  fattened  animal  than  for  the  same 
animal  before  fattening  is  the  greater  muscular  effort  expended 
in  standing,  due  to  the  greater  weight  to  be  supported.  Zuntz 
and  Hagemann,  in  experiments  upon  the  horse  carrying  weight 
on  its  back,  found  that  this  increase  was  proportional  to  the 
amount  of  weight  added  (665).  If  this  be  true  generally,  then 
that  portion  of  the  metabolism  due  to  standing  will  increase 
more  rapidly  than  the  body  surface.  In  Armsby  and  Fries' 
experiments  on  unfatted  cattle,  however,  the  energy  expendi- 

1  Ztschr.  Biol.,  61  (1913),  346.  s  Biochem.  Ztschr.,  53  (1913),  265. 

3Landw.  Jahrb.  27  (1898),  Ergzbd.  Ill,  211,  236. 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS      307 

ture  due  to  standing  12  hours  amounted  to  only  about  15  per 
cent  of  the  total  daily  metabolism.  The  increase  in  the  main- 
tenance requirement  per  unit  of  surface  which  is  indicated  by 
Kellner's  results  is  considerably  greater  than  would  be  computed 
on  this  basis  and  the  same  is  true  of  Evvard's  fat  animals,  the 
difference  becoming  greater  as  the  animals  grew  fatter. 

394.  Age.  —  The  maintenance  requirement  of  a  young  ani- 
mal is  naturally  smaller  per  head  than  that  of  an  older  animal 
on  account  of  the  difference  in  size.  Whether  there  is  any 
difference  in  the  relative  requirement,  that  is,  in  the  require- 
ment computed  to  uniform  weight  or  surface,  is  not  altogether 
clear,  few  specific  results  on  farm  animals  being  on  record. 
Evvard's  results  on  yearlings  (381)  are  somewhat  higher  than 
most  of  those  which  have  been  obtained  with  mature  cat- 
tle, although,  of  course,  these  figures  do  not  relate  to  the  same 
individuals  at  different  ages.  Armsby  and  Fries  1  in  a  series  of 
respiration  calorimeter  experiments  upon  the  same  two  animals 
in  three  successive  years  found  with  their  full-blood  steer  a 
marked  decrease  in  the  maintenance  requirement  as  a  yearling 
and  as  a  three-year  old,  when  corrected  to  a  uniform  number  of 
hours  standing  and  computed  in  proportion  to  the  two-thirds 
power  of  the  weight.  With  the  scrub  steer,  on  the  other 
hand,  no  distinct  decrease  of  the  maintenance  requirement  was 
observed. 

Somewhat  extensive  data  are  on  record  regarding  the  metabolism 
of  man  at  different  ages.  A  summary  of  these  by  Tigerstedt 2  seems 
to  show  clearly  that  the  metabolism  per  unit  of  surface  diminishes, 
although  not  very  rapidly,  from  youth  to  maturity.  In  view  of  the 
relatively  slow  growth  of  man,  these  results  are  comparable  to  such 
as  might  be  obtained  during  the  first  six  to  twelve  months  of  the  life 
of  ordinary  domestic  animals  and  for  these  ages  there  are  no  satis- 
factory determinations  of  the  maintenance  requirement. 

If  it  be  true  that  the  maintenance  requirement  of  a  young 
animal  is  relatively  greater  than  that  of  an  older  one,  this  may 
fairly  be  presumed  to  be  due  to  a  considerable  extent  to  the 
greater  muscular  activity  usually  exhibited  by  young  animals, 
which,  as  already  pointed  out,  notably  increases  the  body 
katabolism. 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  128. 

2  Nagel's  Handbuch  der  Physiologic  des  Menschen,  I,  469. 


308  NUTRITION  OF   FARM  ANIMALS 

§  4.   THE  RELATION  or  THE  MAINTENANCE  REQUIREMENT 
TO  EXTERNAL  TEMPERATURE 

While  the  temperature  to  which  an  animal  is  exposed  is  but 
one  among  other  factors  which  may  affect  its  maintenance  re- 
quirement, the  somewhat  complicated  relations  involved  seem 
to  warrant  a  separate  discussion. 

395.  Feed  consumption  lowers  the  critical  temperature.  —  In 
discussing  the  influence  of  temperature  upon  the  fasting  katab- 
olism  (350-357)  it  was  shown  that  for  the  fasting  animal  there 
is  a  certain  external  temperature  (or  more  strictly,  thermal  en- 
vironment), called  the  "  critical  temperature,"  at  which  the 
heat  production  incidental  to  the  necessary  fasting  katabolism 
just  balances  the  unavoidable  loss  by  radiation,  conduction  and 
evaporation,  so  that  the  body  temperature  is  just  maintained. 
Above  this  temperature,  the  fasting  animal  has  a  surplus  of 
heat  which  it  gets  rid  of  by  means  of  the  physical  regulation. 
Below  the  critical  temperature,  on  the  other  hand,  its  katab- 
olism is  increased  beyond  that  necessary  for  the  internal  work 
of  the  body  in  order  to  supply  the  necessary  amount  of  heat ; 
i.e.,  the  energy  expenditure  is  augmented. 

As  has  been  shown  (365),  however,  the  consumption  of  feed 
results  in  increasing  the  heat  production  of  an  animal.  When 
an  animal  is  fed,  therefore,  it  has  two  sources  of  heat :  first,  as 
in  the  fasting  state,  the  heat  resulting  from  the  katabolism  inci- 
dent to  the  necessary  internal  work  of  the  body,  and  second,  in 
addition  to  this,  the  heat  generated  by  the  so-called  "  work  of 
digestion."  Under  these  conditions,  with  more  heat  being 
produced  in  the  body  as  the  result  of  feed  consumption,  it  is 
obvious  that  the  animal  can  withstand  a  greater  cooling  effect 
of  its  surroundings  without  being  compelled  to  katabolize  body 
substance  to  maintain  its  body  temperature.  In  other  words, 
the  "  critical  temperature "  is  lowered.  Furthermore,  the 
greater  the  amount  of  feed  consumed  the  lower  is  the  point  to 
which  the  external  temperature  can  fall  without  reaching  the 
critical  point,  so  that  animals  receiving  heavy  rations  in  pro- 
ductive feeding  can  withstand  more  cold  than  those  on  simple 
maintenance.  Conversely,  for  any  particular  temperature 
there  will  be  a  definite  amount  of  any  given  feed  the  consumption 
of  which,  together  with  the  katabolism  required  for  the  internal 


MAINTENANCE  — THE   ENERGY  REQUIREMENTS      309 


work,  will  give  rise  to  the  production  of  an  amount  of  heat 
just  sufficient  to  balance  the  unavoidable  loss  of  heat  to  the 
surroundings. 

This  influence  of  the  quantity  of  feed  is  well  illustrated  by 
the  following  tabulation  of  Rubner's  results  upon  a  dog  at 
different  temperatures  and  consuming  different  amounts  of 
meat. 

TABLE  56.  —  INFLUENCE  OF  EXTERNAL  TEMPERATURE  ON  HEAT 
PRODUCTION 


HEAT  PRODUCTION  PER  KG.  BODY  WEIGHT 

TEMPERATURE 

Fasting 

Fed  100  Grms. 
Meat 

Fed  200  Grms. 
Meat 

Fed  320  Grms. 
Meat 

Cals. 

Cals. 

Cals. 

Cals. 

7°C. 

86.4 

— 

77-7 

87.9 

15°  C. 

63.0 

— 

— 

86.6 

20°  C. 

55-9 

55-9 

57-9 

76.3 

25°  C. 

54-2 

55-5 

64.9 

30°  C. 

56.2 

55-6 

63-4 

83.0 

The  amount  of  feed  required  to  just  offset  the  cooling  effect 
of  a  low  temperature  might  be  called  the  critical  amount  of 
feed  for  that  temperature.  It  will  obviously  be  less  the  greater 
the  proportion  of  its  metabolizable  energy  which  is  dissipated 
as  heat. 

For  example,  in  discussing  the  relative  amounts  of  different 
feeds  necessary  for  maintenance  (375)  it  was  stated  that  either 
13.83  Ib.  of  mixed  hay  or  9.07  Ib.  of  mixed  grain  and  alfalfa 
hay  would  yield  approximately  6.0  Therms  of  net  energy,  and 
would  therefore  constitute  a  maintenance  ration  for  a  1000- 
pound  steer.  The  amounts  of  metabolizable  energy  contained 
in  these  two  rations,  however,  would  be  different,  viz. :  — 


13.83  Jb.  mixed  hay 

~  ""•  Ib.  mixed  grain  and  alfalfa  hay 


9.07 


12.01  Therms 
10.69  Therms 


Since  both  are  maintenance  rations,  the  animal  would  neither 
gain  nor  lose  energy  and  all  the  metabolizable  energy  of  the 
feed  would  be  finally  converted  into  heat  in  both  cases.  The 


310  NUTRITION  OF  FARM  ANIMALS 

animal  on  the  exclusive  hay  ration,  therefore,  would  have  at 
his  disposal  1.32  Therms  more  heat  than  the  other  and  accord- 
ingly could  withstand  a  lower  temperature  without  drawing  on 
his  body  for  fuel. 

396.  Net  energy  below  critical  temperature.  —  Down  to  the 
critical  temperature  which  corresponds  to  the  particular  amount 
and  kind  of  feed  consumed,  in  accordance  with  the  facts  brought 
out  in  the  previous  paragraphs,  only  part  of  the  metaboliz- 
able  energy  serves  to  maintain  the  animal.  The  remainder  is 
virtually  expended  in  the  "  work  of  digestion  "  and  converted 
into  heat,  and  this  heat,  since  not  needed  by  the  animal,  be- 
comes an  excretum  and  is  gotten  rid  of.  If,  however,  the  ex- 
ternal temperature  falls  below  the  critical  point  the  case  is  dif- 
ferent. Heat  resulting  from  the  ingestion  of  feed  is  just  as  useful 
as  heat  from  any  other  source  for  keeping  the  body  warm. 
Under  these  conditions,  therefore,  all  the  metabolizable  energy 
of  the  feed  may  be  of  use.  Part  of  it  (the  net  energy)  is  used 
directly  for  supporting  the  necessary  internal  work  of  the  body, 
while  the  remainder  prevents  the  necessity  of  katabolizing  tis- 
sue for  the  sake  of  heat  production  and  is  therefore  indirectly 
of  use.  In  other  words,  the  heat  resulting  from  the  consumption 
of  feed  may  be  substituted  for  heat  which  would  otherwise 
have  to  be  obtained  by  the  katabolism  of  tissue.  When  the 
external  temperature  falls  so  low  that  all  the  heat  produced  by 
the  digestive  work  is  required  for  this  purpose,  obviously  all 
the  metabolizable  energy  of  the  ration  is  of  use  directly  or  in- 
directly to  prevent  loss  of  energy  from  the  body  and  therefore 
all  of  it  appears  to  be  net  energy. 

Thus,  if  the  ration  of  mixed  grain  and  alfalfa  hay  used  as  an  illus- 
tration in  the  previous  paragraph  be  fed  to  a  steer  whose  surround- 
ings are  kept  at  the  critical  temperature  for  the  fasting  animal,  the 
6.0  Therms  of  net  energy  which  the  ration  supplies  will  be  used  to 
support  the  internal  work  of  the  body,  and  the  heat  thus  produced 
will  be  just  sufficient  to  maintain  the  body  temperature,  while  the 
remaining  4.69  Therms  of  metabolizable  energy  will  be  expended  in 
superfluous  heat  production.  Suppose,  now,  that  the  external  tem- 
perature falls  to  a  point  at  which  the  fasting  katabolism  would  be 
10.69  Therms  instead  of  6.0  Therms,  i.e.,  at  which  this  amount  of 
heat  is  necessary  to  maintain  the  normal  body  temperature.  The 
necessary  internal  work  of  the  body  still  yields  6.0  Therms,  as  before, 


MAINTENANCE  — THE  ENERGY  REQUIREMENTS      311 

while  the  additional  4.69  Therms  of  heat  resulting  from  the  "work  of 
digestion"  will  be  of  use  in  keeping  the  animal  warm  and  will  obviate 
the  necessity  of  its  katabolizing  body  substance  for  that  purpose. 
All  the  metabolizable  energy  of  the  ration,  therefore,  contributes  to 
the  maintenance  of  the  animal  under  these  conditions,  part  directly 
and  part  indirectly,  and  the  availability  is  apparently  100  per  cent, 
while  the  real  availability  for  the  physiological  processes  in  the  body 
is  only  56  per  cent.  If  the  experiment  were  made  at  an  intermediate 
temperature  at  which  the  fasting  metabolism  would  be  8.0  Therms, 
then  2.0  Therms  of  the  heat  due  to  the  "work  of  digestion"  would  be 
of  use  in  maintaining  the  body  temperature  and  the  apparent  avail- 
ability would  be  75  per  cent,  i.e.,  the  result  would  be  a  mixed  one. 
Evidently,  the  actual  expenditure  of  energy  in  the  "  work  of  digestion," 
and  its  complement,  the  net  energy,  can  be  determined  only  by  ex- 
periments made  above  the  critical  temperature. 

397.  Bearing  on  maintenance  ration.  — The  foregoing  facts 
render  it  apparent  that  in  the  case  of  an  animal  on  a  main- 
tenance ration  the  external  temperature  may  fall  considerably 
below  the  critical  temperature  for  the  same  animal  when  fast- 
ing before  there  is  any  increase  in  the  amount  of  feed  actually 
required  for  maintenance.  Only  when  the  temperature  falls  so 
low  that  all  the  metabolizable  energy  of  the  ration  is  being 
utilized,  directly  or  indirectly,  to  maintain  the  body  heat  will  a 
further  drop  in  the  temperature  call  for  greater  feed  consumption, 
i.e.,  for  an  increase  in  the  maintenance  ration.  These  considera- 
tions may  affect  the  computation  of  actual  maintenance  rations. 
An  example  of  this  is  afforded  by  Zuntz  and  Hagemann's 
results  upon  the  maintenance  requirements  of  the  horse  (387). 
According  to  these  investigators,  a  horse  weighing  1000  pounds 
requires  only  4.1  Therms  of  net  energy  per  day  for  maintenance, 
but  the  body  also  needs  to  be  supplied  with  an  additional  7.8 
Therms  of  heat,  making  a  total  of  11.9  Therms  daily,  to  bal- 
ance the  loss  of  heat  from  the  body.  If,  therefore,  a  mainte- 
nance ration  be  computed  supplying  the  necessary  4.  i  Therms  of 
available  energy,  it  still  remains  to  be  considered  whether  the 
heat  arising  from  the  so-called  "  work  of  digestion  "  will  supply 
the  remaining  7.8  Therms  of  heat  required.  If  it  does  not,  the 
difference,  according  to  Zuntz  and  Hagemann,  will  be  made  up 
by  the  katabolism  of  body  tissue,  as  is  illustrated  in  several  of 
their  experiments,  and  the  ration  will  not  maintain  the  animal 
although  it  contains  net  energy  equal  to  the  fasting  katabolism. 


312  NUTRITION  OF  FARM  ANIMALS 

To  put  the  matter  in  another  way,  Zuntz  and  Hagemann  con- 
sider that  when  receiving  the  ordinary  maintenance  ration  the 
critical  external  temperature  for  the  horse  is  comparatively  high, 
so  that,  for  example,  a  ration  which  is  sufficient  for  maintenance 
in  summer  may  be  insufficient  in  winter,  not^because  it  contains 
any  less  available  energy  but  because  it  fails  to  meet  the  de- 
mand for  heat. 

Tangl's  experiments  (377)  showed  that  the  critical  tempera- 
ture for  swine  is  likewise  comparatively  high  (68°-73°F.), 
while  the  expenditure  of  energy  in  digestion  by  these  animals, 
especially  when  fed  chiefly  or  wholly  on  concentrates,  is  likely 
to  be  less  than  that  of  ruminants.  Exposure  to  low  tempera- 
tures, therefore,  may  be  expected  to  increase  the  actual  main- 
tenance ration  of  swine,  and  this  belief  seems  to  be  confirmed  by 
the  reported  results  upon  the  influence  of  exposure  on  the  gains 
of  fattening  swine.1  It  also  seems  possible  that  part  of  the  very 
wide  variations  observed  in  the  amount  of  metabolizable  energy 
required  for  the  maintenance  of  swine  (378)  may  be  due  to  dif- 
ferences in  the  temperature  at  which  the  experiments  were  made. 

Experiments  on  cattle  by  Armsby  and  Fries  have  shown  that 
at  temperatures  in  the  neighborhood  of  63°  F.,  the  feed  may  be 
reduced  very  considerably  below  the  maintenance  ration  with- 
out any  indication  of  an  increased  katabolism  for  the  sake  of 
heat  production.  A  single  series  of  comparisons  at  a  somewhat 
lower  temperature  (56°  F.)  also  showed  no  increase  in  the  katab- 
olism, even  on  rations  much  below  maintenance.  No  exact 
experiments  at  lower  temperatures  have  been  reported.  Appar- 
ently, the  critical  temperature  of  ruminants  is  rather  low, 
while  the  "  work  of  digestion  "  is  the  source  of  a  relatively 
large  amount  of  heat,  so  that,  under  ordinary  conditions  of  feed- 
ing, these  animals  are  producing  a  surplus  of  heat  and  therefore 
a  ration  supplying  net  energy  sufficient  for  maintenance  is  also 
ample  as  a  source  of  heat. 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  108  (1908),  pp.  84-86. 


CHAPTER  IX 

MAINTENANCE    (Continued) —THE    REQUIREMENTS   OF 
MATTER 

As  was  pointed  out  in  the  introduction  to  the  previous  Chap- 
ter (361),  the  maintenance  requirement  is  a  twofold  one,  calling 
for  the  presence  in  the  feed  of  adequate  amounts  of  certain 
specific  substances  as  well  as  for  an  adequate  supply  of  energy. 
The  former  phase  of  maintenance  in  some  of  its  broader  aspects 
forms  the  subject  of  the  present  Chapter.  These  specific  sub- 
stances may  be  grouped  for  the  purpose  of  this  discussion  as 
proteins  or  their  constituents,  ash  ingredients  and  accessory 
constituents. 


§  i.  THE  PROTEIN  REQUIREMENTS  FOR  MAINTENANCE 

398.  Nature  of  protein  requirement.  —  As  was  shown  in 
Chapter  VII  (340),  the  loss  of  protein  which  the  fasting  body 
suffers  may  be  interpreted  in  two  ways.  First,  it  may  be  re- 
garded as  due  to  the  complete  breaking  down  of  a  certain  amount 
of  protein  as ,  the  necessary  accompaniment  of  cell  activity 
(Rubner's  "  wear  and  tear  "  quota).  Second,  it  may  be  sup- 
posed that  certain  atomic  groupings  contained  in  the  protein 
molecule  may  be  indispensable  for  the  normal  functioning  of 
the  body,  so  that,  if  they  are  not  contained  in  the  feed,  body 
protein  may  be  katabolized  for  the  sake  of  obtaining  them. 

In  either  case,  it  is  clear  that  what  the  feed  must  supply  in 
order  to  maintain  the  body  in  nitrogen  equilibrium  is  not, 
strictly  speaking,  protein  as  such,  but  materials  whose  digestive 
cleavage  will  yield  certain  amounts  and  proportions  of  the  con- 
stituent amino  acids.  On  the  first  hypothesis,  the  requirements 
for  the  different  "  building  stones  "  would  be  determined  sub- 
stantially by  the  quantities  of  each  existing  in  the  body  tissues 

313 


3 14  NUTRITION  OF   FARM  ANIMALS 

katabolized.  According  to  the  second  hypothesis,  it  might 
be  presumed  that  only  certain  of  the  atomic  groups  contained 
in  protein,  such  as  tryptophan,  e.g.,  would  need  to  be  supplied. 
Moreover,  it  appears  not  unlikely  that  both  hypotheses  may 
be  true  and  that  body  protein  is  katabolized  both  as  a  whole 
and  at  times  as  a  means  of  obtaining  certain  amino  acids.  If 
such  is  the  case,  substantially  all  the  "  building  stones  "  of  the 
proteins,  so  far  as  they  cannot  be  manufactured  in  the  body, 
must  be  supplied  in  the  feed,  but  relatively  more  of  certain 
particular  ones  might  be  required  than  would  be  indicated  by 
the  make-up  of  the  body  proteins.  Finally,  it  seems  to  be  fairly 
well  established  that  at  least  some  of  the  amino  acids  can  be 
manufactured  in  the  body.  This  is  almost  certainly  true  of 
glycin  and  perhaps  of  prolin  and  arginin.  If  such  be  the 
case,  it  becomes  even  more  clear  that  the  protein  requirement, 
so  called,  is  really  an  amino  acid  requirement. 

399.  Amino  acids  required  for  maintenance.  —  Our  actual 
knowledge  of  the  amino  acid  requirement  for  maintenance  is 
still  meager,  but  it  has  been  shown  that  a  supply  of  tryptophan 
and  probably  of  tyrosin  is  necessary  for  the  maintenance  of 
nitrogen  equilibrium,  while  lysin  is  dispensable. 

Willcock  and  Hopkins, 1  for  example,  found  that  the  zein  of 
maize,  which  contains  neither  tryptophan  nor  lysin,  was  capable  of 
supporting  neither  growth  nor  maintenance  in  mice,  while  the  addi- 
tion of  tryptophan  diminished  although  it  did  not  altogether  stop 
the  loss  of  nitrogen  from,  the  body.  Henriques  2  obtained  similar 
although  less  striking  results  in  experiments  with  rats.  It  is  to  the 
work  of  Osborne  and  Mendel 3  that  we  owe  the  most  conclusive  demon- 
stration of  the  necessity  of  tryptophan  for  maintenance.  They 
showed  conclusively  that  zein  as  the  sole  source  of  protein  was  in- 
capable of  maintaining  rats,  while  with  the  addition  of  tryptophan 
much  better  results  were  obtained  and  in  two  cases  complete  main- 
tenance for  a  long  time  was  secured.  Miss  Wheeler  4  has  reported 
similar  results  on  mice.  Furthermore,  Osborne  and  Mendel  have  shown 
that  the  deficiencies  of  zein  may  be  compensated  for  by  the  addition 
to  the  ration  of  other  proteins  containing  the  lacking  amino  acids. 

1  Jour.  Physiol.  (London),  35  (1906),  88. 

2  Ztschr.  Physiol.  Chem.,  60  (1909),  108. 

3  Carnegie  Institution  of  Washington,  Publication  No.  156  (1911);   Jour.  Biol. 
Chem.,  13  (1912),  233;  17  (1914),  325. 

4  Jour.  Exp.  Zoology,  15  (1913),  209. 


MAINTENANCE  —  REQUIREMENTS  OF   MATTER      315 

On  the  other  hand,  they  have  also  shown  that  lysin  is  not  essential  to 
protein  maintenance,  they  having  been  able  to  maintain  animals  for 
long  periods  on  rations  containing  as  their  sole  protein  gliadin,  which 
contains  no  lysin  but  does  contain  tryptophan. 

What  has  been  shown  regarding  the  necessity  of  tryptophan 
and  the  dispensability  of  lysin  for  maintenance  may  doubtless 
prove  to  be  true  for  other  protein  constituents,  so  that  ulti- 
mately it  may  be  possible  to  estimate  the  relative  maintenance 
values  of  proteins  on  the  basis  of  their  chemical  constitution. 
At  present,  however,  this  is  far  from  being  the  case.  The 
constitution  of  many  of  the  proteins,  particularly  those  of  the 
roughages,  is  known  inadequately  or  not  at  all,  while  the  specific 
amino  acid  requirements  for  maintenance  have  still  to  be  worked 
out  and  may  conceivably  vary  as  between  different  species. 

400.  Relative  values  of  proteins  for  maintenance.  —  The 
facts  regarding  the  variations  in  the  constitution  of  the  different 
proteins  which  are  recorded  in  Chapter  I  (50)  render  it  evident 
that  these  substances  may  be  of  quite  unequal  value  as  sources 
of  amino  acids  to  the  organism.  Thus,  according  to  the  data 
there  tabulated,  gliadin  and  zein  would  be  about  three  or  four 
times  as  valuable  as  legumin  as  a  source  of  the  amino  acid 
prolin,  while  on  the  other  hand  legumin  would  be  2 \  times  as 
valuable  as  wheat  glutenin  as  a  source  of  lysin.  The  cereal 
proteins,  especially  those  of  wheat,  are  notably  rich  in  glutamic 
acid  and  therefore  relatively  poorer  in  other  constituents.  If, 
then,  the  protein  requirement  for  maintenance  is  in  reality  an 
amino  acid  requirement  it  would  seem  that  these  various  pro- 
teins must  be  of  unequal  value  for  that  purpose. 

As  regards  single  proteins,  the  experimental  evidence  just 
cited  strongly  supports  this  presumption,  while  Osborne  and 
Mendel l  have  likewise  shown  the  existence  of  distinct  differences 
in  the  values  of  lactalbumin,  casein  edestin,  gliadin  and  milk 
proteins  for  the  maintenance  of  rats.  It  must  not  be  forgotten, 
however,  that  both  man  and  domestic  animals  ordinarily  con- 
sume a  mixture  of  proteins,  so  that  it  may  be  presumed  that 
deficiencies  or  excesses  of  particular  "  building  stones  "  com- 
pensate for  each  other  to  a  greater  or  less  extent.  On  the  whole 
the  statement  seems  justified  that  while  distinct  differences 

1  Jour.  Biol.  Chem.,  2Z  (1915),  241. 


316  NUTRITION  OF  FARM  ANIMALS 

between  mixed  proteins  from  different  sources  as  regards  their 
value  for  maintenance  have  been  shown  to  exist,  they  appear 
in  many  cases  to  be  less  than  might  be  anticipated  from  the 
known  differences  in  their  chemical  constitution.  As  a  matter 
of  practical  necessity,  then,  pending  the  further  investigations 
so  greatly  to  be  desired,  the  only  course  open  for  the  present 
seems  to  be  to  follow  established  custom  and  deal  with  the  pro- 
tein of  feeding  stuffs  and  rations  as  a  whole,  with  the  conscious- 
ness that  it  is  of  unequal  nutritive  value  in  different  materials 
but  in  the  belief  that  such  differences  are  not  in  all  probability 
so  great  as  to  seriously  invalidate  the  general  usefulness  of  the 
results. 

Influence  of  feed  supply  on  protein  katabolism 

401.  The  minimum  of  feed  protein.  —  The  physiological 
minimum  (339)  below  which  the  protein  katabolism  of  the 
fasting  animal  cannot  be  reduced  evidently  constitutes  a  lower 
limit  to  the  necessary  supply  of  feed  protein,  but  what  surplus, 
if  any,  above  this  minimum  must  be  supplied  in  order  to  secure 
actual  protein  maintenance  is  still  an  unsettled  question.  That 
the  amount  of  feed  protein  necessary  for  maintenance  is  rel- 
atively small  has  been  fully  demonstrated.  It  appears  to  be 
well  established  also  that  on  a  diet  containing  an  abundance 
of  non-nitrogenous  nutrients,  especially  of  carbohydrates,  a 
supply  of  protein  materially  less  than  the  protein  katabolism 
during  complete  fasting  is  sufficient  to  meet  the  needs  of  the 
organism,  while  it  is  possible  that  an  amount  little  or  no  greater 
than  that  katabolized  when  abundance  of  carbohydrates  is 
consumed  will  suffice. 

Fats  appear  to  be  distinctly  less  efficient  than  carbohydrates  in 
keeping  the  protein  katabolism  at  the  minimum.  Precisely  why  this 
is  the  case  has  not  been  fully  made  out,  although  Landergren  l  has 
advanced  the  explanation  that  a  minimum  of  carbohydrates  is  essen- 
tial to  the  chemical  processes  of  metabolism  and  that  when  a  sufficient 
amount  is  not  supplied  in  the  feed,  protein  is  katabolized  for  the  sake 
of  producing  carbohydrates,  with  the  result  that  on  a  low  protein 
diet  nitrogen  katabolism  is  increased. 

1  Jahresber.  Tier.  Chem.,  32  (1903),  685. 


MAINTENANCE  —  REQUIREMENTS  OF  MATTER       317 


The  facts  recorded  in  Chapter  VII  (335-338),  however,  make 
it  evident  that  the  protein  katabolism  may  be  affected  by  the 
amount  of  both  protein  and  non-nitrogenous  material  available 
in  the  body.  For  a  correct  interpretation  of  the  results  of  ex- 
periments upon  the  maintenance  requirement  of  protein,  there- 
fore, a  knowledge  of  the  influence  of  the  feed  supply  upon  the 
protein  katabolism  is  essential. 

402.  Surplus  protein  katabolized.  —  While  a  relatively  small 
quantity  of  digestible  protein  is  sufficient,  in  the  presence  of  an 
abundant  supply  of  fuel  material,  to  maintain  the  body  in 
nitrogen  equilibrium,  an  increase  of  the  feed  protein  above 
this  minimum  does  not  result  in  any  large  or  long-continued 
gain  of  protein  tissue  by  the  mature  animal,  but  simply  in- 
creases the  protein  katabolism,  as  is  shown  by  the  prompt 
appearance  of  a  corresponding  amount  of  nitrogen  in  the  urine. 

TABLE  57.  —  PROTEIN  KATABOLISM  OF  SHEEP  PER  DAY  AND  HEAD 


SHE 

EP  I 

SHE! 

,p  II 

Nitrogen 
digested 

Nitrogen 
in  urine 

Nitrogen 
digested 

Nitrogen 
in  urine 

Grams 

Grams 

Grams 

Grams 

Period  i     

8.18 

7.48 

7.8l 

6.98 

Period  2    

17.86 

16.82 

17.72 

16.37 

Period  3    

27.22 

25-75 

27-33 

23-94 

Period  4                              ... 

36.00 

32.71 

37.07 

32.00 

Period  5     

26.76 

25-63 

26.91 

24-54 

Period  6    

17.62 

16.64 

16.94 

J5-99 

Period  7     

8-34 

,       8.06 

8.00 

7.62 

The  fact  was  demonstrated  more  than  fifty  years  ago  by  C.  Voit 
in  collaboration  at  first  with  Bischoff  1  and  later  alone  and  with  Pet- 
tenkofer  2  in  experiments  on  carnivorous  animals,  and  almost  innu- 
merable subsequent  investigations  have  shown  that  it  is  true  not 
only  of  these  animals  but  of  man  and  of  herbivorous  animals  as  well. 

Of  the  -numerous  investigations  on  herbivora  in  which  the  nitro- 

1  Gesetze  der  Ernahrung  des  Fleischfressers,  1860. 

2  Published  chiefly  in  the  Annalen  der  Chemie  und  Pharmacie  and  the  Zeitschrift 
fur  Biologic.     See  also  Voit,  "Physiologic  des  Stoffwechsels,"  in  Hermann's  Hand- 
buch  der  Physiologic. 


318  NUTRITION  OF  FARM  ANIMALS 

gen  excretion  has  been  determined,  Table  57  may  serve  as  an  ex- 
ample.1 Two  sheep  were  fed  in  periods  i  and  7  a  basal  ration  of 
hay  and  barley  meal.  To  this  ration  were  added  in  the  intermediate 
periods  varying  amounts  of  nearly  pure  protein  in  the  form  of  con- 
glutin  (of  lupins)  or  of  flesh  meal.  A  comparison  of  the  nitrogen 
digested  from  the  ration  with  the  urinary  nitrogen  shows  that  the 
latter  increased  and  diminished  substantially  parallel  with  the  former. 

403.  Utilization  of  protein  limited.  —  That  the  mere  consump- 
tion of  protein  cannot  cause  a  large  storing  up  of  it  is  indeed 
sufficiently   obvious   from   daily   experience.     The   muscles   of 
the  weakling  cannot  be  converted  into  those  of  the  athlete  by 
feeding  him  upon  a  meat  diet,  nor  the  small  man  increased  in 
size  by  a  very  abundant  protein  supply.     The  protein  tissues 
of  the  mature  animal  have  reached  their  natural  limit  of  size 
and  consequently  the  capacity  of  the  body  to  store  up  protein 
is  limited.     Beyond  the  minimum  required  to  make  good  the 
necessary  katabolism  in  the  cells,  protein  can  be  utilized  in 
such  an  animal  only  to  a  small  extent  as  protein,  and  it  is  there- 
fore rapidly  katabolized,  its  nitrogen  appearing  in  the  urine  as 
urea  and  other  familiar  end  products.     Nor  is  the  situation 
essentially    different    in    the   growing   or    the    milk-producing 
animal.     While    these    animals    are    able    to    utilize    consid- 
erable amounts  of  feed  protein,  yet  the  limit  to  this  utilization 
is  set  by  the  normal  rate  of  growth  of  the  protein  tissues  or 
the    capacity   of   the   mammary   glands   to  manufacture   the 
casein  and  other  proteins  of  the  milk.     Any  surplus  of  pro- 
tein over  what  can  be  used  for  this  purpose  is  katabolized 
precisely  as  is  a  surplus  over  the  very  small  demand  of  the 
unproductive  mature  animal.      (Compare  Chapter  XI,  §  2  and 
Chapter  XIII,  §4.) 

404.  Protein  as  a  source  of  energy.  —  This  increased  katab- 
olism of  protein,  however,  is  not  to  be  regarded  as  the  total 
loss  of  so  much  feed  material.     In  the  presence  of  a  surplus  of 
protein,   the  amino  acids  resulting  from  its  digestion  are  in 
large   part   deaminized    (233),    their   nitrogen   being   excreted 
chiefly  as  urea,  while  a  non-nitrogenous  residue  is  left  which 
contains  the  larger  portion  of  the  chemical  energy  of  the  protein 
which  it  represents  and  is  in  condition  to  be  oxidized  as  fuel 

1  Henneberg  and  Pfeiffer;  Jour.  Landw.,  38  (1890),  215. 


MAINTENANCE  —  REQUIREMENTS   OF   MATTER      319 

material  (229).  The  increased  nitrogen  excretion  on  a  high 
protein  diet  is  simply  the  method  by  which  the  organism  gets 
rid  of  surplus  nitrogen  while  retaining  the  larger  share  of  the 
energy  of  the  protein  for  fuel  purposes.  It  does  not  mean  the 
total  destruction  of  the  corresponding  amount  of  protein,  but 
simply  its  transformation  into  compounds  which  can  serve  as 
sources  of  energy. 

405.  Fluctuations  of  body  protein.  —  Although  in  the  mature 
animal  a  surplus  of  feed  protein  is  largely  katabolized,  so  that 
a  continued  increase  of  the  protein  tissue  of  the  animal  cannot 
be  brought  about,  as  can  that  of  the  adipose  tissue,  simply  by 
a  surplus  in  the  feed,  the  protein  content  of  such  an  animal  is 
not  to  be  regarded  as  absolutely  fixed,  so  that  the  protein  supply 
has  no  effect  upon  it.     On  the  contrary,  a  considerable  range  of 
variation  is  possible. 

Thus  it  is  a  familiar  fact  that  a  fasting  animal  may  live  and 
continue  to  perform  the  essential  bodily  functions  for  some 
time  while  losing  daily  a  not  inconsiderable  amount  of  protein. 
To  cite  a  single  striking  example,  Rubner  observed  in  a  fasting 
rabbit  up  to  the  time  of  death,  on  the  nineteenth  day,  a  loss  of 
45.2  per  cent  of  the  computed  nitrogen  of  the  body.  While 
this  is  an  extreme  instance,  nevertheless  it  is  evident  that  there 
must  be  a  relatively  large  loss  of  body  protein  in  those  more  mod- 
erate cases  in  which  the  deprivation  of  protein  is  not  continued  so 
long  as  to  cause  death.  Furthermore,  the  losses  occurring  in 
these  latter  cases  may  be  made  good  by  subsequent  feeding 
and  the  animal  restored  to  its  original  state.  Illustrations  of 
the  same  fact  are  familiar  in  the  human  subject  in  the  emacia- 
tion due  to  illness  and  the  restoration  of  the  body  during  con- 
valescence. In  brief,  it  is  evident  that  the  body  of  the  mature 
animal  may  fluctuate  within  somewhat  wide  limits  as  regards 
its  protein  content  without  necessarily  causing  any  serious  or 
permanent  derangement  of  its  functions. 

406.  Storage   of  feed  protein.  —  Similar,  although   smaller, 
fluctuations  in  the  protein  content  of  the  body  appear  to  be 
caused  by  variations  in  the  supply  of  feed  protein,  an  increase 
in  the  latter  giving  rise  to  more  or  less  storage  of  nitrogenous 
matter  in  the  body,  while  a  decrease  has  a  contrary  effect. 

In  other  words,  as  regards  its  stock  of  nitrogenous  materials 
the  organism  may  exist  and  function  at  a  higher  or  lower  level 


320  NUTRITION  OF  FARM   ANIMALS 

according  to  the  amount  of  protein  supplied  in  the  feed,  while 
for  each  level  of  protein  stock  a  certain  supply  in  the  feed  is 
necessary  —  that  is,  the  protein  requirement  for  maintenance 
varies.  With  carnivora  on  a  largely  protein  diet  the  adjust- 
ment, of  the  body  to  the  protein  supply  seems  to  take  place 
rather  promptly.  In  the  case  of  herbivora,  however,  the  ad- 
justment appears  to  be  more  gradual,  possibly  owing  to  the 
relatively  large  supply  of  non-nitrogenous  ingredients  in  their 
feed,  and  apparently  some  gain  of  protein  may  continue  for  a 
considerable  time,  although  when  expressed  as  a  percentage  of 
either  the  total  feed  protein  or  of  the  body  protein  the  gain  is 
relatively  small. 

407.  Effect  of  deficiency  of  non-nitrogenous  nutrients. — 
The  prime  demand  of  the  organism  is  for  energy  for  the  per- 
formance of  its  vital  functions,  and  if  necessary  it  will  draw 
upon  its  own  tissues  for  this  purpose.  No  clear  conception  of 
the  laws  of  protein  metabolism  can  be  reached  without  taking 
into  consideration  the  energy  relations. 

As  has  already  been  shown,  the  proteins  or  at  least  the  cleavage 
products  of  their  digestion  readily  undergo  a  process  of  deam- 
inization  by  which  their  nitrogen  is  split  off  and  excreted,  leaving 
a  non-nitrogenous  residue  which  is  available  as  a  source  of 
energy.  Ordinarily,  however,  the  proportion  of  energy  derived 
from  the  katabolism  of  protein  is  relatively  small,  the  non- 
nitrogenous  nutrients  constituting  its  principal  source. 

But  if,  with  an  amount  of  protein  in  the  feed  just  sufficient 
to  sustain  nitrogen  equilibrium,  the  non-nitrogenous  nutrients, 
especially  the  carbohydrates,  be  so  reduced  in  amount  that 
the  total  energy  supply  is  insufficient  for  maintenance,  not 
only  is  body  fat  drawn  upon  to  make  up  the  deficit,  but  the 
protein  katabolism  also  increases,  so  that  a  supply  of  this 
nutrient  which  was  previously  adequate  became  insufficient 
and  a  loss  of  body  protein  occurs. 

The  effect  is  naturally  most  marked  when  the  non-nitrogenous 
nutrients  are  withdrawn  altogether.  For  example,  Voit  and  Korku- 
noff 1  found  that  when  a  dog  was  given  an  abundant  supply  of  carbohy- 
drates, protein  equivalent  to  about  4.5  grams  of  nitrogen  was  sufficient 
to  maintain  him  in  nitrogen  equilibrium.  But  when  a  similar  amount 

1  Ztschr.  Biol.,  32  (1895),  67. 


MAINTENANCE  —  REQUIREMENTS   OF   MATTER      321 

of  protein  was  given  without  non-nitrogenous  nutrients  it  proved 
entirely  insufficient  for  this  purpose  and  about  three  times  as  much 
was  required  to  attain  protein  maintenance,  as  the  following  table 
shows :  — 

TABLE  58.  —  EFFECT  OF  PROTEIN  SUPPLY  ON  PROTEIN  KATABOLISM  OF 

DOG 


NITROGEN  IN  — 


FEED 

Feed 

Feces  and 
urine 

Gain  (+)  or 
loss  (-) 

Grams 

Grams 

Grams 

Nothing   

0 

3.996 

-  3.996 

Extracted  meat  (grams)  : 

100    

4.10 

5o58 

-  1.458 

140  

c.74 

6.40^ 

_       jce 

6  77 

7  217 

—     .447 

185  

7-59 

7.804 

-     .214 

200    

8.20 

8.726 

-     .526 

230    

10.24 

10-579 

-     -339 

360    

11.99 

12.052 

—     .062 

4IO 

15  58 

14.314 

+  1.266 

360  

13.68 

13.622 

+     -058 

The  results  furnish  also  a  striking  illustration  of  the  interesting  rela- 
tions between  protein  supply  and  protein  katabolism  which  had  been 
demonstrated  more  than  30  years  earlier  by  the  classic  experiments 
of  Bischoff  and  Voit  (402),  while  rendering  it  evident  that  the  quantity 
of  protein  required  to  produce  nitrogen  equilibrium  when  fed  alone  is 
very  far  from  representing  the  minimum  demand  of  the  body. 

What  is  so  strikingly  true  in  the  total  absence  of  non-nitrog- 
enous nutrients  holds  good  also  in  less  degree  in  case  of  their 
relative  deficiency.  If  a  portion  of  the  non-nitrogenous  nu- 
trients are  withdrawn  from  a  mixed  ration,  the  protein  katab- 
olism usually  increases. 

408.  Effect  of  surplus  of  non-nitrogenous  nutrients.  —  If, 
on  the  contrary,  non-nitrogenous  nutrients  be  added  to  a 
ration,  they  tend  to  diminish  the  katabolism  of  protein. 

As  regards  rations  deficient  in  energy,  this  is,  of  course,  only 
the  converse  of  the  statement  of  the  preceding  paragraph  that 


322 


NUTRITION  OF  FARM  ANIMALS 


the  withdrawal  of  these  materials  tends  to  increase  the  protein 
katabolism,  and  as  regards  maintenance  or  submaintenance 
rations  the  two  statements  are  equivalent.  But  even  in  the 
case  of  supermaintenance  rations  it  has  been  found  that  the 
addition  of  a  surplus  of  fat  or,  in  particular,  of  carbohydrates, 
to  a  ration  containing  more  than  the  minimum  of  protein  tends 
to  reduce  the  protein  katabolism  to  a  lower  level.  The  effect 
is  well  illustrated,  for  example,  by  those  of  Kellner's  respiration 
experiments  on  cattle  1  in  which  starch  was  added  to  basal 
rations  which  were  themselves  sufficient  to  cause  some  fattening. 
The  following  table  compares  the  urinary  nitrogen  upon  the 
basal  ration  with  that  upon  the  augmented  ration :  — 

TABLE  59.  —  EFFECT  OF  STARCH  ON  PROTEIN  KATABOLISM  OF  CATTLE 


DAILY  URINARY  NITROGEN 

On  basal 
ration 

With  addition 
of  starch 

Ox  D 

Grams 
122.54 
106.03 
86.30 
109.28 
122.62 

Grams 
104.69 
81.18 

63.83 

81.71 
103.13 

Ox  F     . 

Ox  G     

OxH 

Ox  T 

It  has  likewise  been  shown  that  this  effect  is  produced  not 
only  by  the  true  fats  and  by  the  soluble  hexose  carbohydrates, 
such  as  starch  and  the  sugars,  but  likewise  by  the  pentoses  and, 
in  the  case  of  herbivorous  animals,  by  those  ill-known  ingredients 
of  feeding  stuffs,  especially  of  the  crude  fiber  and  the  nitrogen- 
free  extract,  which  disappear  in  the  passage  of  the  feed  through 
the  alimentary  canal  and  which  are  commonly  spoken  of  as 
being  digested.  This  statement  covers  also  the  organic  acids, 
whether  resulting  from  -the  fermentation  of  the  carbohydrates 
or  contained  in  the  feed. 

409.  Protein  katabolism  depends  chiefly  on  supply.  —  It 
should  be  clearly  understood  that  even  in  the  presence  of  a 
surplus  of  fat  or  carbohydrates  the  dependence  of  the  protein 

1  Landw.  Vers.  Stat.,  53  (1900). 


MAINTENANCE  —  REQUIREMENTS  OF  MATTER       323 

katabolism  upon  the  protein  supply  still  holds  true.  Even 
the  most  liberal  supply  of  non-nitrogenous  nutrients  cannot 
prevent  the  splitting-off  and  excretion  of  the  nitrogen  of  surplus 
protein  which  was  illustrated  in  previous  paragraphs,  but  simply 
reduces  it  somewhat  below  the  level  which  it  would  otherwise 
reach.  To  that  extent,  it  helps  to  bring  about,  and  probably 
to  prolong  somewhat,  the  temporary  storage  of  protein  men- 
tioned on  a  previous  page  (406)  and  thus  to  bring  the  animal 
upon  a  higher  plane  of  protein  nutrition. 

It  is  clear  from  the  foregoing  statements  that  no  sharp  dis- 
tinction is  to  be  conceived  of  between  an  insufficiency  and  a 
sufficiency  of  non-nitrogenous  nutrients,  but  rather  a  tendency 
on  the  part  of  the  latter  to  diminish  the  protein  katabolism,  a 
tendency  more  or  less  marked  according  to  their  abundance  in 
the  ration.  It  is  not  to  be  understood  that  no  nitrogenous 
material  is  katabolized  for  fuel  purposes  as  long  as  sufficient 
non-nitrogenous  nutrients  are  present  to  supply  the  demands 
for  energy,  nor  that  even  the  largest  quantities  of  the  latter 
can  prevent  the  katabolism  of  protein  supplied  in  excess  of  its 
possible  constructive  use  by  the  body. 

Protein  requirements  of  farm  animals 

410.  Minimum  and  optimum  of  protein.  —  In  considering  the 
protein  requirements  of  the  different  species  of  farm  animals, 
it  is  important  to  distinguish  between  two  points  of  view.  On 
the  one  hand,  it  may  be  sought  to  determine  the  least  amount 
of  feed  protein  upon  which  the  protein  tissues  of  the  animal  can 
be  maintained.  On  the  other  hand,  the  endeavor  may  be  to 
formulate  the  most  advantageous  amount  of  protein  to  supply 
when  an  animal  is  actually  to  be  maintained  for  a  time  and  this 
amount  may  very  possibly  be  greater  than  the  physiological 
minimum.  The  first  point  of  view,  however,  is  plainly  the 
fundamental  one  and  should  first  receive  consideration.  Hav- 
ing determined  the  lower  limit  of  protein  supply,  it  will  then 
be  possible  to  consider  intelligently  the  advantages,  if  any,  of 
a  surplus. 

In.  considering  the  results  of  experiments  directed  toward  the 
determination  of  the  minimum  of  feed  protein  required  by  any 
individual  or  species,  it  is  essential  to  bear  in  mind  the  facts 


324  NUTRITION  OF   FARM  ANIMALS 

regarding  the  influence  of  the  feed  supply  upon  the  protein 
katabolism  which  have  just  been  considered. 

411.  The  plane  of  protein  nutrition.  —  It  has  been  shown 
in  previous  paragraphs  that  the  protein  katabolism  adjusts 
itself  more  or  less  promptly  to  the  supply  in  the  feed.     A  surplus 
above  the  minimum  requirement,  while  causing  a  small  storage 
of  protein,  results  chiefly  in  raising  the  plane  of  protein  nutrition 
and  so  increasing  the  katabolism  until  income  and  outgo  of 
nitrogen    come    into   equilibrium.     The   mere  fact,   therefore, 
that  an  animal  is  in  equilibrium  with  a  certain  supply  of  protein 
in  its  feed  by  no  means  proves  the  latter  to  be  the  least  amount 
necessary  for  the  maintenance  of  the  animal,  since  it  may  be 
living  upon  an  unnecessarily  high  plane  of  protein  nutrition. 

412.  The    supply    of    non-nitrogenous   nutrients.  —  It   has 
also  been  shown  that  the  sufficiency  of  a  given  amount  of  pro- 
tein depends  not  only  upon  the  plane  of  protein  nutrition  of 
the  body,  but  also,  within  certain  limits,  upon  the  amount  of 
non-nitrogenous    nutrients    supplied   with  the  protein.     With 
an  abundant  supply  of  the  former  an  amount  of  protein  equal  to 
the  fasting  katabolism,  or  perhaps  even  less,  appears  to  be  a 
sufficient  minimum  for  maintenance.     As  the  supply  of  non- 
nitrogenous  materials  is  reduced  a  larger  supply  of  feed  protein 
seems  to  be  required  to  reach  equilibrium  because  more  and 
more  of  it  is  diverted  for  use  as  fuel,  so  that  in  the  total  absence 
of  non-nitrogenous   nutrients  a  large    excess  of  protein  must 
be  fed  before  equilibrium  between  income  and  outgo  of  nitro- 
gen is  reached.     In  interpreting  experiments  or  formulating  a 
maintenance  ration,  therefore,  it  is  not  sufficient  to  consider 
simply  the  amount  of  protein,  but  account  must  also  be  taken  of 
the  supply  of  non-nitrogenous    materials,  and   only  when  the 
net  energy  content  of  the  ration  is  ample  for  maintenance  can 
it  be  concluded  that  a  loss  of  body  protein  shows  the  protein 
supply  to  be  insufficient. 

413.  Value  of  non-protein.  —  The  crude  protein  of  the  feed 
of  farm  animals  includes  not  only  true  protein  but  a  great 
variety   of   other    nitrogenous    substances,   grouped   for   con- 
venience under   the  designation  non-protein.     In  considering 
the  results  of  experiments  upon  the  protein  requirements  of 
these  animals,  therefore,  it  is  necessary  to  determine  whether 
the  true  protein  should  be  the  basis  of  comparison  or  whether 


MAINTENANCE  —  REQUIREMENTS   OF   MATTER      325 

the  non-protein  has  some  value  for  maintaining  the  protein 
tissues  of  the  body. 

It  appears  to  have  been  demonstrated  by  recent  experimental 
results,  especially  by  those  of  Kellner,  Morgen,  and  the  Labora- 
tory for  Agricultural  Research  in  Copenhagen,  that  the  non- 
protein  of  ordinary  feeding  stuffs  is  available  for  the  maintenance 
of  ruminants,  probably  indirectly  through  a  conversion  to 
protein  by  means  of  micro-organisms  in  the  digestive  tract 
(141).  On  the  other  hand,  investigations  have  thus  far  failed 
to  demonstrate  that  non-protein  has  any  material  value  for 
other  species  or  for  production  purposes  (786-789).  In  the 
computation  of  rations  for  productive  feeding,  therefore,  it 
appears  desirable  for  the  present  to  consider  ordinarily  only 
the  digestible  true  protein,  ignoring  the  non-protein.  This 
implies,  however,  that  the  results  of  experiments  upon  the 
protein  requirement  shall  be  expressed  in  the  same  manner. 

This  will  have  two  effects :  First,  it  will  make  the  protein  require- 
ment appear  smaller  than  it  really  is.  Suppose,  for  example,  that 
a  series  of  trials  in  which  the  ratio  of  digestible  non-protein  to 
digestible  protein  is  i :  10  shows  that  nitrogen  equilibrium  is  reached 
with  a  ration  supplying  500  grams  protein  and  50  grams  non- 
protein.  Regarding  the  true  protein  only,  the  maintenance  require- 
ment is  500  grams,  while  including  the  non-protein  it  is  550  grams. 

In  the  second  place,  however,  this  error  will  be  largely  compen- 
sated for  when  the  actual  computation  of  rations  is  also  based  on  the 
true  protein.  Thus  in  the  case  just  supposed,  if  a  maintenance  ration 
be  computed  from  any  feed  or  mixture  in  which  the  ratio  of  non- 
protein  to  protein  is  the  same  as  in  the  experiments  from  which  the 
maintenance  was  deduced,  viz.,  i  :  10,  it  is  obvious  that  the  same  final 
result  will  be  reached  whether  the  maintenance  requirement  be  con- 
sidered to  be  500  grams  of  true  protein  or  550  grams  of  crude  protein. 
Only  when  the  proportion  of  non-protein  to  true  protein  varies  widely 
from  that  existing  in  the  rations  used  in  determining  the  protein  re- 
quirement will  any  significant  error  arise  in  computing  rations. 

In  the  results  considered  on  succeeding  pages,  both  the  crude 
protein  and  true  protein  of  the  rations  are  stated  when  these 
are  given  in  the  reports  of  the  experiments. 

414.  Computation  to  unit  weight.  —  It  was  shown  in  Chap- 
ter VII  (345)  that  the  energy  requirement  for  maintenance  is 
substantially  proportional  to  the  body  surface  of  the  animal. 


326  NUTRITION  OF  FARM  ANIMALS 

No  similar  comparisons  of  the  protein  requirement  appear  to 
have  been  made.  Since,  however,  the  minimum  protein  re- 
quirement does  not  represent  a  demand  for  energy  but  for 
certain  specific  substances  required  for  the  normal  functioning 
of  the  body,  it  seems  plausible  to  suppose  that  its  amount  will 
depend  rather  upon  the  mass  of  active  tissue  than  upon  the  body 
surface.  If  such  be  the  case,  the  protein  requirement  may, 
with  sufficient  accuracy  for  practical  purposes,  be  computed  in 
proportion  to  the  live  weight  and  that  course  is  followed  in 
the  succeeding  paragraphs. 

415.  Protein  requirement  of  cattle.  —  For  obvious  reasons 
it  is  impracticable  to  ascertain  the  fasting  katabolism  of  rumi- 
nants as  a  basis  for  estimating  their  maintenance  requirement 
as  regards  protein,  but  by  a  comparison  of  the  recorded  experi- 
ments in  which  the  nitrogen  balance  upon  small  amounts  of  feed 
has  been  determined  it  is  possible  to  fix  approximately  the  limit 
of  protein  supply  below  which,  even  in  the  presence  of  an  abun- 
dant supply  of  non-nitrogenous  nutrients,  a  loss  of  body  protein 
occurs^. 

Of  the  investigations  upon  the  energy  requirement  for  main- 
tenance summarized  in  Chapter  VIII  (381)  only  those  of  Kellner 
and  the  live  weight  experiments  of  the  writer,  together  with 
the  early  results  of  Henneberg  and  Stohmann,  afford  data 
regarding  the  minimum  protein  requirement.  While  protein 
maintenance  was  probably  secured  in  the  remaining  instances 
there  is  no  sufficient  evidence  to  show  that  a  surplus  of  protein 
was  not  being  consumed  (402,  411).  In  addition  to  the  foregoing, 
the  investigations  by  the  Laboratory  for  Agricultural  Research 
in  Copenhagen  l  upon  the  protein  requirements  for  milk  pro- 
duction (586)  also  afford  approximate  data  as  to  the  main- 
tenance requirement,  and  Fingerling,2  in  experiments  upon  the 
protein  requirements  of  growing  calves  (471),  obtained  inter- 
esting indications  regarding  the  quantity  required  for  main- 
tenance. 

The  lowest  recorded  amounts  per  1000  pounds  live  weight 
upon  which  nitrogen  equilibrium  was  reached  were  0.21  pound 

1  Denmark-Beretning  fra  den  Kgl.  Veterinaer  of  Landbohojskoles  Laboratorium 
for  landokonomiske  Forsog.  6ode,  1906,  and  63de,  1907,  Kobenhavn.  Translated 
by  Mallevre,  Societe  de  1' Alimentation  Rationelle  du  Betail.  Compte  Rendu  de 
neme  et  i2eme  Congres. 

2Landw.  Vers.  Stat.,  76  (1911),  i. 


MAINTENANCE  —  REQUIREMENTS   OF   MATTER      327 


and  0.25  pound  of  crude  protein  in  experiments  on  dry  cows, 
while  in  experiments  on  steers  almost  as  small  a  quantity,  viz., 
0.27  pound  crude  protein  or  0.23  pound  true  protein,  fell  very 
little  short  of  maintaining  the  nitrogen  balance.  Aside  from 
these  somewhat  exceptional  results,  the  lowest  figures  obtained 
were  0.43  pound  crude  protein  and  0.38  pound  true  protein. 
If  the  few  exceptionally  low  figures  be  omitted,  the  average  and 
range  of  the  results  of  the  other  experiments  are  as  follows :  — 

TABLE  60.  —  AVERAGE  AND  RANGE  or  PROTEIN  REQUIREMENT  OF  CATTLE 


NUMBER 
OF  EXPERI- 
MENTS 

PROTEIN  REQUIREMENT 

Average 
Pound 

Maximum 
Pound 

Minimum 
Pound 

Crude  protein     
True  protein 

IQ 

12 

°-55 
0.52 

0-75 
0.63 

0-43 
0.38 

It  seems  safe,  therefore,  to  estimate  0.6  pound  of  crude  pro- 
tein or  0.5  pound  true  protein  per  1000  pounds  live  weight  as 
representing  in  a  general  way  the  minimum  protein  require- 
ment of  cattle,  with  a  range  of  perhaps  o.i  or  0.2  pound  either 
way  under  varying  conditions. 

416.  Protein  requirement  of  sheep.  —  While  a  considerable 
number  of  experiments  with  sheep  are  on  record  in  which  live 
weight  maintenance  was  secured,  and  a  smaller  number  in  which 
the  nitrogen  balance  was  maintained,  few  of  them  afford  satis- 
factory data  as  to  the  minimum  protein  requirement. 

A  distinct  difference  between  cattle  and  sheep,  which  affects  the 
protein  requirement,  lies  in  the  greater  demand  for  protein  incident 
to  the  growth  of  wool  in  the  latter  animals  as  compared  with  that  of 
hair  in  the  former.  Determinations  by  Armsby  and  Fries  on  the 
same  two  steers  in  two  consecutive  winters  showed  an  average  pro- 
duction of  epidermal  tissue,  including  the  growth  of  hair  and  the  loss 
in  brushings,  equivalent  to  0.0025  lb.  protein  per  day  and  1000 
pounds  live  weight,  an  amount  too  small  to  materially  affect  the  main- 
tenance requirement.  In  the  case  of  sheep,  determinations  by  several 
investigators  have  shown  the  daily  growth  of  wool  per  1000  pounds 
live  weight  to  contain  from  o.io  to  0.15  lb.  of  protein,  the  average 
being  0.135  lb.  Although,  as  these  figures  show,  the  protein  re- 


328  NUTRITION  OF   FARM   ANIMALS 

quirement  of  sheep  for  the  growth  of  wool  is  considerably  greater  than 
that  of  cattle  for  the  growth  of  hair,  the  absolute  difference,  after  all, 
does  not  add  very  greatly  to  the  total  maintenance  requirement. 

The  current  feeding  standards  for  the  maintenance  of  sheep  call 
for  i. 0-1.6  Ib.  of  digestible  crude  protein  per  1000  pounds  live 
weight,  apparently  upon  the  basis  of  Henneberg  and  Stohmann's  early 
experiments  (382)  in  which  1.3  Ib.  of  crude  protein  or  i.o4lb.  true 
protein  produced  but  a  slight  gain  of  body  protein  in  addition  to  the 
growth  of  the  wool.  There  can  be  little  doubt,  however,  that  Henne- 
berg and  Stohmann's  sheep  received  a  surplus  of  protein  above  the 
actual  maintenance  requirement. 

In  a  series  of  20  digestion  and  metabolism  experiments  by  Schulze 
and  Marcker,1  decidedly  smaller  amounts  of  protein  proved  sufficient 
to  maintain  nitrogen  equilibrium,  the  average  of  6  experiments  in 
which  no  loss  of  body  protein  was  observed  being  0.653  Ib.  digest- 
ible crude  protein  per  1000  pounds  live  weight.  It  is  evident,  then, 
that  the  protein  supply  of  sheep  can  be  reduced  much  below  the 
amount  fed  in  Henneberg  and  Stohmann's  experiments  without  lead- 
ing to  a  loss  of  body  protein. 

The  most  satisfactory  data  regarding  the  minimum  require- 
ment of  sheep  are  afforded  by  Katayama's2  investigations,  in 
which  increasing  amounts  of  nearly  pure  protein  ("  aleuronat  ") 
were  added  to  a  basal  ration  very  poor  in  protein,  consisting  of 
hay,  oat  straw,  starch  and  cane  sugar.  The  protein  in  every  case 
was  substituted  for  a  corresponding  amount  of  starch,  so  that 
the  total  energy  of  the  ration  remained  substantially  unchanged. 
On  the  average  of  two  animals,  0.41  Ib.  digestible  true  protein 
per  1000  pounds  live  weight  was  sufficient  to  maintain  the 
nitrogen  balance.  Since,  however,  the  growth  of  wool  must 
have  gone  on,  with  a  corresponding  storage  of  nitrogen,  there 
must  have  been  an  equivalent  loss  of  protein  by  the  active 
tissues  of  the  body. 

If  to  the  minimum  of  0.41  pound  there  be  added  0.14  Ib. 
per  1000  pounds  live  weight  for  the  growth  of  wool,  it  appears 
that  the  minimum  protein  requirement  for  the  maintenance  of 
mature  sheep  is  in  the  neighborhood  of  0.55  Ib.  It  is  inter- 
esting to  note  that  the  actual  maintenance  requirement  for 
the  body  tissues  is  apparently  quite  as  low  relatively  as  for 
cattle. 

1  Wolff ;  Die  Ernahrung  der  landwirtschaftlichen  Nutetiere,  p.  300, 

2  Landw.  Vers.  Stat.,  69  (1908),  321. 


MAINTENANCE  —  REQUIREMENTS  OF   MATTER      329 


417.  Protein  requirement  of  swine.  —The  determinations 
of  the  fasting  katabolism  of  swine  recorded  in  Chapter  VIII 
(377)  gave  an  average  of  0.48  Ib.  per  thousand  pounds  live 
weight  for  the  fasting  protein  katabolism  of  swine,  although 
with  a  considerable  range  in  the  individual  results.  McCollum  1 
has  reported  considerably  lower  figures  for  the  protein  katab- 
olism of  swine  receiving  no  protein  but  fed  liberal  amounts  of 
starch,  the  mean  of  twelve  experiments  being  0.26  Ib.  per 
1000  pounds  live  weight  with  a  range  of  0.14  Ib. -0.33  Ib. 
Whether,  however,  such  small  amounts  as  these  are  sufficient 
for  actual  maintenance,  or  if  not,  what  excess  above  them  is 
necessary,  has  not  been  certainly  determined. 

In  the  experiments  of  Von  d.  Heide  and  Klein  (378),  in  one  of 
which  an  approximate  maintenance  ration  was  fed  to  three  young 
swine,  there  was  a  material  gain  of  protein  by  the  animals.  The 
amounts  actually  katabolized,  however,  as  shown  by  the  amount  of  ni- 
trogen excreted  in  the  urine,  were  as  follows  for  the  three  animals 
together :  — 


PROTEIN  KATABOLISM 

WEIGHT 

Per  Head 

Per  1000  Lb. 
Live  Weight 

Kgs. 

Grams 

Lb. 

Period  I  Maintenance     

228.1 

152.4 

0.67 

Period  II  Fattening    '. 

246.5 

156.2 

0.63 

Period  III  Fattening  |       261.5 

I5I-3 

0.58 

Dietrich, 2  in  his  experiments  upon  maintenance  ration  of  swine 
(378), found  that  0.70  to  0.84  Ib.  of  digestible  protein  per  thousand 
pounds  live  weight  sufficed  to  produce  nitrogen  equilibrium  in  two 
periods  following  an  eight-day  fasting  period,  but  that  about  the  same 
amounts  (0.80  to  0.90)  previous  to  the  fasting  period  were  insufficient, 
while  in  two  trials  in  which  respectively  0.94  and  1.06  Ib.  were  con- 
sumed protein  maintenance  was  reached. 

418.  Protein  requirement  of  the  horse.  — In  the  experiments 
by  Grandeau  and  LeClerc  described  in  Chapter  VIII  (386  d), 

1  Wis.  Expt.  Sta.,  Research  Bui.  21. 

2  Ills.  Expt.  Sta.,  Bui.  163  (1913)- 


330 


NUTRITION  OF   FARM   ANIMALS 


the  nitrogen  balance  of  the  horses  was  determined  during  six 
of  the  periods.  The  following  table  shows  the  amounts  of 
protein  and  of  non-protein  nitrogen  digested  in  each  period, 
the  urinary  nitrogen,  and  the  small  losses  in  epithelial  tissue 
(epidermis,  hoofs,  hair,  etc.) :  — 

TABLE  61.  —  NITROGEN  BALANCE  OF  HORSES 


HORSE  No.  i 

HORSE  No.  2 

HORSE  No.  3 

January, 
1884 

April, 
1884 

Novem- 
ber, 1883 

Mav, 
i88~4 

December, 
1883 

March, 
1884 

Digested  : 
Protein  nitrogen  . 
Non-protein 
nitrogen  .     . 
Total  nitrogen 

Nitrogen  of  epithe- 
lial tissue 
Urinary  nitrogen     . 
Nitrogen  gained 

Grams 
43-19 

1.  20 

Grams 
34-29 

—    I.OI 

Grams 
38.94 

~    3-23 

Grams 
34-22 

10.78 

Grams 
41.82 

-    2.09 

Grams 
24.72 

-    4-58 

44-39 

33-28 

35-71 

35-00 

39-73 

20.14 

1.46 

35-17 
7.76 

1.46 

38.75 

-  6-93 

1.46 
30.70 
3-55 

1.46 
41.92 
1.62 

1.46 
37.62 
0.65 

1.46 

32.70 
—  14.02 

Omitting  the  results  upon  horse  No.  3  in  March,  when  the 
digestible  protein  was  exceptionally  low,  the  other  five  periods 
show  an  average  daily  gain  of  nitrogen  of  1.33  grams,  while 
the  average  crude  protein  digested  was  235  grams,  or  0.59 
Ib.  per  1000  pounds  live  weight,  equivalent  to  about  0.50  Ib. 
true  protein. 

419.  The  optimum  of  protein.  —  The  data  of  the  foregoing  para- 
graphs seem  to  indicate  a  striking  uniformity  in  the  minimum 
protein  requirement  of  the  principal  species  of  domestic  animals 
with  perhaps  the  exception  of  the  hog  when  mature,  0.4  to  0.6 
Ib.  per  1000  pounds  live  weight  apparently  sufficing  to  main- 
tain nitrogen  equilibrium  under  favorable  conditions. 

It  should  be  clearly  understood,  however,  that  this  figure 
represents  a  more  or  less  accurately  determined  limit.  It  pur- 
ports to  be  the  amount  below  which  the  protein  supply  can- 
not be  reduced  without  eventual  protein  starvation.  The 
animal  body,  however,  may  adjust  itself  to  a  wide  range  of 
protein  supply  above  the  minimum,  using  some  of  it  to  increase 


MAINTENANCE  — REQUIREMENTS  OF  MATTER       331 

the  stock  of  protein  in  the  body  and  katabolizing  the  remainder 
as  fuel  material.  An  increase  of  the  protein  supply  above  the 
minimum  causes,  after  a  relatively  short  time,  the  main- 
tenance of  the  body  protein  at  a  higher  level  (411).  The  prac- 
tical question  in  actual  maintenance  is  far  less  as  to  the  least 
amount  of  protein  which  may  be  used  than  as  to  the  most 
advantageous  level  of  protein  nutrition;  that  is,  as  to  the 
optimum  of  protein. 

This  question  has  been  warmly  debated  in  connection  with 
human  nutrition,  having  been  brought  to  the  fore  especially 
by  the  investigations  of  Chittenden  and  his  associates.1 

On  the  whole  it  cannot  be  said  that  a  considerable  surplus 
of  protein  over  the  minimum  requirement  for  maintenance  — 
that  is,  the  maintenance  of  protein  nutrition  on  a  high  plane 
-has  been  proved  to  be  of  any  material  advantage  in  the 
maintenance  either  of  men  or  of  domestic  animals  during 
periods  covering  several  months.  Whether  a  continued  low 
protein  diet  through  years  or  generations  would  show  a  different 
result  is  at  present  largely  a  matter  of  speculation.  It  is  to  be 
remarked,  however,  that  the  particular  point  under  discussion 
is  the  protein  requirement  of  the  mature  organism.  That  a 
deficiency  of  protein  in  the  diet  of  a  growing  animal  may  have 
disastrous  results  is  clear.  If,  however,  the  habitual  food  supply 
of  a  race  of  men  or  a  group  of  animals  is  low  in  protein,  the 
young  are  likely  to  share  this  deficiency  with  the  mature,  and 
it  seems  not  impossible  that  this  is  an  important  factor  in  the 
alleged  physical  inferiority  of  certain  races  of  men  living  on  a 
low  protein  diet.  This  consideration  warns  us  to  exercise  care 
in  this  respect  in  the  management  of  the  breeding  herd. 

420.  Digestibility  of  low  protein  rations.  —  In  the  actual 
maintenance  feeding  of  farm  animals,  the  matter  of  the  digest- 
ibility of  the  ration  must  also  be  considered.  It  has  been 
shown  (723,  724)  that  a  relative  deficiency  of  protein  in  the 
ration  tends  to  depress  the  apparent  digestibility  of  both  the 
protein  and  non-nitrogenous  nutrients,  especially  in  the  case  of 
ruminants.  A  maintenance  ration  for  these  animals  containing 
the  minimum  amount  of  protein  together  with  the  quantity 
of  non-nitrogenous  nutrients  required  to  maintain  the  energy 
supply,  would  have  a  nutritive  ratio  (709) ,  computed  in  the  ordi- 

1  Physiological  Economy  in  Nutrition. 


332  NUTRITION  OF   FARM  ANIMALS 

nary  way,  of  approximately  i :  12.  On  such  a  ration  there 
would,  in  all  probability,  be  some  loss  of  digestibility  and  an  in- 
crease of  its  protein  by  50  per  cent  might  perhaps  effect  a  gain  in 
digestibility  which  would  more  than  offset  the  increased  cost, 
if  any.  Indeed,  unless  feeding  stuffs  especially  poor  in  protein 
are  used,  it  may  often  be  difficult,  even  were  it  desirable,  to 
reduce  the  protein  content  of  a  maintenance  ration  to  the  low 
level  of  absolute  necessity. 


§  2.  THE  ASH  REQUIREMENTS  FOR  MAINTENANCE 

421.  Ash   ingredients   indispensable.  —  That   a    supply   of 
the  so-called  mineral  or  ash  ingredients,  as  well  as  of  protein 
and  of  energy  yielding  materials,  is  necessary  for  the  growth  and 
maintenance  of  animals  has  been  fully  recognized  since  the 
time  of  Liebig,  and  was  strikingly  demonstrated  by  the  well- 
known  experiments  of  Forster  1  and  of  Lunin,2  which  showed 
that  animals  supplied  only  with  ash-free  feed  perished  even 
sooner  than  when  deprived  of  all  feed. 

Some  of  the  reasons  for  these  facts  were  indicated  in  the  dis- 
cussion of  the  functions  of  the  nutrients  in  Chapter  V  (268-272), 
where  it  was  shown  that,  besides  their  structural  importance 
for  both  the  skeleton  and  the  soft  tissues,  the  presence  of  ash 
ingredients  in  the  body  fluids  is  essential  to  the  maintenance 
and  regulation  of  the  vital  processes.  Aside  from  the  specific 
uses  of  single  elements,  such  as  iron,  fluorin,  iodin,  etc.,  three 
general  functions  of  the  ash  ingredients  as  a  whole  were  there 
mentioned,  viz.,  the  maintenance  in  the  body  fluids  and  tissues 
of  the  normal  osmotic  pressure  and  of  the  relative  concen- 
tration of  the  various  ions,  and,  as  a  specific  case  of  the  latter, 
the  preservation  of  neutrality. 

422.  Ash  content  of  feed  large.  —  Most  feeding  stuffs,  how- 
ever, and  particularly  the  mixed  rations  of  farm  animals,  con- 
tain what  appear  at  first  sight  to  be  much  larger  amounts  of 
ash  ingredients  than  the  body  requires.     Milk  production,  for 
example,   causes  an   exceptionally  large  drain  upon   the  ash 
content  of  the  body,  yet  even  rations  made  up  of  materials 
relatively  poor  in  ash  contain  much  larger  amounts  than  are 

1  Ztschr.  Biol.,  9  (1873),  297.  a  Ztschr.  Physiol.  Chem.,  5  (1881),  31. 


MAINTENANCE  —  REQUIREMENTS  OF   MATTER       333 


found  in  the  milk  produced.  Zuntz  l  gives  the  following  com- 
parison of  the  ash  ingredients  in  a  ration  recommended  by 
Kellner  for  a  cow  producing  22  pounds  of  milk  daily  with  the 
ash  content  of  the  milk  yield :  - 

TABLE  62.  —  COMPARISON  OF  ASH  CONTENT  OF  RATION  AND  OF  MILK 


CaO 

MgO 

K2O 

Na20 

P2O6 

Cl 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

In  ration 

88  Ib.  wet  distiller's  grain    . 

12 

24 

1  2O 

20 

52 

8 

5.5  Ib.  meadow  hay    .     .     . 

17 

8 

43 

2 

9 

I? 

8.8  Ib.  straw       

IO 

3 

30 

3 

8 

5 

4.4  Ib.  dried  potatoes       .     . 

2 

4 

45 

i 

9 

3 

i.i  Ib.  wheat  bran       .     .     . 

7 

3 

6 

0.2 

ii 

0-5 

2.2  Ib.  sesame  cake     .     .     . 

25 

13 

H 

4 

32 

i 

73 

55 

258 

30.2 

121 

34-5 

In  22  Ib.  milk  ...     .     .     .     . 

17 

2 

17 

4 

20 

IO 

Comparisons  like  the  foregoing  have  tended  to  confirm  the 
somewhat  prevalent  idea  that  rations  adequate  in  other  re- 
spects may  be  assumed  to  contain  a  sufficiency  of  ash  ingredients. 
This  is  doubtless  true  of  animals  living  in  a  state  of  nature  but 
it  is  a  questionable  assumption  under  the  artificial  conditions 
to  which  many  farm  animals  are  subjected,  as  when  receiving 
an  excess  of  some  single  grain  like  Indian  corn  or  of  technical 
by-products,  or  when  stimulated  to  a  high  degree  of  produc- 
tion. 

423.  Ash  ingredients  digestible.  —  It  is  true  that  of  this  rela- 
tively large  supply  of  mineral  matter  in  ordinary  rations,  a  very 
considerable  fraction,  especially  of  certain  elements,  is  found 
in  the  feces,  and  this  fact  has  led  to  their  being  regarded  as 
relatively  indigestible.  As  was  stated  in  Chapters  III  and 
IV  (164,  199),  however,  this  apparently  low  digestibility  arises 
from  the  fact  that  the  intestinal  tract  constitutes  the  normal 
path  of  excretion  for  certain  elements,  notably,  in  the  case  of 
herbivora,  for  calcium  and  phosphorus.  Thus  Forster  has 
shown  that  in  the  dog  the  calcium  of  the  feed  is  largely  resorbed 

1  Jahrb.  Deut.  Landw.  Gesell.,  1912,  p  570. 


334  NUTRITION  OF  FARM  ANIMALS 

in  the  upper  part  of  the  intestine  where  the  contents  are  acid, 
while  more  or  less  of  it  is  excreted  again  in  the  lower  intestine. 
While  it  is  impossible,  therefore,  to  determine  by  means  of  the 
ordinary  digestion  experiment  how  much  of  such  ingredients 
have  actually  been  resorbed  and  excreted  again  and  what 
proportion  has  escaped  digestion,  it  appears  safe  to  conclude 
that  at  least  a  considerable  share  of  them  has  been  dissolved  and 
resorbed  in  the  upper  digestive  tract  and  that  the  insufficiency 
of  certain  rations  as  regards  mineral  ingredients  is  not  due  to 
the  indigestibility  of  the  latter. 

424.  Contrast  between  organic  and  inorganic  nutrients.  — 
There  is  an  obvious  distinction  between  organic  and  inorganic 
nutrients.  The  former  may  be  said  to  be  destroyed  in  the 
performance  of  their  functions.  A  molecule  of  dextrose  or  of 
stearin,  for  example,  can  yield  energy  to  the  body  only  by  being 
split  up  and  oxidized  step  by  step  to  carbon  dioxid  and  water. 
The  case  is  similar  with  protein  so  far  as  it  is  used  for  fuel  pur- 
poses and  even  its  specific  functions  seem  to  involve  the  cleavage 
and  oxidation  of  its  molecules.  With  the  electrolytes  contained 
in  the  body  the  case  is  different.  A  molecule  of  disodium 
phosphate,  for  example  (or  its  ions),  is  not  destroyed  by  the 
performance  of  its  functions  in  maintaining  neutrality  no  matter 
how  long  it  serves  that  purpose  and  the  molecule  of  sodium 
chlorid  contributes  its  quota  to  the  osmotic  pressure  of  the 
blood  serum  as  long  as  it  remains  dissolved  in  that  fluid.  Only 
as  it  escapes  from  the  body  will  the  need  for  a  fresh  supply 
arise. 


Losses  of  ash 

425.  Causes  of  loss.  —  So  far,  therefore,  as  the  maintenance 
of  mature  animals  is  concerned,  the  magnitude  of  the  ash  re- 
quirement will  be  substantially  determined  by  the  rate  at 
which  the  various  elements  are  eliminated  from  the  body 
through  the  excretory  organs.  In  growing  animals  there  is  in 
addition,  of  course,  the  demand  for  ash  ingredients  for  structural 
purposes,  both  for  the  building  up  of  the  skeleton  and  to  a  less 
degree  of  the  soft  tissues,  but  even  in  this  case  the  total  ash 
requirement  is  determined  in  large  degree  by  the  rate  of  ex- 
cretion. 


MAINTENANCE  —  REQUIREMENTS  OF   MATTER      335 

Some  of  the  more  important  factors  leading  to  the  excretion 
of  ash  ingredients  from  the  body  and  hence  to  the  depletion  of 
its  stock  are  considered  in  the  following  paragraphs :  - 

426.  Maintenance  of  osmotic  pressure.  —  In  the  discussion 
of  excretion  in  Chapter  IV  it  was  stated.  (198)  that  the  essential 
function  of  the  kidneys  is  to  maintain  a  constant  composition 
of  the  blood,  those  organs  acting  somewhat  like  an  overflow 
valve  by  means  of  which  any  excess  of  a  substance  above  the 
normal  limit  begins  to  be  excreted.     In  this  way  the  osmotic 
pressure  in  the  body  is  regulated  and  an  excess  of  any  salt  in 
the  feed,  sodium  chlorid  for  example,  is  disposed  of. 

The  matter  is  not  quite  so  simple,  however,  as  would  appear 
from  the  foregoing  statement.  The  action  of  the  kidneys  in 
eliminating  surplus  salts  and  so  preventing  an  increase  of  osmotic 
pressure  is  not  confined  to  the  particular  salt  supplied  in  excess, 
but  extends  to  others  also.  This  is  most  strikingly  shown  in 
the  case  of  the  alkalies.  If,  for  example,  unusual  amounts 
of  potassium  salts  are  consumed,  an  increased  excretion  of 
this  element  results  in  the  urine,  but  the  need  of  keeping 
the  osmotic  pressure  at  its  normal  level  seems  to  be  so  great 
that  more  or  less  of  the  sodium  salts  are  also  excreted,  even 
though  their  concentration  in  the  blood  may  not  be  above  the 
normal. 

This  relation  as  regards  potassium  and  sodium  has  been 
shown  by  the  well-known  investigations  of  Bunge,1  who  holds 
that  the  desire  for  common  salt  on  the  part  of  herbivora  is  due 
to  the  presence  of  relatively  large  amounts  of  potassium  in 
their  feed  and  the  consequent  tendency  towards  impoverish- 
ment of  the  body  as  regards  sodium.  The  occurrence  of  salt 
hunger  in  animals  receiving  feed  with  an  abnormal  ratio  of 
potassium  to  sodium  has  been  explained  in  the  same  way. 

In  other  words,  the  effort  of  the  body  to  maintain  the  osmotic 
pressure  of  its  fluids  by  removing  a  surplus  of  some  one  ingre- 
dient may  bring  about  an  impoverishment  as  regards  other 
elements  and  so  create  a  need  for  an  increased  supply  of  the 
latter  in  the  feed. 

427.  Maintenance  of  neutrality.  —  Attention  was  called  in 
Chapter  V  (271)  to  the  fact  that  practical  neutrality  of  the 
blood  serum  and  lymph  is  necessary  for  the  normal  functioning 

1  Physiologic  des  Menschen,  1905. 


336  NUTRITION  OF  FARM   ANIMALS 

of  the  body  cells  and  to  the  important  part  played  by  the  ash 
ingredients  in  maintaining  this  neutrality. 

a.  Acidosis.  —  A  variety  of  chemical  processes,  both  normal 
and  pathological,  occur  in  the  body  which  tend  to  disturb  its 
neutrality  either  by  the  addition  of  acid  or  the  giving  off  of 
alkali  so  as  to  produce  the  condition  known  as  acidosis,  by 
which  is  meant  a  relative  excess  of  acid  over  basic  radicles. 

A  well-known  example  of  pathological  acidosis  is  that  observed  in 
diabetes.  The  perverted  metabolism  of  this  disease  results  in  the 
production  of  large  amounts  of  oxybutyric  acid  (266),  which  is  neu- 
tralized to  a  certain  extent  by  means  of  ammonia  derived  from  the 
katabolism  of  protein  but  whose  gradual  accumulation  finally  results 
in  the  diabetic  coma.  Another  example  is  the  form  of  infantile  aci- 
dosis in  which  an  excess  of  fat  in  the  food  results  in  the  formation  of 
insoluble  calcium  salts  of  the  fatty  acids  in  the  intestines  and  so  re- 
moves basic  ingredients  in  the  feces.  It  has  been  suggested  that  the 
failure  of  young  animals  to  thrive  on  milk  exceptionally  rich  in  fat 
may  be  due  in  part  to  the  same  cause. 

Several  sources  of  acid  exist  in  the  normal  organism. 

First,  acids  may  be  consumed  as  such,  either  in  natural 
products  or  in  fermented  materials  like  silage.  These  acids 
are  neutralized  by  the  alkalies  of  the  saliva  or  of  the  pancreatic 
juice,  which  are  thus  temporarily  withdrawn  from  the  body 
fluids.  After  resorption,  however,  the  resulting  alkali  salts  of 
the  more  common  acids  are  readily  oxidized,  yielding  carbon 
dioxid  and  water  and  restoring  to  the  body  fluids  the  bases 
previously  withdrawn.  Small  amounts  of  some  acids,  such  as 
tartaric  and  malic,  however,  tend  to  escape  oxidization  and  to  be 
excreted  in  the  urine,  carrying  a  corresponding  amount  of  base 
with  them.  Oxalic  acid  and  its  salts  are  oxidized  with  difficulty 
and  tend  to  impoverish  the  body  in  calcium  by  the  formation 
of  the  insoluble  calcium  oxalate.  This  acid  is  liable  to  be  es- 
pecially injurious  to  horses  and  swine  and  to  young  ruminants, 
while  in  mature  ruminants  it  seems  to  be  largely  destroyed  by 
fermentation  in  the  first  stomach. 

Second,  the  fermentations  in  the  paunch  of  ruminants  are  a 
source  of  large  amounts  of  organic  acids  which,  like  those  con- 
tained in  the  feed,  may  cause  a  temporary  withdrawal  from  the 
body  fluids  of  alkali  which  is  later  restored  when  the  salts  are 
katabolized. 


MAINTENANCE  —  REQUIREMENTS  OF  MATTER      337 

Third,  the  considerable  amount  of  hippuric  acid  produced 
by  herbivora  makes  a  very  considerable  draft  upon  the  organism 
for  bases.  Thus,  in  four  experiments  by  Diakow  cited  by 
Zuntz,  it  was  equivalent  to  from  J  to  f  of  the  total  excess  of 
bases  over  inorganic  acids  in  the  urine. 

Fourth,  in  the  katabolism  of  the  proteins,  nucleo-proteins 
and  other  compounds  containing  sulphur  and  phosphorus, 
these  elements  are  largely  oxidized  to  sulphuric  and  phosphoric 
acids.  The  sulphur  of  one  pound  of  protein  having  the  com- 
position of  serum  albumin,  for  example,  if  fully  oxidized,  would 
yield  the  equivalent  of  nearly  one  ounce  by  weight  of  con- 
centrated sulphuric  acid.  High  protein  rations,  therefore, 
tend  to  bring  about  a  loss  of  bases  from  the  body. 

b.  Neutralization  of  acids.  —  In  all  these  various  ways  there 
is  a  constant  tendency  to  disturb  the  neutrality  of  the  body 
fluids  and  towards  the  establishment  of  an  acidosis,  to  prevent 
which  the  acids  must  be  neutralized.  The  significance  of 
this  was  first  shown  by  the  experiments  of  Lunin  already  re- 
ferred to  (421),  which  showed  that  the  life  of  animals  fed  on 
ash-free  feed  could  be  considerably  prolonged  by  the  addition 
of  sodium  carbonate  to  neutralize  the  acids  produced  in  the 
body.  Normally,  this  neutralization  is  accomplished  in  two 
general  ways. 

First,  an  excess  of  acid  may  be  combined  with  the  ammonia 
which  is  produced  from  the  amino  acids  in  the  katabolism  of 
protein  (233)  and  is  subsequently  converted  into  urea  in  the 
liver.  A  part  of  this  ammonia,  however,  may  be  diverted 
from  this  course  and  utilized  to  neutralize  acids,  the  resulting 
ammonium  salts  being  excreted  in  the  urine  in  place  of  a  cor- 
responding amount  of  urea.  The  ammonia  arising  from  the 
putrefactions  in  the  lower  intestines  (140)  may  serve  the  same 
purpose.  A  small  quantity  of  ammonium  salts,  arising  from  the 
neutralization  of  the  acids  produced  especially  in  the  protein 
katabolism,  is  normally  found  in  the  urine,  while  the  feeding 
of  inorganic  acids  or  their  injection  into  the  blood  stream,  or  a 
pathological  acidosis,  may  greatly  increase  their  amount. ; 

On  the  basis  of  early  experiments  upon  rabbits  it  has  been  taught 
that  the  ability  to  neutralize  acids  by  means  of  ammonia  is  peculiar 
to  carnivora  and  omnivora  and  is  present  to  a  very  limited  extent  in 
z 


338  NUTRITION  OF  FARM  ANIMALS 

herbivora.  It  seems  a  priori  unlikely  that  such  a  difference  in  the 
metabolic  processes  should  exist,  and  later  investigations  have  shown 
that  there  is  no  such  fundamental  distinction  between  the  various 
species.  It  should  be  remembered,  however,  that  the  protein  metab- 
olism of  herbivorous  animals  is  often  on  a  relatively  low  plane,  and 
that  consequently  relatively  less  ammonia  may  be  available  than  in 
the  case  of  carnivorous  animals. 

Another  phase  of  the  matter,  which  has  received  little  considera- 
tion, is  the  possibility  that  the  long-continued  presence  of  ammonium 
salts  in  the  body  may  have  an  injurious  effect.  The  possibility  of 
injury  through  acid  rations  in  this  way  could  hardly  be  determined 
except  by  means  of  experiments,  covering;  if  possible,  the  whole  life 
cycle  of  the  animal. 

Second,  an  excess  of  acid  may  be  disposed  of  by  combination 
with  the  fixed  bases  present  in  the  body.  These  are,  in  the 
first  instance,  those  contained  in  the  carbonates  and  phosphates 
of  the  blood  and  other  fluids.  Henderson,  as  already  noted, 
has  shown  that  these  salts  are  present  in  the  blood  serum  in 
such  proportions  that  relatively  large  amounts  of  acids  may  be 
disposed  of  in  this  way  without  materially  altering  the  reaction 
of  the  blood. 

c.  Excretion  of  acids.  —  The  neutralization  of  acids  produced 
in  the  body  does  not,  however,  necessarily  involve  the  excretion 
of  an  equivalent  amount  of  base.  It  is  a  familiar  fact  that  the 
urine  may  possess  a  considerable  degree  of  acidity.  The  work 
of  Henderson  shows  that  the  kidneys  are  able  to  separate  more 
or  less  of  the  phosphoric  acid  from  the  bases  of  the  blood,  ex- 
creting it  as  acid  phosphates  in  the  urine  and  retaining  a  cor- 
responding amount  of  bases  in  the  blood. 

428.  The  skeleton  as  a  reserve  of  ash  ingredients.  —  The 
store  of  bases  in  the  body  fluids,  however,  is  limited.  The  larger 
part  of  the  ash  of  the  body  is  contained  in  the  skeleton,  which 
constitutes  a  relatively  large  reserve  of  basic  phosphates  and 
carbonates  which  may  be  drawn  upon  to  supplement  the  supply 
in  the  blood.  This  fact  has  an  important  bearing  on  the  ques- 
tion of  the  necessary  ash  supply  in  the  feed,  while  it  must  likewise 
be  taken  into  account  in  experimental  work.  Long-continued 
maintenance  on  abnormal  feeds  or  under  conditions  favoring 
acid  production  in  the  body  may  result  in  extracting  from  the 
body  comparatively  large  amounts  of  mineral  matter  even  to 


MAINTENANCE  — REQUIREMENTS  OF  MATTER      339 

the  extent,  apparently,  of  bringing  about  pathological  condi- 
tions, while  on  the  other  hand,  normal  feeding  and  conditions 
may  enable  such  losses,  if  not  too  extensive,  to  be  made  good. 
The  point  which  is  of  special  importance  is  that  these  fluctua- 
tions of  the  ash  content  of  the  skeleton  affect  the  ash  as  a  whole. 
It  was  found  by  Aron  that  the  composition  of  the  bone  ash  as 
given  in  Chapter  II  (81)  remains  practically  constant  even  when 
the  skeleton  has  been  greatly  impoverished  in  total  ash.  In 
particular  this  has  been  shown  to  be  true  not  only  of  the  calcium 
and  phosphoric  acid  of  the  bones  but  also  of  the  minor  in- 
gredients such  as  carbonic  acid,  magnesium  and  even  sodium. 
A  draft  upon  the  skeleton  for  sodium,  for  example,  could  be 
met  only  by  the  mobilization  of  an  amount  of  total  bone  ash 
containing  the  requisite  quantity  of  sodium,  and  this  would  re- 
sult in  throwing  into  the  circulation  relatively  large  amounts 
of  calcium  and  phosphoric  acid  for  which  there  may  be  no  re- 
quirement, thus  raising  the  percentage  of  these  ingredients 
above  the  normal  limit  and  leading  to  their  excretion. 


Maintenance  of  ash  balance 

429.  Relation  to  feed.  —  The  foregoing  paragraphs  clearly 
indicate  that  the  ash  requirements  for  maintenance  depend 
chiefly  on  the  amounts  of  the  various  ash  ingredients  which, 
for   one  reason  or  another,  are  thrown  into    the   circulation 
in    excess  of    the   body's   needs   and   are   therefore   removed 
by   the   excretory  organs,  and  furthermore,  that  the  nature 
of  the  feed  consumed,  particularly   the   relative   proportions 
of  its  ash  elements,  is  an  important  factor  in  determining  these 
losses. 

430.  Deficiencies  in  ash  ingredients.  —  Some  feeding  stuffs 
contain  relatively  little  total  ash  and  are  especially  deficient 
in  particular  elements.     The  most  striking  and  familiar  example 
of  this  is  maize.     According  to  Henry  and  Morrison  1  average 
maize  contains  about  1.8  per  cent  of  total  ash,  while  its  lime  con- 
tent is  only  0.02  per  cent  and  that  of  soda  only  0.04  per  cent. 
Some  by-product  feeds  are  similarly  poor  in  particular  ingre- 
dients.   Obviously  such  feeds  are  not  by  themselves  well  adapted 

1  Feeds  and  Feeding,  i$th  Ed.,  p.  672. 


340  NUTRITION  OF  FARM   ANIMALS 

for  growing  or  milking  animals,  in  which  a  storage  of  ash  in  the 
product  occurs.  For  the  simple  maintenance  of  mature  an- 
imals, however,  which  is  the  topic  under  discussion,  the  question 
whether  the  small  amount  of  lime  present,  for  example,  is  ad- 
equate depends  upon  the  rate  at  which  lime  is  being  lost  from 
the  body.  If  this  loss  could  be  reduced  to  zero,  a  feeding  stuff 
containing  no  lime  whatever  would  seem  to  be  adequate  for 
maintenance  so  far  as  that  substance  is  concerned.  In  general, 
whether  a  feeding  stuff  or  ration  is  to  be  regarded  as  containing 
an  insufficient  amount  of  some  ash  element  for  maintenance  de- 
pends largely  on  how  it  affects  those  body  functions  which  de- 
termine the  rate  of  excretion  of  that  element. 

431.  Acid  and  basic  ash.  —  It  is  usually  considered  that  the 
most  important  relation  of  feed  in  the  respect  just  mentioned 
is  that  which  it  bears  to  the  maintenance  of  neutrality  in  the 
body  fluids.  Feeding  stuffs  or  rations  containing  in  assimilable 
form  much  sulphur  or  phosphorus,  for  example,  tend  to  cause 
the  production  in  the  body  of  corresponding  amounts  of  sul- 
phuric and  phosphoric  acids  which  must  be  neutralized.  On 
the  other  hand,  feeding  stuffs  containing  large  proportions  of 
the  bases  tend  to  have  the  opposite  effect.  The  relation  of  acid 
to  basic  elements  has,  therefore,  an  important  bearing  upon  the 
suitability  of  a  feeding  stuff  for  ash  maintenance.1 

Feeding  stuffs  differ  widely  in  this  respect.  In  general  it 
may  be  said  that  the  concentrates  contain  relatively  much 
phosphorus  and  sulphur,  little  calcium  and  only  moderate 
amounts  of  potassium  and  sodium,  while  the  roughages,  es- 
pecially those  of  better  quality,  are  rich  in  calcium  and  alkalies 
and  low  in  sulphur  and  phosphorus.  A  definite  measure  of 
these  differences  as  related  to  the  maintenance  of  neutrality  in 
the  body  is  obtained  by  converting  the  percentages  of  the 
several  ash  ingredients  into  chemical  equivalents. 

Alfalfa  hay,  for  example,  according  to  Henry  and  Morrison,2 
contains  in  one  kilogram  the  amounts  of  ash  ingredients  shown 
in  the  first  column  of  the  following  statement.  Dividing 

1  Evidently  the  sulphur  and  phosphorus  present  in  organic  combination  must  be 
included  in  such  comparisons  as  well  as  the  elements  present  in  the  form  of  electro- 
lytes.    In  the  older  ash  analyses  the  sulphuric  acid  represents  only  that  part  of  the 
sulphur  remaining  after  the  material  has  been  ashed,  which,  as  is  now  known,  is  but 
a  small  part  of  the  total  sulphur. 

2  Feeds  and  Feeding,  isth  Ed.,  p.  672. 


MAINTENANCE  —  REQUIREMENTS  OF  MATTER      341 

the  amount  of  each  by  its  equivalent  weight  gives  the  gram 
equivalents  shown  in  the  last  two  columns,  showing  that  a 
kilogram  of  this  feed  contains  1.300  gram  equivalents  of  excess 
base. 


ASH  INGRE- 
DIENTS 

EQUIVALENT 

GRAM  I 

EQUIVALENTS 

PER  KG. 

Acid 

Base 

K2O  .         ... 

Grms. 

22.\ 

04.  3 

O.473 

Na2O      .... 

5-6 

2 
62.1 

O.lSo 

CaO 

10  ^ 

2 

?6  i 

o  60^ 

MgO      .... 
Fe2O3     .... 

5-9 
i-7 

2 
40-36 
2 
I5Q.8 

0.2Q2 
0.064 

SO3 

7  8 

6 
80  06 

O  IQ^ 

PaOs1     .     .     .     . 
Cl 

5-4 

47 

2 
I42.O 
2 

0.076 

O    I  3  3 

0.404 

1.704 

The  results  of  a  considerable  number  of  computations  of  this 
sort  by  Forbes  2  are  contained  in  Table  X  of  the  Appendix,  the 
equivalents  of  bases  and  acids  being  expressed  in  cubic  centi- 
meters of  normal  solution.  The  table  shows  clearly  that  some 
feeding  stuffs,  like  the  hays,  for  example,  contain  a  considerable 
excess  of  basic  ingredients,  while  others  have  an  excess  of  acid- 
forming  elements.  The  ratio  of  phosphorus  to  calcium,  too, 
which  is  a,  special  case  of  the  ratio  of  acids  to  bases,  shows 
considerable  variations. 

432.  Significance  of  acidity  in  ash.  —  Much  stress  had  been 
laid  on  this  distinction  between  feeding  stuffs  with  acid  or 


1  Phosphoric  acid  is  regarded  as  neutralized  when  two  of  its  hydrogen  atoms  are 
replaced  by  basic  elements. 

2  Ohio  Expt.  Sta.,  Bui.  255. 


342  NUTRITION  OF   FARM  ANIMALS 

alkaline  ash  in  discussions  of  both  human  nutrition  and  that 
of  domestic  animals.  Doubtless  the  point  is  an  important  one 
but  the  assumption  that  all  excess  of  acid  over  basic  elements 
in  the  diet  should  be  avoided  seems  hardly  warranted,  especially 
as  regards  maintenance.  The  fact  that  the  body  is  to  a  certain 
extent  provided  with  a  means  of  defense  against  excessive  acids 
through  its  ability  to  neutralize  them  by  means  of  ammonia 
and  through  the  power  of  the  kidneys  to  separate  acids  and 
bases  is  sufficient  to  show  that  an  excess  of  acid-forming  ele- 
ments in  the  feed  is  not  necessarily  injurious.  It  is  only  when 
the  excess  is  so  large  as  to  exceed  the  capacity  of  these  regulative 
arrangements  and  when  it  therefore  begins  to  draw  on  the 
fixed  bases  of  the  body,  or  possibly  when  it  causes  the  produc- 
tion of  large  quantities  of  ammonia,  that  it  becomes  a  source  of 
danger. 

433.  Alkali  ratio  of  ash.  —  As  indicated  in  previous  para- 
graphs, the  ratio  of  potassium  to  sodium  in  a  feeding  stuff  may 
have  an  important  bearing  on  the  losses  of  ash  from  the  body. 
It  was  there  stated  that  while  a  surplus  of  potassium  salts  re- 
sorbed  into  the  blood  is  promptly  disposed  of  by  excretion 
through  the  kidneys,  it  may  carry  along  with  it  more  or  less 
sodium,  so  that  a  ration  relatively  rich  in  the  former  may  tend 
to  impoverish  the  body  in  the  latter.  Such  a  loss  of  sodium 
from  the  body,  it  would  appear,  might  have  serious  indirect 
effects  if  continued  long  enough  to  cause  a  draft  on  the  stock  of 
sodium  in  the  skeleton.  Such  a  draft,  as  already  said  (428), 
involves  the  solution  of  a  corresponding  amount  of  the  total 
ash  of  the  skeleton,  so  that  the  bones  would  be  impoverished 
in  other  ingredients,  especially  calcium  and  phosphoric  acid,  as 
well  as  sodium.  In  fact  it  has  been  found  that  fodders  that 
cause  malnutrition  of  the  bones  resulting  in  the  disease  known 
as  rickets  (Rachitis)  usually  show  a  misproportion  of  potassium 
to  sodium.  Zuntz  1  cites  the  following  comparisons  of  the  ash 
of  normal  hay  with  that  of  hays  causing  the  disease.  Along 
with  a  somewhat  greater  ratio  of  phosphoric  acid  to  calcium, 
the  injurious  hays  show  a  very  striking  difference  in  the 
alkali  ratio,  as  appears  from  the  following  table  to  which 
the  corresponding  figures  for  cow's  milk  have  been  added  for 
comparison :  — 

1  Jahrb.  Deut.  Landw.  Gesell.,  1912,  p.  577. 


MAINTENANCE  —  REQUIREMENTS  OF  MATTER       343 

TABLE  63 .  —  ALKALI  RATIO  OF  ASH 


K2O 

Na20 

RATIO 
Na20  TO 
K20 

Normal  Brandenburg  hay 

% 
20  oo 

% 

5    AT. 

i  : 

3  68 

Very  injurious  Brandenburg  hay  .  .  . 
Less  injurious  Brandenburg  hay  .  .  .  . 

Normal  Schwarzwald  hay  
Injurious  Schwarzwald  hay 

37-65 

33-54 
20.88 

37  4.O 

1.74 
2.50 

440 
O  21 

21.64 
13.42 

4-75 
178  10 

Cow's  milk  . 

34. 

8 

42  ? 

•zo 

434.  Balancing  of  ash  ingredients  in  the  ration.  —  While 
the  animal  body  has  a  considerable  degree  of  adaptability  to 
variations  in  the  ash  supply,  and  while,  during  short  periods, 
relatively  large  errors  in  this  respect  may  be  compensated  for 
out  of  the  comparatively  large  stock  of  ash  in  the  body,  never- 
theless, it  is  clear  from  previous  paragraphs  that  in  the  long 
run  a  reasonably  close  balance  of  the  ash  ingredients  in  the 
ration  is  necessary,  and  tables  like  that  of  the  Appendix  have 
been  computed  as  guides  for  this  purpose.  That  they  convey 
useful  information  cannot  be  denied,  but  any  attempt  to  base 
actual  estimates  regarding  ash  maintenance  or  the  ash  balance 
on  such  data  overlooks  some  important  considerations. 

Ash  not  entirely  digestible.  —  It  must  be  remembered  that  not 
all  of  the  ash  ingredients  of  the  feed  can  be  assumed  to  be  di- 
gested and  resorbed-.  It  is  true  that  much  of  the  ash  found  in 
the  feces  has  really  been  digested  and  excreted  again  in  the 
lower  intestines  but  this  is  by  no  means  true  of  the  entire  quan- 
tity. In  the  case  of  herbivora,  especially,  a  considerable  share 
of  the  dry  matter  of  the  feed  escapes  digestion  and  it  can  hardly 
be  doubted  that  it  carries  with  it  into  the  feces  more  or  less  of 
its  ash  elements.  This  is  particularly  true  of  the  sulphur  and 
phosphorus  of  the  proteins  and  the  nucleoproteins.  So  far  as 
these  escape  digestion,  they  carry  their  organic  sulphur  and 
phosphorus  with  them  into  the  feces  without  giving  it  oppor- 
tunity to  contribute  to  acid  production  in  the  body.  How  far 
the  same  thing  is  true  of  the  other  ash  elements  it  is  impossible 


344  NUTRITION  OF  FARM  ANIMALS 

to  say,  since  there  is  at  present  no  way  to  determine  how  much 
of  any  particular  ash  ingredient  found  in  the  feces  consists  of 
undigested  material  and  how  much  is  to  be  regarded  as  an  ex- 
cretory product.  This  being  the  case,  a  table  like  that  of  the 
Appendix  can  give  only  a  general  and  approximate  idea  of  the 
total  quantity  of  ash  or  of  the  balance  of  its  basic  and  acid 
elements  or  of  the  alkalies  in  the  materials  actually  resorbed 
and  entering  into  the  metabolism. 

Influence  of  supply  on  excretion.  —  Moreover,  it  is  necessary 
to  take  into  consideration  the  influence  discussed  in  previous 
paragraphs  (429-433)  of  the  nature  and  proportions  of  the  ash 
ingredients  actually  resorbed  upon  their  excretion.  For  ex- 
ample, potassium  may  lead  to  a  loss  of  sodium  and  this  in  turn 
to  losses  of  calcium  and  phosphoric  acid,  thus  possibly  affecting 
to  a  considerable  extent  the  ratio  of  acid  to  basic  elements  in 
the  excreta.  Adding  to  this  the  facts  that  more  or  less  of  the 
acids  produced  in  the  body  may  be  neutralized  by  ammonia 
instead  of  by  fixed  bases  (427  b),  and  that  the  kidneys  have  the 
power,  in  some  species  at  least,  to  separate  acids  from  bases 
(427  c),  leading  especially  to  excretion  of  acid  phosphates,  it 
is  evident  that  the  data  of  the  table  may  fall  considerably  short 
of  representing  the  actual  value  of  the  feed  as  regards  main- 
tenance of  the  ash  balance. 

435.  The  ash  balance.  —  These  considerations  render  it  evi- 
dent that  the  value  of  conclusions  as  to  the  balance  of  income 
and  outgo  of  ash  elements  drawn  from  the  composition  of  the 
feeding  stuffs  concerned  must  be  more  or  less  problematical, 
particularly  as  regards  farm  animals.  Such  conclusions  are 
more  or  less  probable  deductions  from  the  facts  outlined  in 
previous  paragraphs  regarding  the  functions  of  ash  in  the  body 
and  need  to  be  checked  by  direct  experiments.  The  actual 
effect  of  a  feeding  stuff  or  ration  on  the  ash  maintenance  of 
herbivora  can  be  determined  with  certainty  only  by  means  of 
direct  comparisons  of  the  income  and  outgo  of  all  the  ash  ele- 
ments, i.e.,  by  determinations  of  the  amounts  contained  in  feed, 
feces  and  urine  (metabolism  experiments)  or  by  comparative 
analyses  of  carefully  selected  test  and  control  animals  (com- 
parative slaughter  tests). 

Data  of  this  sort  for  mature  animals  are  very  scanty  but 
some  tentative  conclusions  may  be  drawn  from  experiments  by 


MAINTENANCE  —  REQUIREMENTS  OF  MATTER       345 

Diakow 1  and  Cochrane,2  each  on  a  single  steer.  Diakow's  ex- 
periments include  four  periods  on  mixed  rations  containing 
much  hay.  In  Cochrane's  experiments  alfalfa  hay  constituted 
the  sole  feed,  supermaintenance,  maintenance  and  submain- 
tenance  rations  being  consumed.  Accordingly,  the  total  ration 
contained  in  every  instance  a  considerable  excess  of  bases. 
Under  those  conditions,  not  only  the  feces  but  likewise  the 
urine  showed  an  excess  of  bases  over  acids,  i.e.,  the  animal 
was  engaged  in  getting  rid  of  excess  bases.  The  net  residue 
which  was  retained  in  the  body  consisted  of  basic  material  of 
rather  constant  composition  even  in  the  case  of  Diakow's  nearly 
mature  animal. 

So  far  as  they  go,  then,  these  experiments  confirm  the  con- 
clusion that  with  rations  containing  a  large  proportion  of 
roughage,  there  is  no  reason  to  fear  losses  either  specifically  of 
fixed  bases  or  in  general  of  total  ash.  Such  would  almost  always 
be  the  case  with  the  ordinary  maintenance  rations  of  cattle, 
sheep  and  horses.  Swine,  on  the  other  hand,  if  maintained 
entirely  on  grain,  might  very  well  receive  rations  not  well 
balanced  as  regards  ash,  and  experiments  and  observations 
which  are  discussed  in  Chapter  XI  (492-496)  seem  to  indicate 
that  even  for  maintenance  the  ordinary  grain  ration,  especially 
if  it  consists  largely  of  maize,  should  have  its  ash  composition 
corrected.  The  effect  of  an  acid  ash  in  the  mixed  rations  of 
herbivora,  and  the  extent  to  which  such  acidity  can  be  taken 
care  of  in  the  body  without  drawing  on  its  reserves  of  ash,  has 
still  to  be  investigated.  In  view  of  the  large  amounts  of  surplus 
bases  excreted  under  the  conditions  of  Diakow's  and  Cochrane's 
experiments,  it  would  seem  likely  that  even  a  considerable 
excess  of  acid  elements  might  be  neutralized  without  drawing 
on  the  stock  of  fixed  bases  in  the  body. 

In  Diakow's  experiments,  the  minimum  quantities  of  0.115 
Ib.  calcium  and  0.045  lb.  phosphorus  in  the  feed  per  1000  pounds 
live  weight  sufficed  to  support  not  inconsiderable  gains  by  the 
body.  In  Cochrane's  experiments,  a  minimum  of  0.147  Ib.  cal- 
cium per  1000  pounds  also  resulted  in  a  gain,  while  0.039  Ib. 
phosphorus  was  just  sufficient  for  maintenance.  In  Henneberg's 
investigations  3  upon  the  maintenance  of  cattle,  however,  dis- 

1  Landw.  Jahrb.,  44  (1913),  833.       2  Penna.  Inst.  of  An.  Nutr.,  unpublished  results. 
1  Beitrage,  etc.,  Heft,  1  (1860),  p.  113. 


346  NUTRITION  OF  FARM  ANIMALS 

tinctly  smaller  amounts,  viz.,  0.090  Ib.  of  calcium  and  0.021  Ib. 
of  phosphorus  proved  adequate  for  maintenance.  Weiske  l  found 
that  a  mature  sheep  gained  small  amounts  of  ash  ingredients 
on  a  ration  of  meadow  hay  containing,  per  1600  pounds  live 
weight,  0.179  Ib.  calcium  and  0.045  Ib.  phosphorus. 

436.  Correction  of  ash  deficiencies.  —  As  regards  main- 
tenance, it  seems  clear  that  the  ash  requirement  is  a  qualitative 
rather  than  a  quantitative  one;  i.e.,  that  it  is  the  proportions 
far  more  than  the  total  amounts  of  ash  ingredients  that  are 
important.  If,  then,  there  is  reason  to  fear  that  the  ash  supply 
in  the  ration  is  inadequate  for  maintenance,  any  measures 
taken  to  remedy  this  must  be  directed  chiefly  toward  the  cor- 
rection of  the  misproportion  between  different  ingredients  and 
only  secondarily  to  an  increase  of  their  total  quantity. 

One  method  of  effecting  such  a  correction  is  by  the  direct 
addition  of  mineral  matter.  In  attempting  to  correct  de- 
ficiencies in  this  way,  however,  the  simple  addition  of  more  ash 
material  to  the  ration  may  not  be  effective.  It  is  necessary 
also  to  take  into  account  the  nature  of  the  defects  to  be  made 
good.  Maize,  for  example,  has  already  been  instanced  (430) 
as  a  feeding  stuff  peculiarly  low  in  ash,  the  exclusive  use  of 
which,  even  for  maintenance,  might  readily  lead  to  a  loss  of 
ash  from  the  body.  Maize  is  especially  deficient  in  calcium  and 
its  exclusive  use  would  be  liable  to  cause  a  loss  of  this  element. 
The  attempt  to  supply  additional  calcium,  however,  by  the 
addition  of  such  materials  as  calcium  phosphate  or  sulphate 
would  not  help  the  situation  materially  because  the  ash  would 
still  remain  acid  and  thus  capable  of  causing  a  loss  of  fixed 
bases  irrespective  of  the  additional  amount  of  calcium  present. 
On  the  other  hand  the  addition  of  calcium  in  the  form  of  car- 
bonate, by  the  use  of  precipitated  chalk  or  wood  ashes,  not 
only  supplies  additional  calcium  but  remedies  the  acid  con- 
dition which  leads  to  a  loss  of  that  element,  as  has  been  well 
demonstrated  in  the  numerous  experiments  on  growing  swine 
referred  to  in  Chapter  XI  (496).  The  correction  of  the  ash 
composition  of  hays  causing  malnutrition  of  the  bones,  like 
those  instanced  by  Zuntz  (433),  presents  quite  different  re- 
quirements. The  very  injurious  Brandenburg  hay,  e.g.,  con- 
tained the  following  percentages  of  ash  ingredients :  — 

1  Landw.  Jahrb.,  9  (1880),  290. 


MAINTENANCE  —  REQUIREMENTS   OF   MATTER      347 

TABLE  64.  —  ASH  OF  HAY  CAUSING  RICKETS 


PER  CENT 

GRAM  EQUIVALENTS 

Acid 

Base 

CaO                    

0.693 
0.308 
1.762 
0.082 
2.650 
0.380 
0.722 

0.0668 
0-0535 
0.2037 

0.2470 
0.1526 

0-3737 
0.0264 

MeO 

K2O 

Na20    

SOs  (Estimated  from  protein)  .     .     . 
P2O5              

Cl    

0.3240 

0.7997 

Such  a  hay  is  relatively  deficient  in  calcium  and  phosphorus 
and  would  presumably  be  improved  by  the  addition  of  calcium 
phosphate,  while  the  addition  of  calcium  carbonate  would 
probably  be  unnecessary,  since  the  hay  contains  an  excess  of 
basic  over  acid  ingredients.  In  addition,  however,  to  its  de- 
ficiency in  calcium  and  phosphorus,  it  shows  a  misproportion 
of  potassium  to  sodium,  which,  as  already  explained,  would 
tend  to  increase  the  excretion  of  calcium  phosphate  unless 
sodium  salts,  particularly  the  chlorid,  were  added. 

In  the  mixed  rations  of  herbivora,  however,  direct  addition 
of  mineral  matter  is  seldom  likely  to  be  necessary  unless  rough- 
age of  abnormal  quality  is  employed.  Usually  the  surplus  of 
bases  in  forage  crops  will  more  than  balance  the  surplus  of 
acid  elements  in  the  concentrates  used,  while  the  common  salt 
ordinarily  given  as  a  condiment  will  more  than  balance  any 
probable  excess  of  potassium  in  the  rations.  Unusual  rations, 
such  perhaps  as  very  heavy  grain  rations,  those  containing  an 
unusual  proportion  of  protein,  or  those  made  up  of  unusual 
feeds  may  form  an  exception  to  this  general  rule  and  require 
special  consideration.  In  the  case  of  swine,  such  a  balancing 
of  one  feeding  stuff  against  another  as  regards  ash  ingredients 
is  less  practicable,  and  the  securing  of  a  proper  balance  needs 
more  attention.  Until,  however,  more  determinations  of  the 
actual  ash  balance  of  different  species  on  different  classes  of 
rations  are  made  (435)  it  is  hardly  possible  to  state  with  any 


348  NUTRITION  OF  FARM  ANIMALS 

definiteness  what  proportions  of  the  different  ash  elements  are 
required  in  maintenance  rations  and  the  whole  subject  offers 
a  wide  field  for  investigation. 

§  3.  ACCESSORY  SUBSTANCES 

Leaving  out  of  account  the  fact  that  the  proteins  are  a  minor 
source  of  energy  and  considering  (3nly  the  requirements  for 
matter,  the  proteins  and  ash  elements  of  the  feed  are  required 
substantially  for  maintenance,  i.e.,  to  make  good  losses  of  the 
structural  elements  of  the  body,  especially  if  the  ash  content 
of  the  body  fluids  be  included  under  this  designation.  Recent 
investigations,  however,  have  revealed  the  presence  in  the  feed 
of  minute  amounts  of  substances  which  appear  to  bear  quite 
a  different  relation  to  nutrition  and  which  may  be  called  for 
convenience,  accessory  substances. 

437.  Vitamins.  —  Attention  was  first  called  to  these  acces- 
sory substances  through  investigations  into  the  cause  of  the 
tropical  disease  known  as  beri  beri.  It  has  been  shown  that 
this  is  a  nutritional  disease,  resulting  from  a  preponderance  in 
the  diet  of  so-called  "  polished  "  rice,  i.e.,  rice  from  which  the 
seed  coats  have  been  removed.  It  is  a  tropical  disease  only  in 
the  sense  that  many  inhabitants  of  the  tropics  subsist  largely 
on  rice.  It  has  been  shown  that  it  can  be  produced  in  Europe 
by  the  excessive  use  of  this  grain. 

Substantially  the  same  disease  (polyneuritis)  may  be  induced 
in  animals,  especially  in  fowls,  by  an  exclusive  diet  of  polished 
rice  and  it  is  to  experiments  on  these  animals  that  most  of  our 
imperfect  knowledge  of  the  subject  is  due. 

It  has  been  shown  that  in  man  beri  beri  may  be  prevented 
by  the  use  of  a  rational  dietary,  and  especially  by  the  substitu- 
tion of  rough  rice  or  of  other  grains  for  polished  rice.  Experi- 
ments On  animals  have  shown  that  a  subject  fed  on  polished 
rice  until  nearly  at  the  point  of  death  may  be  restored  to  normal 
condition  in  a  short  time  by  the  administration  of  small  amounts 
of  an  aqueous  extract  of  rice  bran,  the  improvement  being  so 
rapid  as  to  appear  almost  miraculous.  The  generally  accepted 
explanation  is  that  the  bran  contains  a  small  amount  of  a  water- 
soluble  substance  or  substances  necessary  for  the  normal  func- 
tioning of  the  body,  the  lack  of  which  in  polished  rice  gives 


MAINTENANCE  —  REQUIREMENTS  OF  MATTER      349 

rise  to  the  disease.  Aqueous  extracts  of  other  substances, 
notably  yeast,  are  capable  of  producing  the  same  curative  effects. 
The  substances  themselves  have  not  yet  been  isolated  but 
Funk,1  who  has  been  prominent  in  this  line  of  investigation, 
has  given  them  the  general  name  of  vitamins.  It  is  thought 
that  other  nutritional  diseases,  such  as  scurvy  and  pellagra, 
as  well  as  the  cotton-seed  poisoning  of  swine,  are  likewise  due 
to  the  use  of  diets  deficient  in  these  vitamins. 

438.  Growth  substances.  —  Very  interesting  facts  of  a  some- 
what similar  character  have  been  observed  regarding  growth, 
notably  by  Hart  and  McCollum,  and  by  Osborne  and  Mendel.  It 
seems  to  have  been  demonstrated  that  there  are  associated  with 
certain  fats,  such  as  butter  fat,  the  fat  of  egg  yolks,  cod  liver 
oil,  etc.,  substances  whose  absence  from  a  ration  otherwise 
adequate  renders  it  incapable  of  permanently  supporting 
growth.  That  this  substance  (or  substances)  differs  from  the 
vitamins  of  Funk  seems  apparent  from  the  fact  that  normal 
maintenance  may  apparently  be  secured  on  rations  from  which 
it  is  absent. 

The  very  interesting  results  obtained  by  Hart,  McCollum, 
Steenbock  and  Humphrey 2  with  cows  fed  rations  properly 
balanced  according  to  the  ordinary  criteria  but  made  up  from 
the  products  of  single  plants  (wheat,  oats,  maize)  suggest  that 
substances  similar  to  the  vitamins  or  the  growth  substances 
may  play  an  important  part  in  the  nutrition  of  farm  animals. 
These  rations  when  continued  for  two  or  three  years  mani- 
fested specific  differences  in  nutritive  effect  as  regards  growth 
and  reproduction,  although  all  of  them  seemed  to  be  fairly  ade- 
quate for  the  maintenance  of  live  weight. 

Most  investigations  upon  these  accessory  substances,  however, 
have  been  directed  to  their  relation  to  growth  and  further 
discussion  of  their  functions  in  nutrition  may  therefore  be 
deferred  until  that  subject  is  considered. 

1  Ergeb.  Physiol.,  13  (1913),  125. 

2  Wis.  Expt.  Sta.,  Research  Bui.,  No.  17  (1911). 


CHAPTER  X 
THE   FATTENING    OF   MATURE    ANIMALS 

439.  Disposal  of  surplus  feed.  —  When  an  animal  consumes 
feed  in  excess  of  that  required  simply  for  maintenance,  a  pro- 
duction of  some  sort  results.     The  surplus  feed  may  be  trans- 
formed into  material  products  as  flesh,  fat,  milk,  etc.,  which 
are  stored  up  in  the  body  or  secreted,  or  it  may  be  katabolized 
and  its  energy  expended  in  the  performance  of  work. 

One  of  the  simplest  and  most  familiar  examples  of  such  pro- 
duction is  afforded  by  the  fattening  of  mature  animals.  Such 
fattening,  it  is  true,  is  not  of  great  economic  importance,  since 
the  larger  share  of  the  world's  meat  supply  is  derived  from 
animals  which  have  not  yet  reached  full  maturity.  Fattening, 
however,  as  well  as  growth,  forms  an  essential  part  of  the  pro- 
duction of  at  least  the  better  grades  of  meat,  and  while  it  is 
practiced  largely  on  immature  animals  its  feed  requirements 
can  be  studied  to  better  advantage  in  the  mature  animal.  The 
purpose  of  the  present  Chapter  is  to  consider  the  general  nature 
of  the  fattening  process  and  the  demands  which  it  makes  upon 
the  feed  supply,  leaving  its  economic  aspects  for  discussion  in 
connection  with  meat  production. 

440.  Fattening   requirements.  —  Just   as   the   quantities   of 
matter  and  energy  required  for  maintenance  depend,  in  the 
first  instance,  upon  the  amounts  lost  from  the  body  during 
fasting,  so  the  quantities  which  must  be  supplied  in  excess  of 
maintenance   to   support   the   fattening   process   will   depend 
primarily  on  the  amount  and  composition  of  the  gain  made. 
The  obvious  first  step  in  considering  the  feed  requirements  of 
the  fattening  animal,  therefore,  is  a  study  of  the  composition  of 
the  increase. 

§  i.  COMPOSITION  OF  THE  INCREASE  IN  FATTENING 

441.  Increase    chiefly    fat.  —  The    discussions    in    previous 
chapters  have  rendered  it  evident  that  the  chief  function  of 

350 


THE  FATTENING  OF  MATURE  ANIMALS  351 

the  fat  contained  in  the  animal  body  is  that  of  a  reserve  of 
energy  for  the  vital  activities,  which  may  be  drawn  upon  when 
the  feed  supply  is  insufficient  and  replaced  when  feed  is  abun- 
dant, while  the  protein  of  the  mature  animal  is  subject  to  much 
smaller  fluctuations.  It  would  be  expected,  therefore,  that  the 
gain  made  by  a  mature  animal  on  a  liberal  ration  would  consist 
largely  of  fat.  That  such  is  indeed  the  case  has  been  shown 
in  two  ways,  viz.,  by  means  of  comparative  analyses  of  the  car- 
casses of  lean  and  fattened  animals,  i.e.,  comparative  slaughter 
tests  (284),  and  by  means  of  balance  experiments  (285)  from 
which  the  composition  of  the  organic  matter  gained  may  be 
computed. 

442.  Comparative  slaughter  tests.  —  The  classic  example  of 
this  method  is  Lawes  and  Gilbert's  well-known  investigation  l 
into  the  composition  of  animals  slaughtered  for  human  food, 
the  results  of  which  are  recorded  in  Chapter  II  (97). 

The  two  pigs  analyzed  were  from  the  same  litter,  and  were  believed 
to  be  very  closely  comparable  at  the  beginning,  so  that  it  was  possible 
to  compute  directly  the  composition  of  the  increase  during  fattening. 
The  other  animals  analyzed  were  not  regarded  as  comparable.  In 
order  to  estimate  the  composition  of  the  increase  in  cattle  and  sheep, 
Lawes  and  Gilbert  compute  the  weights  of  protein,  fat,  ash  and  total 
dry  matter  contained  in  the  bodies  of  a  large  number  of  animals 
before  and  after  fattening,  using  in  the  former  case  the  analytical 
results  obtained  on  the  half-fat  ox  and  the  store  sheep  and  in  the 
latter  those  on  the  fat  ox  and  fat  sheep.  The  differences,  of  course, 
show  the  gain  of  each  ingredient.  In  the  case  of  sheep  and  swine, 
they  utilize  the  results  of  their  own  fattening  experiments.  In  the 
case  of  cattle,  the  computations  are  based  upon  the  results  of  experi- 
ments by  others.  The  oxen  whose  composition  was  compared  were 
mature  animals.  The  sheep,  on  the  other  hand,  were  yearlings. 
Neither  the  age  nor  the  weight  of  the  pigs  is  stated,  but  their  pig 
feeding  experiments  in  general  were  made  with  animals  ranging  from 
somewhat  over  100  Ib.  to  160  Ib.  in  weight.  The  results  as  to  this 
species,  therefore,  presumably  relate  to  only  partially  mature  animals. 

In  1876-1877,  Henneberg,  Kern  and  Wattenberg 2  investigated 
the  composition  of  the  increase  in  weight  of  mature  sheep  in 
fattening.  Their  analyses  were  of  the  carcasses  only  but  the 

1  Phil.  Trans.,  II,  1859,  p.  493.  2  Jour.  Landw.,  26  (1878),  545. 


352 


NUTRITION  OF   FARM   ANIMALS 


weights  of  the  offal  parts  were  recorded,  so  that  it  is  possible 
to  compute  approximately  the  weight  of  the  fat-free  body, 
exclusive  of  the  contents  of  the  digestive  tract  and  of  the  wool. 
Similar  comparisons  based  on  75  and  82  day  fattening  periods 
with  swine  were  reported  by  Soxhlet l  in  1881  and  the  results 
of  short  fattening  experiments  (16  to  37  days)  on  geese  by  B. 
Schulze  2  in  1882  and  by  Chaniewski3  in  1884,  the  primary 
object  of  each  case  being  a  study  of  the  sources  of  animal  fat. 
Friske4  in  1909  and  Pfeiffer  and  Friske5  in  1911,  in  a  study  of  the 
gain  of  protein  by  mature  animals  during  a  fattening  period  of 
about  100  days,  likewise  reported  a  number  of  partial  analyses 
of  mature  sheep  similar  to  those  made  by  Henneberg,  Kern 
and  Wattenberg. 


TABLE  65.  —  COMPOSITION  OF  INCREASE  IN  LIVE  WEIGHT  IN  FATTENING 


AVERAGE 
AGE  OF 
ANIMAL 

COMPOSITION  OF  INCREASE 

ENERGY 
CONTENT 

OF 

INCREASE, 
CALORIES 
PER  LB. 

Water 

% 

Ash 

% 

Protein 

% 

Fat 

% 

Cattle 

Lawes  and  Gilbert      .     . 

4  years 

24.64 

1.47 

7.69 

66.2O 

3051 

Sheep 

Lawes  and  Gilbert      .     . 

TT                  "U                         T7"                                 J 

ij  years 

20.13 

2-34 

7-13 

70.40 

3218 

Henneberg,     Kern     and 

Wattenberg     .     .     . 

Fat 

2T  years 

25.80 

6.64 

67.  =56 

3083 

Very  fat     

2\  years 

20.30 

W.  Wif. 

5-23 

w  /    0 

74-47 

v5wuo 

3344 

Last  stage  of  fattening 

2  f  years 

6-45 

1.68 

91.87 

4002 

Friske 

4.  vears 

12  O3 

1^.07 

72.QO 

2r  -?i 

Pfeiffer  and  Friske      .     . 

*T    J  ^t*fi  ° 

3^  years 

x  *  '^O 

64.33 

*  O  "w  / 

7.11 

/     «v 

28.56 

ooo 
1415 

Swine 

Lawes  and  Gilbert  (Aver- 

,                          , 

age)  

— 

22.OO 

O.o6 

6.44 

71-50 

3247 

Soxhlet  —  Swine  No.  2   . 

i6|  mos. 

58.96 

3-17 

13.42 

24-45 

1401 

Swine  No.  3    . 

16^  mos. 

35-99 

3-62 

6.80 

53.59 

2485 

Geese 

Schulze     

9  mos. 

37.06 

1.  21 

3-34 

58.39 

2602 

Chaniewski   

— 

24.15 

i-37 

3.02 

61.46 

2726 

1  Centbl.  Agr.  Chem.,  10  (i$8i),  674.  3  Ztschr.  Biol.,  20  (1884),  179. 

2  Landw.  Jahrb.,  11  (1882),  57.  4  Landw.  Vers.  Stat.,  71  (1009),  441. 

6  Ibid.,  74  (1911),  409. 


THE  FATTENING  OF  MATURE  ANIMALS 


353 


The  results  of  these  comparative  slaughter  tests,  so  far  as 
they  relate  to  the  composition  of  the  increase,  are  summarized 
in  Table  65,  which  includes  also  the  computed  energy  content 
of  the  increase. 

443.  Respiration  experiments.  —  Respiration  experiments  on 
mature  animals  have  fully  confirmed  the  results  of  slaughter 
tests  as  regards  the  proportion  of  protein  to  fat  in  the  increase, 
as  appears  from  the  summary  of  Table  66. 

By  far  the  most  extensive  respiration  experiments  are  those  made 
at  the  Moeckern  Experiment  Station  1  by  G.  Kiihn  and  by  Kellner 
on  mature  fattening  cattle.  Of  the  60  reported  experiments  in 
which  there  was  a  gain  of  both  protein  and  fat,  only  3  show  less 
than  70  per  cent  of  fat  in  the  total  organic  matter  gained  and  only 
3,  a  percentage  above  95.  Rejecting  these  6  and  grouping  the  re- 
mainder according  to  the  percentage  of  fat  gives  the  results  shown 
in  the  first  five  lines  of  the  table.  To  these  are  added  the  results  of 
earlier  experiments  by  Henneberg,  Fleischer  and  Miiller  2  on  sheep 
and  by  Meissl 3  on  swine.  The  gains  of  ash  and  of  water  were  not 
determined  in  these  experiments. 

TABLE  66.  —  PROPORTIONS  OF  PROTEIN  AND  FAT  IN  FATTENING  INCREASE 


RANGE  OF 
PERCENTAGE 
or  FAT  IN 
ORGANIC 
MATTER 
GAINED 

AVERAGE  COMPOSITION 
or  ORGANIC  MATTER 
OF  GAIN 

Total 
Protein 

Fat 

Kellner  —  Experiments  on  cattle 
Group  I      
Group  II     

% 
70-74.99 
75-79.99 
80-84.99 
85-89.99 
90-94.99 

% 
26.25 
23.30 
17.17 

12-55 
8.06 

4.26 

9-75 
10.67 
16.39 
15.16 

% 

73-75 
76.70 
82.83 

87.45 
91.94 

95-74 

90.25 
89.33 
83-61 
84.84 

Group  III 

Group  IV    
Group  V     

Henneberg,  Fleischer  and  Miiller  —  Ex- 
periments on  sheep   
Meissl,  Strohmer  and  Lorenz  —  Experi- 
ments on  swine 
Animal  No.  i       
Animal  No   2 

Animal  No.  3       
Animal  No.  4       

1  Landw.  Vers.  Stat.,  44  (1894),  370;   53  (1900),  i. 

2  Jahresber,  Agr.  Chem.,  lfr-17  (1876),  II,  145.          8  Ztschr.  Biol.,  22  (1886),  63. 

2  A 


354 


NUTRITION  OF  FARM  ANIMALS 


Both  the  respiration  experiments  and  the  comparative 
slaughter  tests  demonstrate  that  the  fattening  of  a  mature 
animal  is,  as  its  name  implies,  largely  a  production  of  fat, 
which  is  deposited  chiefly  in  the  sub-cutaneous  and  internal 
adipose  tissue  and  to  a  limited  extent  also  in  the  muscles.  A 
few  of  the  comparative  slaughter  tests  show  a  large  storage  of 
water  but  the  organic  matter  gained  in  every  case  was  chiefly 
fat.  On  the  average  of  all  the  foregoing  experiments  by  both 
methods,  the  composition  of  the  organic  matter  stored  up  in  the 
body  of  the  fattening  animal  was  as  follows :  - 

TABLE  67.  —  AVERAGE  COMPOSITION  or  ORGANIC  MATTER  GAINED  IN 

FATTENING 


MEAN 

MAXIMUM 

MINIMUM 

Fat      

87.16% 

QCT  74% 

64.  17% 

Protein                   . 

12  SA% 

?r  42% 

A  26% 

100.00% 

— 



444.  The  gain  of  protein.  —  The  foregoing  data  also  show, 
however,  that  while  the  gain  of  dry  matter  in  fattening  consists 
chiefly  of  fat  there  is  also  a  gain  of  more  or  less  protein  and  of 
small  amounts  of  mineral  matter. 

The  actual  gain  of  protein  in  some  cases  was  not  inconsiderable. 
This  appears  from  Table  68,  which  includes  both  slaughter  tests  and 
metabolism  experiments,  most  of  which  are  identical  with  those  from 
which  the  composition  of  the  increase  has  been  calculated. 

It  is  probably  safe  to  assume  that  in  most  of  these  experi- 
ments the  feed  contained  a  considerable  surplus  of  protein 
over  that  necessary  for  maintenance.  Such  a  surplus  of  pro- 
tein, as  was  shown  in  Chapter  IX  (406),  has  a  tendency  to  pro- 
duce a  somewhat  limited  storage  of  protein,  which  probably  con- 
sists in  an  increase  of  the  contents  of  the  cells  or  of  the  protein 
held  in  solution  in  the  body  fluids  rather  than  in  an  increase  of  the 
structural  elements  of  the  body.  The  observed  gain,  therefore, 
may  represent  in  part  an  actual  increase  in  the  cell  protoplasm 
or  in  the  soluble  protein  of  the  body,  while  in  addition,  a  rela- 
tively small  amount  is  accounted  for  by  the  growth  of  hoof, 
horn,  epidermis,  etc.,  of  the  cattle  and  swine.  Moreover, 


THE   FATTENING  OF  MATURE  ANIMALS 


355 


while  the  laying  on  of  fat  is  accomplished  largely  by  an  increase 
in  the  fat-content  of  existing  cells  there  appears  to  be  also  an 
increase  in  the  number  of  cells  in  the  adipose  tissue,  and  the 
latter  process  may  be  assumed  to  require  a  supply  of  protein. 
The  protein  contained  in  one  pound  of  subcutaneous  adipose 
tissue  of  average  composition  would  be  equivalent  to  the 
storage  of  about  0.045  MJ>.  °f  protein.  Obviously,  however,  the 
growth  of  epidermal  and  adipose  tissue  can  but  partially  ac- 
count for  the  observed  gain  of  protein  in  many  of  these  instances 
and  apparently  a  distinct  increase  of  the  nitrogenous  tissue  in 
fattening  must  be  admitted,  averaging,  in  these  experiments, 
about  0.2  pound  per  day  and  1000  pounds  live  weight  or  about 
5.5  per  cent  of  the  total  increase  in  live  weight. 

TABLE  68.  —  GAIN  OF  PROTEIN  BY  MATURE  ANIMALS 


CHARACTER  OF 
EXPERIMENT 

AVER- 
AGE 
LIVE 
WEIGHT 

DAILY  GAIN  OF 
PROTEIN 

Per 
Head 

Per  1000 
Live  Wt 

Cattle 
Kiihn  and  Kellner  
Sheep  1 
Henneberg,  Fleischer    and  Miil- 
ler 

Metabolism 

Metabolism 
Metabolism 

Slaughter 
Metabolism 
Metabolism 
|  Metabolism  * 
[  Slaughter 
J  Metabolism 
[  Slaughter 

Slaughter 
Metabolism 

Slaughter 

Kgs. 
667 

34-2 
54-8 

48.3 
43-5 
38.5 
35-2 
35-2 
36.7 
30.7 

"7-5 
70.0 
104.0 
125.0 
140.0 

3-9 

Grams 
82.0 

8.50 
9.24 

4-05 
10.36 

6-55 
21.49 
8.42 

7.67 
4-55 

51.96 
46.92 
43-32 
32.76 
36-48 

36.45 

0.123 

0.248 
0.169 

0.084 
0.238 
0.170 
0.611 
0.239 
0.209 
0.124 

0.442 
0.670 
0.416 
0.262 
0.261  . 

9-346 

Weiske       .... 

Henneberg,    Kern   and   Watten- 
berff  . 

Henneberg  and  Pfeiffer    . 
Pfeiffer  and  Kalb    
Friske    

Pfeiffer  and  Friske  

Swine 
Soxhlet       

Meissl  

Geese 
Schulze      

1  The  nitrogen  of  the  wool  is  not  included  in  the  gain. 

2  The  same  animals  were  used  also  in  the  slaughter  tests. 


356  NUTRITION  OF  FARM  ANIMALS 

445.  Influence  of  fattening  on  the  composition  of  the  lean 
meat.  —  While  fattening  consists  largely  in  an  increase  of  adi- 
pose tissue  in  the  ordinary  sense,  it  has  an  important  effect 
both  upon  the  composition  of  lean  meat  in  the  commercial 
sense  and  upon  that  of  the  muscle  tissue  proper  (fat-free 
lean  meat). 

Percentage  0}  fat.  —  What  is  commonly  spoken  of  as  lean 
meat  is  by  no  means  free  from  fat,  since  the  term  includes  not 
only  muscular  fibers  themselves  with  the  relatively  little  fat 


FIG.  37.  —  The  marbling  of  meat.     Porterhouse  steak  from  a  prime  steer. 
(Illinois  Experiment  Station.) 

which  they  contain,  but  the  masses  of  connective  tissue  of  all 
degrees  of  magnitude  found  between  the  muscle  bundles  and 
between  the  separate  muscles  (86).  Fattening,  especially  in- 
tensive fattening,  may  cause  a  marked  increase  in  the  storage 
of  intramuscular  fat  in  the  lean  meat,  as  is  evident  to  the  eye 
in  the  so-called  "  marbling." 

Such  analyses  of  lean  meat  as  are  recorded  confirm  the  evi- 
dence of  the  eye  in  this  respect.  A  summary  of  the  results  on 
this  point  has  been  given  by  the  writer  1  elsewhere.  The  fol- 
lowing example  taken  from  that  publication  may  serve  to 
illustrate  the  point  in  question. 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  108  (1908),  p.  33. 


THE  FATTENING  OF  MATURE  ANIMALS  357 

TABLE  69.  —  FAT  IN  FRESH  LEAN  MEAT  —  LEYDER  AND  PYRO 


LEAN  Cow 

% 

FAT  Ox 

•    % 

VERY  FAT 
Cow 

% 

Neck  

1.3 

I.O 

2.8 

Leg                         

O.Q 

4  ° 

1  8 

Flank       

0.8 

42 

8.8 

Tenderloin                  .                   . 

2  6 

8  o 

I  2  O 

Similarly,  Braman  l  found  the  following  percentages  of  fat 
in  lean  meat  from  a  medium  fat  (common)  and  a  well-fattened 
(prime)  steer. 

TABLE  70.  —  FAT  IN  FRESH  LEAN  MEAT  —  BRAMAN 


COMMON 

STEER 

PRIME 

STEER 

Porterhouse 

6  72 

1  2  71 

Round 

?     '7A 

6  66 

A  practical  difficulty  in  making  such  comparisons  arises  in  the 
preparation  of  the  sample.  Obviously,  the  subcutaneous  fat  sur- 
rounding the  meat  should  be  discarded  and  the  same  is  true  of  the 
large  masses  of  fat  found  between  the  muscles,  but  just  what  part  of 
the  adipose  tissue  scattered  through  the  meat  of  a  fat  animal  should 
be  regarded  as  mechanically  separable  and  what  part  should  be  re- 
garded as  belonging  to  the  meat  proper  is  difficult  to  decide.  Dif- 
ferences in  the  trimming  of  the  pieces  may  account  for  some  of  the 
irregular  results  found  by  recent  experimenters. 

Extractives.  —  It  appears  to  be  established  that  fattening 
increases  the  nitrogenous  extractives  of  the  muscles  as  well  as 
causes  a  deposition  of  fat  in  and  about  them.  For  example, 
in  Henneberg,  Kern  and  Wattenberg's  experiments  on  sheep, 
included  in  Table  65,  the  composition  of  the  meat  from  the  lean 
and  from  the  very  fat  animal  (partially  freed  from  connective 
tissue)  computed  to  the  fat-free  state,  was :  — 

llbid.,  Bui.  128  (1908),  p.  86. 


358  NUTRITION  OF   FARM  ANIMALS 

TABLE  71.  —  COMPOSITION  OF  FAT-FREE  MEAT  OF  SHEEP 


THIN  SHEEP 

% 

VERY  FAT  SHEEP 

C7 
70 

Water                                              .     .     . 

70  4-1 

7Q  O2 

Insoluble  protein 

IS  8^ 

T  c  72 

Extractives 
Soluble  protein   
Non-protein 

I.2Q 
2  l8 

1-93 

2  17 

Ash  

I  27 

I  1^ 

Total  extractives          

A  74. 

ET    2C 

IOO.OO 

IOO.OO 

It  is  computed  that  the  actual  gains  during  the  fattening  of 
the  fat  animal  were  as  follows :  — 

Insoluble  protein 38.7  Grms. 

Extractives : 

Protein 82.0  Grms. 

Non-protein 4.2  Grms. 

Ash —9.2  Grms. 

77.0  Grms. 


Total        115.7  Grms. 

Somewhat  similar  results  were  obtained  later  by  the  same 
authors  in  experiments  on  fattening  lambs.  Evidently  this 
increase  in  the  soluble  nitrogenous  compounds  of  the  muscles 
is  one  of  the  factors  going  to  make  up  the  observed  gain  of 
protein  by  fattening  animals. 

446.  Object  of  fattening.  —  The  fattening  of  animals  as  a 
commercial  process  is  a  practice  based  on  experience,  which 
has  shown  that  the  tenderness  and  palatability  of  the  meat  are 
materially  increased  thereby,  so  that  the  consumer  is  willing  to 
pay  a  higher  price  for  it.  It  is  to  this  improvement  in  quality 
in  the  first  instance,  and  only  secondarily  to  the  gain  in  weight, 
that  the  feeder  looks  for  his  profit. 

The  facts  as  to  the  composition  of  the  increase  in  fattening 
recorded  in  the  foregoing  paragraphs  serve  to  show  what  are 
the  principal  factors  in  this  improvement  in  the  quality  of  the 
meat.  They  are,  first,  the  deposition  of  the  intermuscular 


THE  FATTENING  OF  MATURE  ANIMALS  359 

and  intramuscular  fat,  and,  second,  an  increase  in  the  muscular 
tissues  themselves,  due  in  part  at  least  to  an  increase  in  the 
soluble  protein  and  in  the  nitrogenous  extractives.  The  dep- 
osition of  fat  adds  directly  to  the  nutritive  value  of  the  meat, 
materially  increasing  its  fuel  value.  Moreover,  its  mechanical 
effect  in  separating  the  fibers  may  be  presumed  to  render  the 
meat  more  tender,  while  the  products  of  its  decomposition  in 
some  forms  of  cooking  (roasting  and  broiling)  probably  add  to 
the  flavor  of  the  meat.  The  increase  of  the  soluble  protein  is 
also  doubtless  one  cause  of  the  tenderness  of  the  meat  of  fat- 
tened animals,  while  the  other  nitrogenous  matters,  though 
of  little  or  no  direct  nutritive  value,  are  an  improvement  through 
the  added  flavor  and  palatability  which  they  bring  about. 

§  2.    FEED  REQUIREMENTS  FOR  FATTENING 

447.  Comparison  with  maintenance.  —  In  the  two  preceding 
chapters  it  appeared  that  the  maintenance  requirements  are 
determined  substantially  by  the  amounts  of  protein  and  of 
energy  which  are  katabolized  in  fasting  and  which,  therefore, 
must  be  made  good  from  the  feed  in  order  to  maintain  the  body. 
By  analogy,  the  amounts  of  protein  and  energy  stored  up  in  the 
process  of  fattening  may  be  taken  as  the  measure  of  the  require- 
ments for  fattening  —  i.e.,  of  the  amounts  which  the  feed  must 
be  capable  of  supplying  in  an  available  form.  In  other  words, 
the  requirements  for  fattening  are  equivalent  to  the  tissue 
produced  just  as  the  requirements  for  maintenance  are  equiva- 
lent to  the  tissue  whose  loss  is  to  be  prevented.  The 
total  feed  requirement  of  a  fattening  animal,  then,  is  to  be 
regarded  as  made  up  of  the  maintenance  requirement  plus  the 
fattening  requirement. 

In  one  important  respect,  however,  the  fattening  require- 
ment differs  from  the  maintenance  requirement.  The  latter, 
while  not  invariable,  is  still  more  or  less  constant  for  the  same 
animal.  In  fattening,  on  the  other  hand,  there  may  be  a 
varying  rate  of  production  up  to  the  limit  set  by  the  in- 
dividuality of  the  animal  and  its  capacity  to  eat  and  digest 
food.  Accordingly,  as  slow  or  rapid  fattening  is  anticipated 
or  desired,  the  daily  requirement  of  the  animal  may  be  higher 
or  lower. 


NUTRITION  OF  FARM  ANIMALS 


Net  energy  values  for  fattening 

448.  General  conception.  —  Physiologically,  the  process  of 
fattening  may  be  regarded  as  a  storing  up  by  the  animal,  against 
a  possible  future  scarcity,  of  feed  energy  supplied  in  excess  of 
its  immediate  needs. 

This  storage  of  .energy  is  not  accomplished  without  some  loss. 
As  in  maintenance  feeding,  so  in  fattening,  a  considerable 
portion  of  the  feed  energy  escapes  utilization  for  one  reason  or 
another.  The  conception  of  the  net  energy  value  as  express- 
ing that  part  of  the  feed  energy  which  remains  available  after 
these  various  losses  have  been  deducted,  has  been  considered 
in  Chapter  VIII.  The  same  conception  may  be  extended  to 
fattening  rations.  Just  as  the  net  energy  value  of  a  feed  for 
maintenance  is  measured  by  the  loss  of  body  energy  which  it 
prevents,  so  its  net  energy  value  for  fattening  is  measured  by 
the  storage  of  body  energy  brought  about. 

449.  Method  of  determination.  —  This  conception,  as  well 
as  the  method  of  determining  the  net  energy  value  for  fatten- 
ing, may  be  illustrated  by  the  following  respiration  experiment 
by  Kellner  upon  a  mature  ox,  in  which  meadow  hay  was  added 
to  a  mixed  basal  ration  already  sufficient  to  cause  some  gain. 
The  second  column  of  the  table  shows  the  metabolizable  energy 
of  the  two  rations,  the  third  column  the  computed  heat  pro- 
duction, and  the  fourth  the  energy  contained  in  the  observed 
gain  of  protein  and  fat. 

TABLE  72. —  DETERMINATION  OF  NET  ENERGY  VALUE  FOR  FATTENING 


HAY 
ADDED  TO 
BASAL 
RATION 

METABO- 
LIZABLE 
ENERGY  OF 
RATION 

COMPUTED 
HEAT 
PRO- 
DUCED 

ENERGY  OF 
FAT  AND 
PROTEIN 
GAINED  BY 
BODY 

Lb. 

Therms 

Therms 

Therms 

Basal  ration  +  hay     .... 

7-7 

23.14 

18.90 

4.24 

Basal  ration  

— 

17.64 

15.62 

2.  02 

Difference 

7  7 

5cjO 

^  28 

2   22 

Difference  per  Ib.  of  hay      .     . 

0.714 

0.426 

0.288 

Each  pound  of  hay  added  to  the  basal  ration  resulted  in  a 
gain  of  protein  and  fat  containing  0.288  Therm  of  energy. 


THE  FATTENING  OF  MATURE  ANIMALS1  361 

This  was  its  net  energy  value  for  fattening.  A  comparison 
with  Table  37  in  Chapter  VIII  (364),  showing  the  results  of  a 
determination  of  the  net  energy  value  for  maintenance,  renders 
evident  the  identity  of  the  method  employed  in  the  two  cases, 
the  only  difference  being  that  in  one  case  the  comparison  be- 
tween the  two  rations  is  made  below  the  point  of  maintenance 
and  in  the  other  case  above  it.  It  is  evident  that  in  fattening, 
as  in  maintenance  feeding,  there  is  a  considerable  expenditure 
of  energy  consequent  upon  the  consumption  of  feed,  so  that, 
only  part  of  the  metabolizable  energy  is  actually  stored  up  in 
the  gain  by  the  oody.  In  the  experiment  given  as  an  illus- 
tration, one  pound  of  the  hay  contained  0.714  Therm  of 
metabolizable  energy,  of  which  only  0.288  Therm  or  40.7  per 
cent  was  recovered  in  the  gain. 

450.  Relative  values  for  maintenance  and  for  fattening.  - 
The  same  causes  which  were  considered  in  Chapter  VIII  (367) 
are  of  course  operative  to  bring  about  the  increased  expendi- 
ture of  energy  on  the  heavier  rations  of  the  fattening  animal. 
In  addition,  it  would  appear  that  the  chemical  changes  in- 
volved in  the  formation  of  fat  from  proteins  and  carbohydrates 
would  result  in  more  or  less  evolution  of  heat.     Whatever 
expenditure  of  energy  may  be  thus  caused  is  additional  to  that 
caused  directly  by  feed  consumption  under  maintenance  con- 
ditions and  must  evidently  tend  to  reduce  the  net  energy  value 
of  the  feed  by  a  corresponding  amount ;  in  other  words,  the  net 
energy  values  of  feeding  stuffs  for  fattening  would  tend  to  be 
lower  than  those  for  maintenance.     Such  data  as  are  available, 
however,  do  not  appear  to  indicate  that  this  difference  is  a 
considerable  one  in  the  case  of  farm  animals,  and  it  would  appear 
that,  in  the  case  of  cattle  at  least  and  presumably  in  that  of  other 
species,  the  net  energy  values  of  feeding  stuffs  may  be  regarded 
as  being  substantially  the  same  for  fattening  as  for  maintenance.1 

Energy  requirements  for  fattening 

451.  Energy  content  of  gain.  —  Since  the  net  energy  value 
of  a  feeding  stuff  or  ration  for  fattening,  as  explained  in  the 
foregoing  paragraphs,  is  that  part  of  its  total  energy  which  can 
be  stored  up  by  the  animal  in  the  increase,  it  follows  that  the 

1  Compare  Armsby  and  Fries,  Jour.  Agri.  Research,  3  (1915).  435- 


362  NUTRITION  OF  FARM   ANIMALS 

ration  of  such  an  animal  must  supply  an  amount  of  net  energy 
equal  to  the  maintenance  requirement  plus  the  quantity  of 
energy  contained  in  the  gain  made.  The  latter  quantity,  how- 
ever, may  be  computed  approximately  from  the  data  given  in 
§  i  regarding  the  chemical  composition  of  the  increase  in  live 
weight  during  fattening.  Estimating  the  energy  content  of 
protein  at  2586  Cals.  per  pound  (5.7  Cals.  per  gram)  and  that 
of  fat  at  4309  Cals.  per  pound  (9.5  Cals.  per  gram),  the  energy 
content  of  one  pound  of  increase  was  as  shown  in  the  last  col- 
umn of  Table  65  (442). 

Excluding  two  apparently  questionable  results,1  the  range 
and  average  of  the  remainder  are  as  follows.  Although  some- 
what variable  they  indicate  that  on  the  average  of  an  entire 
fattening  period  a  pound  of  increase  in  live  weight  in  cattle, 
sheep  and  swine  is  equivalent  to  about  3.25  Therms. 

TABLE  73.  —  ENERGY  PER  POUND  INCREASE  IN  LIVE  WEIGHT 

Maximum 4.002  Therms 

Minimum 2.485  Therms 

Average 3-245  Therms 

452.  Influence  of  stage  of  fattening.  —  The  results  just  cited 
are  in  most  cases  those  of  an  entire  fattening  period.  There 
can  be  little  doubt,  however,  that  the  composition  of  the  in- 
crease and  its  energy  content  vary  materially  as  the  fattening 
advances. 

This  appears  clearly  from  Henneberg,  Kern  and  Wattenberg's  re- 
sults upon  sheep.  The  "fat"  animal  had  been  fed  for  10  weeks  and 
was  regarded  as  fat  according  to  local  standards.  The  "very  fat" 
animal  had  been  fed  for  29  weeks,  or  until  no  further  gain  in  live 
weight  occurred.  As  the  table  shows,  the  total  gain  by  the  "very 
fat"  animal  contained  materially  lower  percentages  of  water,  ash 
and  protein  and  a  higher  percentage  of  fat,  and  had  a  10  per  cent 
higher  energy  content  than  the  gain  by  the  "fat"  animal,  while  a  com- 
parison between  the  "fat"  and  the  "very  fat"  animals  shows  the 
gain  made  by  the  latter  during  the  last  19  weeks  of  fattening  to  have 

1  Pfeiffer  and  Friske's  results  appear  exceptional,  since  the  gain  apparently  con- 
sisted to  an  abnormally  large  extent  of  water,  while  the  authors  themselves  point  out 
that  the  gains  of  dry  matter  were  notably  less  than  should  have  been  produced  from 
the  feed  consumed.  It  would  seem,  therefore,  that  their  omission  is  justified.  Soxh- 
let's  result  upon  swine  No.  i  has  also  been  omitted  for  a  similar  reason. 


THE   FATTENING  OF  MATURE  ANIMALS  363 

contained  nearly  92  per  cent  of  fat  and  to  have  had  an  energy  content 
of  4002  Cals.  per  pound.  The  same  investigators  also  obtained  en- 
tirely similar  results  in  the  fattening  experiments  on  lambs  cited  in 
Chapter  XI  (458)  although  naturally  the  proportions  of  water  and 
protein  in  the  increase  were  greater  than  in  the  case  of  the  mature 
sheep. 

During  the  earlier  stages  of  fattening,  especially  with  thin 
animals,  the  storage  of  fat  is  accompanied  by  a  considerable 
gain  of  water  and  by  more  or  less  increase  in  body  protein.  As 
the  fattening  progresses,  however,  the  gain  comes  to  consist 
to  an  increasing  extent  of  fat  accompanied  by  very  little  protein 
and  a  relatively  small  percentage  of  water.  The  energy 
content  of  a  unit  of  gain  in  live  weight,  therefore,  in  the  later 
stages  of  fattening  is  materially  greater  than  in  the  earlier 
stages  of  the  process.  Evidently,  then,  more  net  energy  will 
be  required  in  a  fattening  ration  to  produce  a  pound  of  increase 
in  live  weight  toward  the  close  of  the  fattening  process  than  at 
its  beginning,  a  fact  which  is  entirely  in  harmony  with  the  ex- 
perience of  feeders  that  gains  become  increasingly  expensive  as 
the  animals  become  fatter. 

So  far  as  definite  conclusions  are  warranted  from  the  rather 
scanty  data  available,  it  would  seem  that  in  the  earlier  stages 
of  fattening  a  ration  supplying  (in  addition  to  maintenance) 
about  2.5  Therms  of  net  energy  would  be  sufficient  to  support 
a  gain  of  a  pound  of  live  weight,  while  in  the  later  stages  the 
requirement  may  rise  to  4.0  Therms  or  perhaps  even  more. 

Protein  requirements  for  fattening 

453.  Protein  unnecessary  for  fat  production.  —  It  was 
shown  in  Chapter  V  (247-249)  that  body  fat,  especially  in  the 
case  of  farm  animals,  is  derived  chiefly  from  the  non-nitrog- 
enous nutrients  of  the  feed,  protein  playing  but  a  subordinate 
role  in  its  production,  and  Kellner  has  shown  (769)  that  the 
proportion  of  the  energy  of  protein  which  can  be  stored  up  by 
mature  fattening  animals  is  distinctly  less  than  the  correspond- 
ing percentage  for  the  non-nitrogenous  nutrients.  So  far  as 
simple  fat  production  is  concerned,  therefore,  it  would  appear 
that  a  surplus  of  protein  over  that  required  for  maintenance 
would  be  unnecessary  and  possibly  disadvantageous  on  account 


364  NUTRITION  OF  FARM  ANIMALS 

of  its  tendency  to  stimulate  the  general  metabolism  of  the  body 
(365). 

454.  Protein  in  increase.  —  As  appeared  in  §  i  (444),  how- 
ever, the  actual  increase  in  mature  fattening  animals  has  been 
found  to  contain  a  relatively  small  and  rather  variable  propor- 
tion of  protein,  due  in  part  to  the  growth  of  epidermal  tissue, 
in  part  to  an  increase  in  the  number  of  fat  cells,  and  in  part 
to  an  actual  storage  of  protein  and   nitrogenous   extractives 
in  the  muscular  tissue  (and  in  the  internal  organs?).     It  is  to 
be  remarked,  however,  that  in  most  or  all  instances  the  rations 
consumed  contained  more  protein  than  was  necessary  for  main- 
tenance, with,  of  course,  an  abundant  supply  of  non-nitrog- 
enous material,  so  that  the  conditions  were  favorable  for  such 
a  storage  of  protein  as  that  just  mentioned.     So  far  as  the  writer 
is  aware,  it  has  not  yet  been  shown  that  the  mature  fattening 
animal  actually  requires  any  surplus  of  protein  over  the  amount 
necessary  for  maintenance,  although  it  can  apparently  utilize  an 
excess,  at  least  to  some  extent,  to  increase  the  stock  of  protein 
in  its  body. 

At  most,  the  requirement  of  the  fattening  animal  as  meas- 
ured by  the  observed  storage  of  protein  is  relatively  small,  one 
pound  of  increase  in  live  weight  containing  in  round  numbers 
from  0.02  Ib.  to  0.08  Ib.  of  protein. 

455.  Utilization  of  feed  protein.  —  Assuming  the  observed 
gain  of  protein  by  the  fattening  animal  to  represent  a  real  re- 
quirement, it  is  evident  that  a  sufficient  fattening  ration  must 
supply,  in  addition  to  the  protein  necessary  for  maintenance, 
an  additional  amount  sufficient,  after  undergoing  the  various 
processes  of  digestion  and  metabolism,  to  yield  the  amount  of 
body  protein  contained  in  the  increase  of  body  weight.     As 
will  appear  more  particularly  in  considering  the  subject  of 
growth  (470,  471),  little  is  known  regarding  the  amount  of  feed 
protein  required  to  yield  a  unit  of  body  protein.     Doubtless 
this  will  differ  as  between  different  individual  proteins,  depend- 
ing, for  one  thing,  upon  the  proportions  of  the  different  amino 
acids  which  they  contain,  but  adequate  quantitative  data  are 
as  yet  unavailable. 

456.  Protein  in  fattening  rations.  —  In  the  absence  of  definite 
knowledge  regarding  the  availability  of  the  protein  of  the  feed, 
the  question  of  the  amount  of  this  nutrient  which  should  be 


THE  FATTENING  OF  MATURE  ANIMALS  365 

supplied  to  fattening  animals  may  be  approached  much  as  was 
the  question  of-  the  amount  necessary  for  maintenance  in  Chap- 
ter IX,  i.e.,  by  inquiring  what  is  the  least  amount  of  digestible 
protein  which,  along  with  sufficient  non-nitrogenous  nutrients, 
has  sufficed  to  support  a  satisfactory  rate  of  fattening.  If  it 
appears  that  of  two  similar  animals  or  lots  of  animals  receiving 
equal  amounts  of  feed,  the  one  consuming  the  smaller  amount 
of  protein  gave  equally  satisfactory  gains,  both  as  judged  by 
the  live  weight  and  by  the  block  test,  it  may  be  concluded  that 
the  smaller  amount  of  protein  was  at  least  sufficient,  although 
it  cannot  be  determined  whether  it  may  not  have  been  greater 
than  was  actually  necessary. 

Unquestionably,  the  protein  requirements  of  mature  fatten- 
ing animals  have  been  greatly  overestimated  in  the  past.  Wolff's 
original  feeding  standards  (791),  published  in  1864,  recommended 
for  fattening  rations  per  thousand  pounds  live  weight  the  follow- 
ing amounts  of  digestible  protein :  — 

Cattle 2.5-3.0  Ib. 

Sheep 3-0-3-5  lb- 

Swine 2.7-5.0  lb. 

Substantially  these  same  figures  have  been  repeated  more 
or  less  uncritically  from  publication  to  publication,  with  a  few 
exceptions,  even  up  to  the  present  time.  It  is  clear,  however, 
from  Wolff's  writings  that  his  standards  were  based  upon  the 
then  prevailing  views  of  Voit  and  Pettenkofer  (248)  regarding 
the  importance  of  protein  as  a  source  of  animal  fat  rather  than 
upon  actual  experimental  results.  Subsequent  investigations, 
notably  the  respiration  experiments  of  Kellner  upon  cattle 
(p.  367),  have  fully  demonstrated  that  such  large  amounts  of 
protein  are  neither  necessary  nor  especially  advantageous  for 
fattening. 

Sheep.  —  Indeed,  Wolff  himself  has  demonstrated  that  his  protein 
standard  for  sheep  was  unnecessarily  high.  In  1890,  he  published  1 
the  results  of  a  comparison  made  in  1885-1886  of  maize  and  beans  as 
feed  for  fattening  sheep,  using  two  lots  of  two  mature  sheep  each. 
After  a  preliminary  feeding,  the  following  results  were  obtained  in 
107  days'  feeding :  — 

1  Landw.  Jahrb.,  19  (1890),  823. 


366 


NUTRITION  OF  FARM  ANIMALS 


TABLE  74.  —  INFLUENCE  OF  PROTEIN  SUPPLY  ON  GAIN  BY  MATURE  FAT- 
TENING SHEEP 


LOT  i,  FED 
ON  HAY 
AND  BEANS 

LOT  2,  FED 
ON  HAY 
AND  MAIZE 

Weight  at  beginning    
Weight  at  close  

Kgs. 

99-93 
118  71; 

Kgs. 
98.61 
118  56 

Gain  

1882 

IQ  Q^ 

Digestible  matter  eaten  per    1000  kilograms 
live  weight 
Protein    

3.26 

i  81 

Total  digestible  (fat  X  2  4) 

18  19 

in  20 

Lot  2,  receiving  maize,  produced  about  the  same  gain  relatively 
to  the  digestible  matter  consumed  as  Lot  i,  notwithstanding  the 
smaller  amount  of  protein  supplied.  A  block  test  tended  to  show  a 
slight  superiority  on  the  part  of  Lot  2.  Subsequent  experiments  l 
gave  confirmatory  results,  barley  being  compared  with  beans  on  one 
animal  each.  The  following  table  shows  the  actual  digestible  nu- 
trients, computed  per  1000  kilograms  live  weight,  and  the  total  gain 
for  each  period :  — 


TABLE  75.  —  INFLUENCE  OF  PROTEIN  SUPPLY  ON  GAIN  BY  MATURE  FAT- 
TENING SHEEP 


PERIOD 

NUMBER 
OF  DAYS 

SHEEP  No.  i,  FED  ON  BARLEY 

SHEEP  No.  2,  FED  ON  BEANS 

Total 
Gain 

Digested  per  1000 
Kilograms  Live 
Weight 

Total 
Gain 

Digested  per  1000 
Kilograms  Live 
Weight 

Protein 

Total 
Nutrients 

Protein 

Total 
Nutrients 

Kgs. 

Kgs. 

Kgs. 

Kgs. 

Kgs. 

Kgs. 

III  ... 
IV  ... 
V     .     .     . 

Total    . 

29 

20 

38 

1.6 
1.4 
4.0 

1.62 

1.63 
2.03 

14.69 

I5-23 
17.32 

2.4 
0.9 
3-6 

3-13 
2-95 
3-6l 

16.12 
16.02 
16.32 

7.0 

6.9 

1  Landw.  Jahrb.,  25  (1896),  175. 


THE  FATTENING  OF  MATURE  ANIMALS 


367 


In  the  final  period  of  an  experiment  by  Weiske  with  lambs  cited 
in 'Chapter  XI  (487)  the  animals,  when  two  years  old,  received  an 
exclusive  hay  ration  from  which  they  digested  1.22  Ib.  of  protein 
per  1000  pounds  live  weight.  While  no  material  fattening  was  pos- 
sible on  such  a  ration,  there  was  still  a  gain  of  protein  nearly  as  great 
per  head  as  in  earlier  periods,  thus  rendering  it  probable  that  the  pro- 
tein supply  was  at  least  nearly  sufficient  for  a  moderate  rate  of 
fattening. 

The  foregoing  results  indicate  that  1.5  Ib.  of  digestible  protein 
per  day  and  1000  pounds  live  weight  is  at  least  sufficient  for 
mature  fattening  sheep,  while  the  experiments  on  cattle  about  to  be 
mentioned  suggest  that  the  amount  might  even  be  reduced  consider- 
ably below  this  limit. 

Cattle.  —  In  Kellner's  respiration  experiments  upon  fattening 
cattle  (443) ,  rations  containing  comparatively  small  amounts  of  protein 
produced  as  satisfactory  a  rate  of  fattening  as  those  richer  in  that 
nutrient.  Dividing  the  experiments  into  five  groups  according  to 
the  amount  of  digestible  crude  protein  consumed  gives  the  following 
averages : — 

TABLE  76.  —  INFLUENCE  OF  PROTEIN  SUPPLY  ON  GAIN  BY  MATURE  FAT- 
TENING CATTLE 


RATIONS  PER  1000 

GAINS  PER  1000 

KGS.  LIVE  WEIGHT 

KGS.  LIVE  WEIGHT 

NUMBER 

.  AVER. 

GROUP 

LIVE 

MENTS 

WEIGHT 

Digestible 
Protein 

Metaboliz- 
able 
Energy 

Protein 

Fat 

Com- 
puted 
Energy 

Kgs. 

Kgs. 

Therms 

Grams 

Grams 

Therms 

I      ... 

7 

656 

0.523 

3J-54 

87.2 

6lO.I 

6.29 

II    ... 

14 

651 

o-745 

33.89 

82.3 

619.8 

6.36 

Ill  ... 

18 

667 

1.069 

34-50 

131.0 

661.0 

7-03 

IV  ... 

II 

67l 

1.332 

35.32 

154.0 

756.8 

8.07 

V     .     .     . 

IO 

691 

2.168 

43.36 

I57.0 

754-0 

8.06 

The  greater  gains  obtained  in  the  experiments  in  which  the  larger 
amounts  of  protein  were  fed  are  not  to  be  ascribed  to  this  fact  but  to 
the  greater  consumption  of  total  feed,  since  it  has  been  shown  that 
protein  is  no  more  available  than  non-nitrogenous  nutrients  for  fat 
production.  The  point  of  the  comparison  is  that  rations  containing 
amounts  of  protein  little  if  at  all  greater  than  the  maintenance  require- 
ment gave  relatively  quite  as  large  gains  per  unit  of  energy  supplied 
as  did  those  containing  three  or  four  times  as  much  protein. 


368 


NUTRITION  OF  FARM  ANIMALS 


The  periods  having  been  short  in  these  experiments,  the  gain  in 
live  weight  cannot  be  satisfactorily  determined,  but  on  the  basis  of 
Lawes  and  Gilbert's  determinations  of  the  composition  of  the  increase 
(442)  it  may  be  estimated  to  have  been  approximately  one  pound  per 
day. 

Loges  l  reports  the  results  of  experiments  undertaken  at  Pomritz 
to  test  Kellner's  conclusions,  in  which  a  nutritive  ratio  of  i :  10.3  gave 
as  great  gains  in  weight  with  mature  cattle  as  one  of  i :  5.7,  but  the 
absolute  amounts  of  protein  consumed  are  not  stated  in  the  abstract. 

Apparently  from  0.75  to  i  Ib.  of  digestible  protein  per  1000 
pounds  live  weight  is  sufficient  to  meet  the  requirements  of  fully 
mature  fattening  cattle. 

Swine.  —  Such  experiments  on  the  fattening  of  mature  swine  as 
are  on  record  show  that  these  animals,  like  cattle  and  sheep,  need  at 
most  but  a  comparatively  small  surplus  of  protein  over  the  amount 
necessary  for  maintenance. 

The  respiration  experiments  by  Meissl,  Strohmer  and  Lorenz  upon 
the  sources  of  fat  by  swine  (443)  afford  a  general  illustration  of  this. 
The  following  table  shows  the  digestible  protein  and  the  metaboliz- 
able  energy  of  the  feed  and  the  gain  of  energy  by  the  animal.  No 
distinct  superiority  of  the  high  protein  ration  of  Experiment  IV  over 
the  low  protein  rations  of  Experiments  I  and  III  appears,  while  the 
greatest  gain  was  realized  in  Experiment  II  with  a  moderate  protein 
supply  but  relatively  high  energy  content. 

TABLE  77.  —  INFLUENCE  OF  PROTEIN  SUPPLY  ON  GAIN  BY  MATURE  FAT- 
TENING SWINE 


RATIONS 
POUNDS  Li 

PER    100 

/E  WEIGHT 

GAIN  OF 

ENERGY 

ANIMAL 

LIVE 
WEIGHT 

Digestible 
Protein 

Metaboliz- 
able 
Energy 

Per  100  Lb. 
Live  Weight 

Per  Therm 
Metaboliz- 
able 
Energy 

I 

1  4O 

Lb. 

o  074. 

Therms 
r  ii 

Therms 

2    GA 

Therms 
O  ^O 

II       

7O 

o.  161 

IO.O2 

c  06 

o.q8 

Ill 

12  ^ 

o  098 

4IO 

I  4.8 

o  ^6 

IV           .     . 

IO4. 

o  4.10 

•2  04. 

2  <6 

O  43 

Soxhlet,  in  his  experiments  on  the  same  subject  (442) ,  fed  two  swine 
1 6  months  old  and  weighing  about  200  pounds  each  at  the  beginning 

1  Centbl.  Agr.  Chem.,  31  (1902),  646. 


THE  FATTENING  OF  MATURE  ANIMALS 


of  the  experiment,  a  low  protein  ration  consisting  exclusively  of  rice 
for  75  and  82  days,  respectively.  The  protein  content  of  the  ration 
and  the  average  daily  gain  in  live  weight  per  head  were  as  fol- 
lows :  — 

TABLE  78.  —  INFLUENCE  OF  PROTEIN  SUPPLY  ON  GAIN  BY  MATURE  FAT- 
TENING SWINE 


INITIAL  LIVE 
WEIGHT 

DIGESTIBLE  PROTEIN  (N  X  6.25) 

DAILY  GAIN 
IN  LIVE 
WEIGHT  PEK 
HEAD 

Per  Day  and 
Head 

Per  Day  and 
100  Lb.  Live 
Weight 

II 

Lb. 

220 

213 

Lb. 

0.265 
0.269 

Lb. 
O.I2I 
0.126 

Lb. 

I.I5 
1.04 

III    

These  few  results  upon  mature  swine  are  of  interest  as  showing  the 
possibility  of  considerable  fattening  on  low  protein  rations.  In  prac- 
tice the  results  are  of  comparatively  little  significance  since  the  com- 
mercial fattening  of  swine  is  usually  carried  out  upon  the  immature 
animal. 

The  recorded  experiments  show  that  in  the  fattening  of 
mature  animals  as  satisfactory  results  have  been  obtained  with 
rations  containing  0.75  to  1.5  pounds  of  digestible  protein  per 
1000  pounds  live  weight  as  with  those  containing  a  much  more 
abundant  supply.  Even  these  amounts,  however,  are  from 
50  to  100  per  cent  higher  than  is  necessary  for  maintenance, 
but  with  the  exception  of  a  small  group  of  Kellner's  experi- 
ments in  which  approximately  the  maintenance  requirement 
of  protein  was  consumed  the  results  fail  to  show  whether  it  is 
practicable  or  advisable  to  reduce  still  further  the  protein  con- 
tent of  fattening  rations.  As  regards  the  simple  question  of 
protein  supply,  it  appears  likely  that  an  amount  of  this  nutrient 
but  little  superior  to  the  maintenance  requirement  is  all  that  is 
absolutely  necessary.  In  practice,  however,  the  inferior  digesti- 
bility of  low-protein  rations  (723,  724)  as  well  as  the  fact  that 
such  rations  are  likely  to  be  less  palatable  than  those  furnishing 
a  more  liberal  supply  have  to  be  considered.  The  simple  ad- 
dition of  non-nitrogenous  nutrients  to  a  maintenance  ration 


370  NUTRITION  OF  FARM  ANIMALS 

might  furnish  ample  material  for  the  production  of  body  fat 
and  yet  not  convert  it  into  a  practicable  fattening  ration.  The 
economic  aspects  of  the  question,  however,  will  be  considered 
in  connection  with  the  subject  of  meat  production  (Chapter 
XII),  the  present  chapter  dealing  more  especially  with  the 
physiological  aspects  of  the  fattening  process. 


CHAPTER  XI 
GROWTH 

§  i.    GENERAL  NATURE  OF  GROWTH 

457.  Cell  multiplication.  —  The  animal  originates  in  a  single 
microscopic   germ   cell.     Its   advance   from   this   insignificant 
beginning  to  the  size  and  complexity  of  maturity  is~  effected 
by  a  multiplication  of  the  number  of  cells,  together  with  a 
progressive  differentiation  of  function,  the  whole  constituting 
the  process  of  growth.     Growth,  then,  may  be  characterized 
briefly  as  consisting  in  an  increase  of  the  structural  elements  of 
the  body,  chiefly  by  cell  multiplication,  resulting  in  a  gain  in  size 
and  weight. 

The  increase  during  growth 

458.  Composition  of  increase.  —  As  with  fattening  animals, 
so  in  a  study  of  the  feed  requirements  of  growing  animals,  a 
prime  factor  to  be  considered  is  the  amount  and  composition 
of  the  gain  made  at  different  ages.     The  nature  of  the  gain 
made  during  growth  may  be  investigated  either  by  means  of 
comparative  slaughter  tests  or  by  means  of  respiration  experi- 
ments.    Of  the  former  there  are  on  record  a  study  by  Wilson  l 
on  the  growth  of  pigs  for  the  first  16  days  after  birth,  an  inves- 
tigation by  Tschirwinsky  2  on  pigs  between  the  ages  of  2  and  6 
months,  one  by  Kern  and  Wattenberg  3  on  the  growth  of  lambs 
between  the  ages  of  6  and  28  months,  one  by  Jordan  4  upon  the 
growth  of  cattle  between  the  ages  of  23  and  33  months  and  one 
by  Wellmann  5  on  young  pigs.     Data  regarding  dogs  and  cats 
are  also  on  record  in  investigations  by  Thomas  6  and  by  Gerhartz.7 


1  Amer.  Jour.  Physiol.,  8  (1903),  197.  2  Landw.  Vers.  Stat.,  29  (1883), 

3  Jour.  Landw.,  28  (1880),  289. 

4  Maine  Expt.  Sta.,  Rpt.  1895,  Vol.  2,  pp.  36-77. 

5  Landw.  Jahrb.,  46  (1914),  499. 

6  Arch.  (Anat.  u.)  Physiol.,  1911,  p.  9. 

7  Arch.  Physiol.  (Pfliiger),  135  (1910),  163. 

371 


372 


NUTRITION  OF  FARM  ANIMALS 


Respiration  experiments  by  Soxhlet1  on  three  young  calves 
included  determinations  of  the  gain  or  loss  of  ash,  while  the 
live  weights  of  the  animals  are  also  recorded.  The  feed  being 
exclusively  milk,  the  variations  in  the  contents  of  the  digestive 
tract  were  probably  slight  and  a  computation  of  the  composition 
of  the  increase  based  upon  the  live  weights  seems  justified. 

The  results  of  both  the  slaughter  and  respiration  experiments 
are  contained  in  the  following  table,  the  energy  content  being 
computed  from  the  fat  and  protein. 

TABLE  79.  —  COMPOSITION  OF  INCREASE  OF  LIVE  WEIGHT  IN  GROWTH 


COMPOSITION  OF  INCREASE 

hr    t/5 

w  j5 

AUTHOR 

DESIGNATION  or 
ANIMAL  OR  PERIOD 

SPECIES 
OF  ANI- 
MAL 

AVER- 
AGE 
AGE 
DAYS 

Water 

Ash 

Pro- 
tein 

Fat 

Ot3 

|3 

w  S 

% 

% 

% 

% 

Cals. 

f 

Skim  milk                      1 

[ 

8 

80.08 

0.032 

18.40 

1.49 

540 

Wilson    .     .     .{ 

Lactose 

Swine  \ 

8 

78.91 

1.422 

17.92 

1-75 

529 

i 

Dextrose                        J 

( 

8 

79-44 

1.622 

17-30 

1.64 

5i8 

Wellman     .     .  J 

VIII                              1 
IX 

Swine  { 

37 
42 

75-53 
76.86 

1.92 

2.OO 

15-52  3 
15-  183 

7-03 
5-96 

698 
643 

I 

• 

4 

67.96 

1.84 

13-08  3 

17.12 

1055 

Thomas       .     . 



T\nr* 

16 

64.01 

2.52 

16.63  3 

16.84 

"Si 



LJQg 

54 

72.84 

2.89 

I7-593 

6.68 

736 

• 

101 

66.56 

4-49 

22.31  3 

6.64 

818 



4 

80.61 

1-63 

11.66  3 

6.10 

544 

Thomas      .     . 



Cat 

18 

68.29 

2-73 

18.93  3 

10.05 

935 



101  4 

64.16 

3-52 

24.01  3 

8.31 

982 

Gerhartz     .     . 



Dog 

IO 

72.93 

2.90 

13-98  3 

10.20 

800 

f 

C                                    1 

f 

8 

62.55 

3-35 

19.24 

14.86 

1136 

Soxhlet  .     .     .{ 

B.x 

Calf      \ 

IS 

61.28 

3-63 

19-15 

15-94 

1182 

I 

B.  2                                              J 

I 

21 

62.13 

3-50 

I7-I5 

17.22 

1186 

Tschirwinsky  .  ( 

No.  3                             \ 

Swine  < 

114 

46.51 

3-73 

9.10 

40.66 

1988 

I 

No.  2                            / 

I 

134 

34-23 

2.24 

9-73 

53-80 

2570 

Lot  I: 

Sheep 

Periods  I  and  II 

2QO 

43-84 

11.31  6 

44.85 

2226 

Periods  III  and  IV 

521 

27.27 

7-03  6 

65.70 

3014 

Kern  and  Wat- 

Period  V 

744 

22.18 

5.726 

72.IO 

3255 

tenberg    .     . 

Lot  II  : 

Sheep 

Periods  I  and  II 

290 

38.41 

9.91  6 

51-68 

2484 

Period  III 

458 

16.03 

4-13  6 

79.84 

3547 

Jordan  6      .     . 

Average 

Cattle 

840 

39.65  6.18 

13-57 

40.60 

2IOO 

1  ier  Ber.  Versuchs-Station  Wien,  pp.  101-155.  2  By  difference. 

3  Fat-  and  ash-free  dry  matter.  4  Two  periods. 

8  Computed  from  "  fat-free  body." 
6  The  figures  differ  slightly  from  those  reported  by  the  author. 


GROWTH 


373 


In  spite  of  irregularities  and  gaps  in  the  table  two  general 
facts  are  clearly  shown;  first,  that  the  percentage  of  water  in 
the  gain  decreases  and  that  of  dry  matter  increases  with  ad- 
vancing age  of  the  animal,  and  second,  that  of  the  dry  matter 
gained,  an  increasing  proportion  is  fat  as  the  animal  matures. 
The  latter  fact  becomes  especially  clear  if  the  composition  of 
the  dry  matter  of  the  ash-free  gain  be  computed. 

The  result  of  investigations  by  Waters,  Mumford  and  Trow- 
bridge  as  reported  by  Henry  and  Morrison  l  are  quite  in  accord 
with  the  teaching  of  Table  79,  the  percentage  composition  of 
the  first  and  the  second  500  pounds  gained  by  young  fattening 
steers  being  as  follows :  — 


WATER 

ASH 

PROTEIN 

FAT 

First  500  Ib  
Second  500  Ib. 

37°6 
17.8 

2.O 

11.9 

s-2  . 

48^6 

75- 

459.  Energy  content  of  gain.  —  The  amount  of  energy 
stored  in  a  unit  of  increase  in  live  weight  shows  a  fairly  regular 
and  notable  increase  as  the  animal  grows  older,  due  to  the 
smaller  percentage  of  water  and  the  higher  percentage  of  fat 
which  it  contains.  The  rate  of  increase  in  the  energy  content 
per  unit  in  those  cases  in  which  no  considerable  fattening  of  the 
animal  was  attempted  seems  to  be  fairly  regular  up  to  about  3.0 
Therms  per  pound  and  the  same  thing  is  also  true  of  most  of  the 
results  upon  fattening  animals  up  to  about  3.5  Therms  per 
pound,  although  the  actual  energy  content  per  unit  at  the  same 
age  is  naturally  greater  in  the  fattening  animal  and  the  limit  is 
therefore  reached  earlier  in  life.  In  both  cases  the  limit  seems  to 
correspond  in  a  general  way  with  the  average  energy  content  of 
the  gain  made  by  mature  fattening  animals  as  estimated  in 
Chapter  X  (451),  viz.,  about  3.25  Therms  per  pound.  The  data, 
however,  are  few  and  further  investigation  is  much  to  be  desired. 


Relation  of  growth  to  age 

460.   The  rate  of  growth.  —  If  the  successive  weights  or 
dimensions  of  a  growing  animal  be  platted,  there  are  obtained 
1  Feeds  and  Feeding,  isth  Ed.,  p.84. 


374  NUTRITION  OF  FARM  ANIMALS 

what  might  be  called  the  curves  of  weight  or  of  stature.  These 
rise  rapidly  at  first  and  afterwards  more  slowly  as  the  animal 
approaches  maturity.  Or  in  like  manner  the  increments  of 
weight  or  size  observed  in  successive  equal  periods  (day,  week, 
month  or  year)  may  be  platted,  showing  at  what  periods  the 
absolute  growth  is  most  rapid. 

It  is  evident,  however,  that  an  increase  of  a  pound  in  weight 
by  an  animal  weighing  500  pounds  is  relatively  much  less  than 
the  same  increase  in  a  loo-pound  animal.  For  many  purposes, 
a  better  expression  of  the  relation  of  growth  to  age  is  afforded 
by  a  computation  of  the  rate  of  growth,  by  which  is  meant  the 
increment  in  a  given  unit  of  time  expressed  as  a  fraction  of  the 
amount  present  at  the  beginning  of  that  time.  Thus  in  the 
instance  just  supposed  the  rate  of  growth  in  weight  per  day 
would' be  in  the  first  case  one  five-hundredth  and  in  the  second 
one  one-hundredth.  In  the  second  case  the  small  animal,  in 
proportion  to  its  weight,  is  growing  five  times  as  fast  as  the 
larger  and  may  be  regarded  as  showing  five  times  the  energy 
of  growth.  An  evident  advantage  of  this  manner  of  expression 
is  that  it  permits  of  a  comparison  between  animals  of  very  dif- 
ferent weights,  as,  for  example,  of  sheep  with  cattle. 

461.  Rate  of  growth  at  different  ages.  —  Somewhat  ex- 
tensive observations,  both  on  man  and  the  lower  animals,  show 
that  the  rate  of  growth  as  just  defined  diminishes  from  birth 
onward,  the  diminution  being  more  rapid  at  first  and  slower 
as  maturity  is  approached.  This  subject  has  been  discussed  in 
a  most  illuminating  manner  by  Minot 1  on  the  basis  of  his  own 
and  others'  observations  on  guinea  pigs,  rabbits,  chicks  and 
other  animals  as  well  as  on  man.  Graphically  the  rate  of 
growth  is  expressed  by  a  descending  curve,  steep  at  first,  but 
gradually  becoming  more  and  more  nearly  horizontal,  while 
the  same  curve  extends  backward  without  material  break 
into  intrauterine  life.  Foster  says:  "It  seems  as  if  the  im- 
petus to  growth  given  at  impregnation  gradually  dies  out."  In 
the  early  stages  of  growth,  therefore,  the  anabolic  processes, 
which  tend  to  build  up  tissue,  predominate,  while  as  time  goes 
on  the  katabolic  processes  gain  more  and  more  over  the 
anabolic  until  at  maturity  the  two  tend  to  become  substantially 
balanced. 

1 C.  S.  Minot :   Age,  Growth  and  Death,  Chapter  III. 


GROWTH  375 

462.  The   measure    of   growth.  —  The   most   familiar   and 
obvious  measure  of  growth  is  the  increase  in  size  or  weight  of 
the  body.     While  for  many  purposes  this  is  an  entirely  adequate 
standard,  it  is  not  a  strictly  accurate  expression  of  growth  proper. 

In  the  first  place  the  facts  regarding  the  composition  of  the 
increase  in  growth  which  have  just  been  considered  render  it 
evident  that  a  unit  of  gain  in  live  weight  has  a  very  varying 
significance.  In  the  very  young  animal  as  much  as  80  per  cent 
of  it  may  consist  of  water,  while  its  dry  matter  is  chiefly 
protein.  In  the  nearly  mature  animal,  on  the  contrary,  its 
percentage  of  water  may  fall  to  between  30  and  40,  while  its 
dry  matter  consists  largely  of  fat.  Moreover,  a  surplus  of  feed 
over  the  maintenance  ration  may  lead  to  a  deposition  of  fat 
in  the  young  as  well  as  in  the  mature  animal,  resulting  in  a 
greater  increase  in  weight  than  that  due  to  normal  growth. 
On  the  other  hand,  as  was  shown  in  Chapter  VIII  (372),  growth 
in  the  sense  of  increase  in  size  may  continue  on  a  ration  barely 
sufficient  or  even  insufficient  to  maintain  a  stationary  weight, 
i.e.,  growth  when  expressed  in  terms  of  weight  may  be  masked 
by  a  loss  of  fat. 

The  essential  structural  elements  of  the  body,  the  increase 
of  which  constitutes  growth  proper,  consist  (aside,  of  course, 
from  water)  mainly  of  protein  and  mineral  matter  (98).  Growth, 
therefore,  in  this  view  of  it,  is  equivalent  to  a  gain  by  the  body 
of  protein  and  ash,  especially  the  former.  The  increase  of 
protein,  therefore,  may  be  regarded  as  constituting  a  more 
accurate  measure  of  growth  in  the  narrower  sense  than  mere 
increase  in  weight. 

463.  Rate   of  increase   of  protein.  —  What  is   true  of  the 
weight  or  size  of  the  growing  animal  is  true  also  of  growth  in  the 
somewhat  narrower  sense  of  increase  of  protein  tissue. 

The  writer  has  elsewhere  1  collated  the  results  of  a  number 
of  experiments,  including  those  whose  results  regarding  the  com- 
position of  the  increase  are  recorded  in  Table  79,  in  which  the 
gain  of  protein  by  growing  animals  has  been  determined  with 
more  or  less  accuracy.  In  addition  the  results  of  experiments 
by  Fingerling  2  on  calves,  of  Ostertag  and  Zuntz  3  upon  pigs, 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  108  (1908),  pp.  13-17. 

2  Landw.  Vers.  Stat.,  68  (1908),  141 ;  76  (1912),  i. 
3Landw.  Jahrb.,  37  (1908),  231. 


376 


NUTRITION  OF  FARM  ANIMALS 


and  of  Just l  on  lambs  have  been  included  in  the  table  which 
follows. 

In  those  cases  in  which  the  experiments  were  made  by  the  method 
of  comparative  slaughter  tests,  the  composition  of  the  control  animals 
gives  an  approximate  measure  of  the  initial  protein  content  of  the 
body.  When  no  control  animal  was  analyzed  the  initial  protein  con- 
tent has  been  estimated  as  well  as  possible  from  the  live  weight. 
Since  this  was  the  case  in  the  majority  of  the  experiments  it  seems 
desirable  also  to  compute  the  gain  of  protein  per  1000  live  weight. 
Except  in  the  case  of  very  young  or  very  fat  animals,  the  results  are 
likely  to  correspond  substantially  with  those  computed  in  the  other 
way,  while  they  have  the  advantage  of  being  expressed  in  the  manner 
usually  adopted  for  formulating  feeding  requirements. 

TABLE  80.  —  RATE  OF  GAIN  OF  PROTEIN 


AVERAGE  AGE 
Days 


DAILY  GAIN  OF  PROTEIN 


Per  100  Body 
Protein 


Per  looo  Live 
Weight 


Cattle 

Soxhlet 8 

Soxhlet 15 

Soxhlet 18 

Soxhlet 21 

Fingerling 21 

Soxhlet 32 

De  Vries  Jzn       37 

De  Vries  Jzn 38 

Neumann 40 

Neumann 45 

De  Vries  Jzn 45 

Fingerling 47 

De  Vries  Jzn 50 

Neumann 50 

Neumann  ..." 54 

Neumann 57 

Neumann 62 

De  Vries  Jzn 63 

De  Vries  Jzn 64 

De  Vries  Jzn 65 

Fingerling 68 

Neumann 69 

De  Vries  Jzn 74 


2-347 
2.076 
1.644 
1.722 
1.974 
1.693 

'1-335 
1.246 

1-795 
1.449 
1.272 
1.248 
0.880 
1.082 
1.026 
1.320 

0-939 
0.678 

0.655 

1.020 

0.948 

1.062 

0.713 


3-994 
3-552 
2.803 
3.024 
3-085 
2-755 
2.276 
2.124 

2-945 
2.419 
2.169 
2.161 
1.500 
1.844 

2.284 
1.611 
1.209 
1.209 
1.723 
1.719 
1.823 
1.271 


1  Landw.  Vers.  Stat.,  69  (1908),  393,  results  of  periods  3,  5,  7  and  9. 


GROWTH 


377 


AVERAGE  AGE 
Days 


DAILY  GAIN  OF  PROTEIN 


Per  100  Body 
Protein 


Per  looo  Live 
Weight 


Cattle 

De  Vries  Jzn 100 

Fingerling 150 

Fingerling 182 

Fingerling 214 

Fingerling 297 

Jordan 840 

Sheep 

Weiske 140 

Weiske 177 

Weiske 214 

Weiske 254 

Just 285 

Kern  and  Wattenberg  ....  290 

Weiske 293 

Just 315 

Weiske 328 

Just 360 

Weiske 366 

Just 390 

Weiske 405 

Weiske 436 

Kern  and  Wattenberg  ....  458 

Kern  and  Wattenberg  ....  521 

Kern  and  Wattenberg  ....  745 

Swine 

Ostertag  and  Zuntz      ....  5! 

Sanford  and  Lusk 7 

Wilson 8 

Ostertag  and  Zuntz      ....  13 

Ostertag  and  Zuntz      ....  21 

Ostertag  and  Zuntz      ....  26 

Tschirwinsky 114 

Tschirwinsky 134 

Dog 

Thomas 4 

Gerhartz 10 

Thomas 16 

Thomas 54 

Thomas 101 

Cat 

Thomas 4 

Thomas 18 

Thomas  101 


0.711 
0.48 
0.41 
o-33 

0.22 
0.064 

0.372 
0.307 
O.2I9 
0.288 
0.233 
0.272 
0.179 
0.182 
O.I  60 
O.I  80 

0.238 
0.158 
0.178 

0-033 
0.068 

0.087 
0.067 

5-553 
7.269 
6.852 
4.129 
1.840 

0-757 
0.442 

0.483 

5-94 
6.44 
6.71 
1.70 
1.82 

6.10 

5-89 
i. 60 


1.192 
0.83 
0.76 
0.64 

o.47 
0.089 

0.651 

0-499 
0.360 
0.449 
0-475 
0.303 
0.284 
0.370 
0.264 
0.360 
0.382 

0.315 
0.301 
0.06 1 
0.074 
0.096 
0.069 

9.029 
5.621 

5-757 
6.675 

3-257 
1.470 
0.663 
0.740 

7-73 
7.67 
8-73 
2-35 
2-93 

7-57 
7.91 

3-05 


378  NUTRITION  OF  FARM  ANIMALS 

It  is  obvious  that  the  error  in  single  results  obtained  in  this 
way  may  be  very  considerable,  but  the  general  teaching  of  the 
table  is  perfectly  clear,  viz.,  that  the  rate  of  growth  of  protein 
tissue,  like  the  increase  in  size  or  in  weight,  whether  expressed 
per  unit  of  body  protein  or  per  1000  live  weight,  is  relatively 
high  in  the  new-born  animal  and  decreases  rapidly  at  first  and 
more  slowly  later,  tending  to  be  asymptotic  to  the  zero  line. 

Letting  the  g  equal  the  gain  of  protein  per  day  per  1000  live 
weight  and  a  the  age  in  days,  a  curve  represented  by  the  em- 
pirical equation  1 


corresponds  fairly  well  with  the  general  average  of  the  observed 
results  on  cattle  and  sheep.  With  swine,  the  few  results  ap- 
pear to  indicate  a  greater  rate  of  growth  during  the  first  three 
months.  This  is  shown  clearly  in  the  accompanying  graph 
(Fig.  38)  in  which  the  individual  results  on  the  different  species 
are  shown  by  the  light  lines,  while  the  heavy  curve  is  that  repre- 
sented by  the  foregoing  equation.  Of  course  considerable 
individual  variations  are  to  be  expected,  and  no  particular 
significance  attaches  to  the  mathematical  form  of  the  curve,  but 
it  would  seem  that  this  formula  may  be  used  tentatively  to 
express  in  a  broad  general  way  the  average  rate  of  protein 
growth  of  farm  ruminants  at  different  ages.  The  few  results 
on  the  dog  and  cat  seem  to  indicate  a  higher  rate  of  growth 
in  the  young  of  these  species. 

464.  Rate  of  gain  of  energy.  —  While  the  rate  of  increase 
of  protein,  as  discussed  in  the  foregoing  paragraphs,  may  be 
regarded  as  the  measure  of  growth  in  the  more  restricted  sense, 
and  while  it  is  of  importance  as  an  indication  of  the  amount  of 
protein  which  must  be  supplied  in  the  feed,  the  actual  gain  in 
normal  growth  includes  more  or  less  production  of  fat,  as  is 
clearly  shown  by  the  data  regarding  the  composition  of  the  in- 
crease already  considered  (458).  Growth,  therefore,  in  practice 
involves  a  storage  of  energy  in  the  body  not  merely  in  the  pro- 
tein gained  but  also  in  the  accompanying  fat  laid  on,  while  it 
is  difficult  to  draw  an  exact  line  between  the  growth  and  the 
fattening  of  young  animals. 

1  The  equation  of  a  rectangular  hyperbola. 


GROWTH 


379 


ill 


38o 


NUTRITION  OF  FARM  ANIMALS 


If  it  may  be  assumed  that  in  those  of  the  experiments  re- 
corded in  Table  79  in  which  no  considerable  fattening  was  at- 
tempted the  increase  in  weight  was  approximately  that  due  to 
normal  growth,  the  amount  of  energy  contained  in  the  increase 
and  the  daily  rate  of  gain  of  energy  per  1000  pounds  live 
weight  may  be  computed.  The  following  table  shows  the 
results  of  such  a  comparison,  the  figures  per  1000  pounds 
being  computed  in  direct  proportion  to  the  weight. 


TABLE  81.  —  ENERGY  CONTENT  OF  DAILY  GROWTH 


EXPERIMENTER 

ANIMAL 

AVERAGE 
AGE 

AVERAGE 
LIVE 
WEIGHT  * 

ENERGY  CONTENT 
OF  GROWTH 

Per  Head 

Penooo 
Lb.  Live 
Weight 

Thomas  
Thomas 

Dog 
Cat 
Pig  —  Average 
Calf 
Dog 
Calf 
Dog 
Cat 
Calf 
Pig 
Pig 
Dog 
Dog 
Cat 
Pig 
Pig 
Sheep,  Lot  I 
Sheep,  Lot  II 
Pig 
Sheep 
Sheep,  Lot  II 
Sheep,  Lot  I 
Sheep,  Lot  I 
Cattle 
Cattle 

Days 
4 
4 
8 
8 
10 

15 
16 
18 

21 
23 

34 

54 

101 
IOI 

114 

134 
290 
290 
300  1 
4561 
458 
521 
745 
840 
1460  l 

Lb. 
0.79 
0.38 
4.12 
106.87 
0.98 
138.60 

i-55 
0.864 

I5I-53 
I3-52 

jy-93 

3.38 

5-95 
1.91 

39-51 
34-66 
67.02 
73-42 
181.88 

135.58 
106.70 
102.51 
130.07 
826.10 
1272.40 

Cals. 
58.13 
14.67 

73-58 
2634.00 

49-3  1 
3i53.oo 
113.40 
39.20 
3294.00 
243-9 
316.5 
38.02 

73-°4 
27-34 
568.6 
705.6 
328.0 
608.  i 
5041.0 
1185.4 
712.9 

434-5 
520.4 
1618.0 
6378.0 

Therms 
73-35 
38.47 
17.87 
24.66 

50.47 
22.74 

73-35 
45.36 
21.74 
18.04 

17.65 
11.25 
12.28 
14.32 

14-39 
20.36 

4-90 
8.28 
27.72 

8-74 
6.68 

4-24 
4.00 
1.96 
5-oi 

Wilson 

Soxhlet  
Gerhartz 

Soxhlet 

Thomas 

Thomas 

Soxhlet 

Wellmann  .... 
Wellmann  .... 
Thomas  
Thomas 

Thomas    
Tschirwinsky     .     .     . 
Tschirwinsky     .     .     . 
Kern  and  Wattenberg 
Kern  and  Wattenberg 
Lawes  and  Gilbert 
Lawes  and  Gilbert 
Kern  and  Wattenberg 
Kern  and  Wattenberg 
Kern  and  Wattenberg 
Jordan       

Lawes  and  Gilbert 

1  Approximate. 


2  All  data  refer  to  empty  weight,  exclusive  of  hides. 


GROWTH  381 

The  rate  of  gain  of  energy  as  thus  computed  is  notably 
greater  for  young  carnivora  (dogs  and  cats)  during  the  first  two 
or  three  weeks  than  that  of  pigs  or  calves.  Aside  from  this,  the 
results  on  farm  animals,  although  more  or  less  irregular,  present 
in  general  the  same  picture  as  those  on  the  rate  of  gain  of  pro- 
tein, viz.,  a  diminishing  energy  of  growth  with  advancing  age. 
The  few  instances  showing  a  wide  divergence  from  the  majority 
may  probably  be  assumed  to  be  due  to  rapid  fattening. 

§  2.  THE  UTILIZATION  or  FEED  IN  GROWTH 

The  utilization  of  protein 

465.  Relative  values  of  proteins  for  growth.  —  A  considera- 
tion of  the  utilization  of  protein  in  growth  necessarily  raises 
the  question  of  the  relative  values  of  different  individual  pro- 
teins in  this  respect. 

As  was  pointed  out  in  Chapter  IX  (398),  it  appears  probable 
that  the  protein  requirement  for  maintenance  is  essentially 
an  amino  acid  requirement  and  that  the  relative  values  of 
proteins  for  maintenance  may  prove  to  depend  largely  or  wholly 
on  their  ability  to  supply  certain  specific  "  building  stones  " 
required  for  the  performance  of  specific  functions.  In  the 
growing  animal  there  is,  in  addition  to  this  requirement  for 
functional  purposes,  a  demand  for  amino  acids  out  of  which 
new  body  proteins  may  be  built  up.  In  growth,  therefore,  the 
amino  acid  requirements  may  differ  from  those  for  maintenance 
not  only  in  being  quantitatively  greater  but  in  being  qualita- 
tively different.  A  striking  illustration  of  this  is  afforded 
by  the  investigations  of  Osborne  and  Mendel l  on  the  relation 
of  lysin  to  growth. 

In  common  with  other  investigators  they  have  found  that  trypto- 
phan  is  indispensable  for  maintenance  (399).  Wheat  gliadin  con- 
tains tryptophan  but  only  a  minute  amount  of  lysin.  While  they 
have  repeatedly  secured  maintenance  for  long  periods  on  rations  con- 
taining gliadin  as  the  sole  protein,  they  have  been  unable  to  secure 
growth  with  such  rations,  but  the  simple  addition  of  lysin  enabled 
growth  to  proceed  at  a  normal  rate.  The  body  proteins  contain  lysin, 
ox  muscle,  for  example,  yielding  7.6  per  cent  (50).  Evidently  this 
1  Jour.  Biol.  Chem.,  12  (1912),  473;  17  (1913),  325;  86  (1916),  293. 


382  NUTRITION  OF  FARM  ANIMALS 

amino  acid  cannot  be  synthesized  in  the  body  but  must  be  supplied 
in  the  feed  in  order  to  permit  the  construction  of  the  new  protein 
molecules  in  the  tissue,  while  for  maintenance  (399)  it  appears  to  be 
dispensable.  Moreover,  they  have  shown  that  the  addition  to  in- 
adequate proteins  like  gliadin  of  other  proteins  containing  lysin  per- 
mits growth  to  take  place  and  furthermore  that  the  proportion  of  the 
second  protein  which  must  be  added  in  order  to  support  normal 
growth  is  less  in  proportion  as  it  is  richer  in  lysin. 

Osborne  and  Mendel's  conclusions  have  been  strikingly  confirmed 
by  the  results  obtained  by  Buckner,  Nollau  and  Kastle  l  from  feeding 
young  chicks  grain  mixtures  of  high  and  low  lysin  content. 

It  appears  that  the  lack  of  lysin  in  a  protein  renders  it  in- 
capable of  supporting  growth,  although  it  may  still  be  adequate 
for  maintenance  (399),  and  that  the  proportion  of  lysin  in  those 
proteins  containing  it  constitutes  a  limiting  factor  for  the 
amount  of  growth  which  they  can  support.  Tryptophan  is 
obviously  another  limiting  factor  in  this  respect,  while  it  must 
be  regarded  as  altogether  probable  that  other  amino  acids 
belong  in  the  same  category  and  may  become  limiting  factors 
if  the  supply  of  them  is  deficient.  In  other  words,  the  amount 
of  some  particular  amino  acid  which  is  available  may  become 
the  minimum  factor  which  determines  the  rate  of  growth,  just 
as  the  minimum  supply  of  potassium,  for  example,  may  deter- 
mine the  rate  of  growth  of  a  crop.  The  unsatisfactory  results 
obtained  in  practice  with  maize  as  the  sole  feed  for  young 
animals  may  well  be  due  in  large  part  to  the  poverty  of  the 
mixed  proteins  of  this  grain  in  tryptophan  and  lysin,  it  having 
been  shown  that  as  the  sole  source  of  protein  they  can  support 
but  slow  growth  (783). 

Unfortunately  the  knowledge  available  on  these  points  is  as 
yet  chiefly  qualitative  in  character  and  affords  no  sufficient 
foundation  on  which  to  base  a  quantitative  discussion  of  the 
relative  values  of  proteins  in  farm  practice.  Accordingly,  in 
the  case  of  growth  as  in  that  of  maintenance  it  appears  neces- 
sary for  the  present  to  consider  questions  regarding  the  protein 
requirement  upon  the  basis  of  total  protein,  largely  irrespective 
of  its  nature.  (Compare  Chapter  XVII,  §  4.) 

466.  Percentage  retention  of  feed  protein.  —  In  the  mature 
animal,  the  katabolism  of  protein  substantially  keeps  pace 

1  Amer.  Jour.  Physiol.,  39  (1915),  162. 


GROWTH 


383 


with  the  supply  in  the  feed  (402),  as  indeed  is  really  implied 
in  the  conception  of  maturity.  By  a  mature  animal  is  meant 
one  which  has  completed  its  growth,  and  growth  consists  essen- 
tially in  an  increase  of  the  nitrogenous  structural  elements 
of  the  body.  Obviously,  therefore,  if  the  capacity  for  growth 
has  been  exhausted,  no  material  storage  of  protein  can  occur 
and  an  excess  of  this  material  above  the  maintenance  require- 
ment will  serve  chiefly  or  wholly  as  a  source  of  energy  to  the 
organism. 

With  the  young  animal  the  case  is  different.  Its  rapidly 
growing  cells  and  tissues  demand  a  liberal  supply  of  protein, 
and  if  this  is  afforded  by  the  feed  it  is  largely  utilized  to  build 
up  tissue  instead  of  undergoing  nitrogen  cleavage.  Conse- 
quently, other  things  being  equal,  a  much  larger  percentage  of 
the  feed  protein  is  retained  in  the  body. 

The  investigations  whose  results  have  been  considered  on  previous 
pages  (463) ,  especially  those  upon  the  younger  animals,  afford  striking 
illustrations  of  this  fact,  Soxhlet's  experiments  upon  calves  being  the 
earliest  and  most  familiar.  Their  results  are  summarized  in  the  fol- 
lowing table,  the  feed  consisting  of  fresh  whole  milk  ad  libitum. 


TABLE  82.  —  PERCENTAGE  OF  FEED  PROTEIN  RETAINED  —  SOXHLET 


ANIMAL 

AGE 

DIGESTED 
PROTEIN 
OF  FEED 
PER  DAY 

DAILY 
GAIN  OF 
PROTEIN 
BY  ANIMAL 

DIGESTED 
PROTEIN 
RETAINED 

A 

Days 
1   i  6—  10 

Grams 
171   3 

Grams 

Per  Cent 

B       

30-33 

I  C 

1  /  *"6 
228.4 
330  8 

163.6 

231  8 

/b'6 

7i.6 

7O  I 

C      .     .     .     . 

21 

8 

317.5 
262  4 

216.1 

2O2  O 

68.1 

77  O 

More  recent  and  even  more  striking  illustrations  of  the  same  fact 
are  afforded  by  Fingerling's  experiments.  Thus,  in  one  instance 
a  calf  averaging  9  days  old  received  whole  milk  and  in  a  succeed- 
ing period  milk  with  the  addition  of  butter  fat  and  lactose,  and 
retained  the  percentages  of  digested  protein  shown  in  the  following 
table. 


384 


NUTRITION  OF  FARM  ANIMALS 


TABLE  83.  —  PERCENTAGE  OF  FEED  PROTEIN  RETAINED  —  FINGERLING 


PERIOD 

AGE 

(AVERAGE) 

DIGESTED 
PROTEIN 
OF  FEED 
PER  DAY 

DAILY 
GAIN  OF 
PROTEIN 
BY  ANIMAL 

DIGESTED 
PROTEIN 
RETAINED 

I        ....... 

Days 

Grams 
24.O  4.2 

Grams 
214.  38 

Per  Cent 
86  o 

II      .      . 

19 

254.94 

207.48 

81.4 

With  advancing  age,  a  relatively  smaller  retention  is  observed. 
Thus  Neumann  obtained  for  calves  40  to  70  days  old  percentages  vary- 
ing from  38.7  to  48.3,  and  Tschirwinsky,  experimenting  on  pigs  100 
to  120  days  old,  observed  a  retention  of  20.7  to  33.6  per  cent  of  the 
digested  protein.  With  still  older  animals  a  yet  smaller  percentage 
retention  has  been  observed,  diminishing  to  nearly  zero  with  fully 
mature  animals. 

467.  Does  not  measure  utilization.  —  On  the  basis  of  this 
greater  percentage  retention  it  has  been  customary  to  say  that 
the  utilization  of  feed  protein  is  high  in  the  case  of  the  young 
animal  and  diminishes  rather  rapidly  as  it  grows  older.     This 
statement  is  made  essentially  from  a  commercial  standpoint 
and  in  that  sense  it  is  true.     Only  the  growing  animal  is  capable 
of  using  any  large  amount  of  feed  protein  to  increase  its  stock 
of  body  protein  and  the  ability  to  do  this  is  the  more  marked 
the  younger  the  animal. 

The  percentage  retention  of  the  feed  protein,  however,  is 
necessarily  variable  and  neither  affords  a  measure  of  the  effi- 
ciency with  which  the  animal  converts  it  into  body  protein 
nor  permits  a  comparison  of  that  efficiency  at  different  ages. 
The  comparison  is  disturbed  by  two  important  factors  to  which 
attention  has  been  especially  called  by  Fingerling,1  viz.,  the 
influence  of  the  total  amount  of  protein  supplied  and  the  effect 
of  a  deficient  energy  supply. 

468.  Influence   of  protein   supply.  —  As   has  already  been 
implied,  growth  is  primarily  dependent  upon  biological  factors. 
The  feed  supplies  material  for  growth  but  does  not  determine 
its  maximum  rate.     The  rate  of  increase  of  protein  as  formu- 
lated in  the  previous  section  (463)  represents  (so  far  as  the 
results  are  trustworthy)  the  capacity  of  the  animal  for  protein 

1  Landw.  Vers.  Stat.,  74  (1910),  i. 


GROWTH 


385 


storage  at  different  ages,  but  the  percentage  of  the  feed  protein 
which  is  retained  will  depend  upon  the  relation  between  this 
capacity  and  the  amount  of  protein  actually  supplied.  For 
example,  suppose  a  calf  weighing  100  pounds  to  be  capable  of 
storing  up  per  day  0.25  pound  of  protein  and  to  require  0.05 
pound  for  maintenance.  If  it  receives  0.35  pound  digestible 
protein  in  its  feed  and  is  able  to  store  up  the  maximum  amount 
of  0.25  pound  on  this  ration,  71.4  per  cent  of  the  digestible 
protein  would  be  retained,  while  28.6  per  cent  would  katab- 
olize  and  its  nitrogen  excrete  in  the  urine.  But  if  the  feed 
of  the  animal  supplied  0.45  pound  digestible  protein,  the  gain 
would  still  be  0.25  pound,  since  this  is  the  maximum  possible 
for  the  animal,  but  the  percentage  of  the  feed  protein  retained 
would  be  only  55.6,  while  44.6  per  cent  of  it  would  be  katab- 
olized.  The  organism  is  unable  to  use  the  added  one-tenth 
pound  for  constructive  purposes  and  therefore  it  is  katabolized 
as  shown  in  Chapter  IX  (402-404)  and  serves  simply  as  a  source 
of  energy.  In  other  words,  the  greater  the  excess  of  protein 
supplied  in  the  ration  over  the  minimum  required  by  the  de- 
mands of  growth  and  maintenance,  the  lower  will  be  the  per- 
centage retained  in  the  body.  On  the  other  hand,  with  rations 
deficient  in  protein  the  percentage  retention  will  increase  with 
the  protein  supply  up  to  the  minimum  amount  necessary  to 
utilize  the  growth  capacity  of  the  animal. 

Fingerling's  experiments  afford  striking  confirmation  of  the  truth  of 
the  foregoing  deductions  from  the  general  laws  of  protein  katabolism. 

A  calf  received  daily  in  one  period  8  kgs.  of  whole  milk  with  an 
addition  of  butter  fat  and  lactose,  while  in  the  succeeding  period 
whole  milk  alone  was  fed  in  amounts  proportional  to  the  age  of  the 
calf,  averaging  11.875  kgs.  per  day.  The  results  as  regards  protein, 
expressed  in  terms  of  nitrogen,  were  as  follows :  — 

TABLE  84.  —  INFLUENCE  OF  PROTEIN  SUPPLY  ON  PERCENTAGE  RETENTION 

OF  NITROGEN 


DIGESTED 
NITROGEN 
OF  FEED 

URINARY 

NITROGEN 

GAIN  BY 
CALF 

PER  CENT 
OF  FEED 
PROTEIN 
RETAINED 

Grams 

Grains 

Grams 

June  2-5    
June  25-30    

42.49 
62.97 

7.91 
28.77 

34.58 
34.20 

81.4 
54-3 

2  C 


386 


NUTRITION  OF  FARM  ANIMALS 


Evidently  the  protein  supply  was  sufficient  in  the  first  period  to 
ensure  normal  growth.  The  additional  supply  in  the  second  period, 
therefore,  had  no  effect  on  the  gain  but  simply  increased  the  protein 
katabolism,  i.e.,  the  added  protein  was  used  as  a  source  of  energy  for 
maintenance  or  for  the  production  of  fat. 

On  the  other  hand,  a  supply  of  protein  notably  insufficient  to  per- 
mit normal  gain  may  yet  show  a  comparatively  high  percentage  re- 
tention. Thus  the  same  calf  received  in  an  intermediate  period  only 
4  kgs.  per  day  of  whole  milk  together  with  sufficient  butter  fat  and 
lactose  to  supply  the  necessary  energy.  As  compared  with  the  first 
period  only  about  one-half  of  the  normal  gain  of  protein  was  secured, 
yet  the  percentage  retention  is  but  slightly  reduced. 


TABLE  85.  —  HIGH  PERCENTAGE  RETENTION  OF  NITROGEN  ON  INSUFFI- 
CIENT PROTEIN 


DIGESTED 
NITROGEN 
OF  FEED 

URINARY 
NITROGEN 

GAIN  BY 
CALF 

PER  CENT 
OF  FEED 
RETAINED 

Tune  2—  t; 

Grams 
4.2  4.Q 

Grams 
7  OI 

Grams 

-1A    eg 

8l  4. 

June  13—18     ...          ... 

IQ.CK 

(ft 

14.00 

74.7 

469.  Influence  of  deficient  energy  supply.  —  But  not  only 
may  a  surplus  of  protein  be  utilized  as  a  source  of  energy  in  the 
manner  just  illustrated,  but  if  the  energy  supply  in  the  feed 
is  inadequate  protein  may  be  diverted  from  growth  to  serve 
as  fuel  material,  precisely  as  in  the  case  of  maintenance  (412), 
thus  lowering  both  the  observed  gain  and  the  percentage  re- 
tention. 

This  effect  is  well  illustrated  by  the  following  experiment  by  Fin- 
gerling  upon  a  calf  receiving  in  the  first  two  periods  a  limited  quan- 
tity (10  kgs.  per  day)  of  whole  milk.  As  the  animal  grew -older  the 
energy  supply  became  insufficient  and  protein  was  diverted  to  fuel 
purposes  so  that  the  actual  gain  and  the  percentage  retention  both 
diminished.  When,  in  a  third  period,  one-half  of  the  milk  was  re- 
placed by  butter  fat,  the  protein  supply  being  kept  at  nearly  the 
same  level  by  the  addition  of  egg  albumin,  the  actual  gain  rose  nearly 
to  its  original  level  and  the  percentage  retention  became  even  higher 
than  at  first  on  account  of  the  somewhat  reduced  protein  supply. 


GROWTH 


387 


TABLE  86.  —  INFLUENCE  OF  ENERGY  SUPPLY  ON  PERCENTAGE  RETENTION 
OF  NITROGEN 


DIGESTED 
NITROGEN 
or  FEED 

URINARY 
NITROGEN 

GAIN  BY 
CALF 

PER  CENT 
OF  FEED 
PEOTEIN 
RETAINED 

Grams 

Grams 

Grams 

Sept.  2g-Oct.  i  

51.84 

12.62 

39.22 

75-7 

Oct.  7-9    

5I-87 

19.99 

31.84 

61.5 

Oct.  19-27     

45-76 

8.10 

37-66 

82.3 

470.  Meaning  of  utilization.  — The  percentage  of  the  digest- 
ible protein  of  the  feed  which  is  retained  in  the  body  of  the 
growing  animal,  then,  is  not  in  itself  a  measure  of  the  efficiency 
of  the  animal  organism  in  converting  feed  protein  into  body 
protein,  since  the  proportion  retained  is  affected  both  by  the 
magnitude  of  the  protein  supply  in  the  feed  and  by  the  energy 
content  of  the  ration.  What  then  is  the  correct  conception  of 
the  utilization  of  the  feed  protein  ? 

As  appeared  in  the  previous  section,  the  amount  of  protein 
which  a  growing  animal  can  store  up  seems  to  be  a  function  of 
its  age  (463),  and  the  attempt  was  made  to  formulate  approxi- 
mately the  capacity  for  growth  in  this  sense  at  different  ages. 
The  percentage  utilization  of  the  feed  protein  in  the  physio- 
logical sense,  as  distinguished  from  the  percentage  retention,  is 
the  ratio  between  the  body  protein  thus  stored  up  and  the  least 
amount  of  feed  protein  in  excess  of  the  maintenance  require- 
ment which  is  necessary  to  support  this  growth  under  the  most 
favorable  conditions,  especially  as  to  energy  supply.  Suppose, 
for  example,  that  an  animal  three  months  old  actually  has  the 
capacity,  as  computed  by  the  formula  on  page  378,  to  store 
up  daily  1.23  pounds  protein  per  1000  pounds  live  weight,  and 
that  it  has  been  shown  that  it  can  just  reach  this  capacity  on 
a  ration  supplying  2  pounds  of  digestible  protein  per  day.  De- 
ducting 0.5  pound  for  maintenance  (415),  there  remains  1.5 
pounds  of  protein  in  the  ration  out  of  which  is  produced  1.23 
pounds  of  body  protein.  The  utilization  is  therefore  1.23  -5- 
1.5  =  82  per  cent.  If,  on  the  other  hand,  it  was  found  that 
2.5  pounds  of  protein  had  to  be  supplied  in  the  ration  in  order 


388 


NUTRITION  OF  FARM  ANIMALS 


to  bring  the  gain  of  protein  up  to  the  capacity  of  the  animal, 
the  percentage  utilization  would  be  only  1.23  -f-  2.0  =  62  per 
cent,  while  on  the  other  hand  if  the  maximum  growth  could 
be  secured  with  1.73  pounds  of  digestible  protein,  the  utili- 
zation would  evidently  be  100  per  cent. 

471.  Experimental  results.  —  The  writer  is  not  aware  of 
any  exact  determinations  of  the  percentage  utilization  in  the 
sense  just  denned,  that  is,  of  the  maximum  amount  of  protein 
tissue  which  can  be  produced  either  from  single  proteins  or  from 
the  mixed  proteins  of  feeding  stuffs,  but  interesting  data  regard- 
ing the  utilization  of  protein  by  growing  animals  are  furnished  in 
experiments  by  Fingerling  1  upon  calves  and  by  Just 2  on  lambs 
in  which  the  influence  of  a  varying  protein  supply  upon  the 
nitrogen  balance  was  determined. 

Reckoning  the  maintenance  requirement  for  protein  at  0.5 
pound  per  1000  pounds  live  weight,  Fingerling's  results  for  those 
periods  in  which  the  estimated  capacity  for  growth  appears  to 
have  been  fully  utilized  were  as  follows :  — 

TABLE  87.  —  COMPUTED  UTILIZATION  OF  PROTEIN  BY  CALVES 


GAIN  OF  PRO- 
TEIN PER 

FEED  PROTEIN 
IN  EXCESS  OF 
MAINTENANCE 

PERCENTAGE 
UTILIZATION 

AVER- 

PER   1000 

ANIMAL 

PERIOD 

AGE 
AGE 

DAYS 

Capac- 
ity  for 
Gain 

Ob- 
served 
Gain 

True 
Protein 

Crude 
Protein 

True 
Protein 

Crude 
Protein 

B.                   ./ 

i 

172 

0.70 

0.67 

1.94 

2.00 

34-5 

33-5 

I 

2 

175 

0.63 

0.63 

0.62 

0.84 

101.6 

75-o 

I 

157 

0.76 

0.85 

2.15 

2-44 

39-5 

34-8 

C                      . 

2 

184 

0.66 

0-75 

0.79 

1.04 

94-9 

72.1 

} 

( 

3 

211 

0.58 

0.68 

2-59 

2.85 

26.3 

23-9 

i 

237 

o-53 

0-57 

1.  08 

1.29 

52.8 

44.2 

G  

2 

262 

0.48 

0-54 

I-I3 

1-37 

47-8 

39-4 

4 

309 

0.41 

0.50 

0.3I 

0.49 

161.3 

IO2.O 

5 

339 

0.38 

0.44 

0.25 

0.42 

176.0 

IO4.8 

r 

Prelim- 

135 

0.87 

1.07 

2.42 

2.81 

44-2 

38.1 

H  

inary 

I 

1-6 

187 

0.05 

0.80 

0.74 

I.OI 

108.1 

79.2 

1  Landw.  Vers.  Stat.,  76  (1912),  i. 


Ibid.,  69  (1908),  393. 


GROWTH 


389 


From  these  figures  it  appears  that  in  the  low  protein  periods 
the  estimated  capacity  of  the  animals  for  growth  was  fully  uti- 
lized with  a  surplus  of  digestible  true  protein  over  the  maintenance 
requirement  equal  to  or  even  less  than  that  actually  recovered 
in  the  growth,  while  a  much  larger  supply  of  protein  failed  to 
secure  any  additional  growth  but  simply  forced  up  the  protein 
katabolism.  In  other  words,  if  the  estimate  for  the  maintenance 
requirement  is  approximately  correct,  the  utilization  of  the 
digestible  protein  in  the  low  protein  periods  must  have  ap- 
proached 100  per  cent.  Indeed,  in  at  least  two  cases  it  is  neces- 
sary to  admit  either  that  the  estimate  for  maintenance  is  too 
high  or  that  non-protein  was  used  for  maintenance. 

TABLE  88.  —  COMPUTED  UTILIZATION  OF  PROTEIN  BY  LAMBS 


FEED  PROTEIN 

AP- 

GAIN OF  PRO- 

IN  EXCESS  OF 

PERCENTAGE 

PROXI- 

TEIN PER  1000 

MAINTENANCE 

UTILIZATION 

o 

MATE 

PER    1000 

ANIMAL 

§ 

AVER- 

Pi 

AGE 
DAYS 

Capac- 
ity for 
Gain 

Ob- 
served 
Gain 

True 
Protein 

Crude 
Protein 

True 
Protein 

Crude 
Protein 

I 

262 

0.48 

O.OI 

—0.09 

O.O2 

— 

50.0 

2 

280 

o-45 

0.40 

0.17 

0-54 

235-3 

74.1 

3 

296 

o-43 

0.48 

0.42 

0.56 

II4-3 

85.7 

4 

310 

0.41 

0.16 

—0.14 

0.26 

— 

61.5 

I        

5 

324 

0-39 

0.36 

0.29 

0.44 

124.1 

8l.8 

6 

339 

0.38 

0.62 

0.27 

o-73 

229.6 

84.9 

7 

362 

0.36 

0.40 

0.38 

0.52. 

105-3 

76.9 

8 

377 

0-34 

0.24 

—  O.22 

0.23 

— 

104.3 

9 

391 

o-33 

0.34 

0.28 

0.42 

121.4 

81.0 

10 

407 

0.32 

-0.03 

—  0.21 

-O.II 

— 

—    . 

f   i 

262 

0.48 

o.oo 

—  O.II 

O.O2 



oo.o 

II      

280 

0-45 

0.32 

0.14 

o-49 

228.6 

65.3 

I   3 

296 

0-43 

0.47 

0.36 

0.52 

130.5 

90.4 

'   4 

310 

0.41 

0.07 

—  0.07 

0-37 

— 

18.9 

5 

324 

0-39 

0.38 

0.28 

0.42 

135-7 

90.5 

6 

339 

0.38 

0.61 

O.2I 

0.63 

290.5 

96.8 

Ill  x       .... 

<     7 

362 

0.36 

0-33 

O.42 

o-57 

78.6 

57.9 

8 

377 

0.34 

0.24 

—  O.22 

0.24 

— 

IOO.O 

9 

391 

0-33 

0.29 

0.25 

0.41 

116.0 

70.7 

10 

407 

0.32 

o.oo 

—  O.2O 

-0.08 

— 

— 

1  Substituted  for  No.  II. 


3QO  NUTRITION  OF  FARM   ANIMALS 

Interesting  data  pointing  in  the  same  direction  are  contained 
in  the  investigation  by  Just,  in  which  the  nutritive  value  of 
non-protein  for  lambs  was  compared  with  that  of  protein. 
Estimating  the  maintenance  requirement  at  0.5  per  thousand 
and  computing  the  results  of  the  protein  periods  as  in  Finger- 
ling's  experiments,  it  appears  that  in  nearly  every  case  the 
actual  gain  of  protein  was  only  slightly  less  than  the  surplus  of 
digestible  crude  protein  above  the  maintenance  requirement, 
while  in  many  cases  it  was  distinctly  greater  than  the  digestible 
true  protein  available.  Apparently  the  non-protein  must  at 
least  have  contributed  to  the  maintenance  of  the  animal  if  not 
to  its  growth,  while  the  utilization  of  the  digestible  true  protein 
must  have  been  very  high  (Table  88). 

Neither  Fingerling's  nor  Just's  investigations  are  adequate 
to  solve  the  general  problem  of  the  maximum  possible  utiliza- 
tion of  protein  in  growth,  but  their  results  indicate  that  it  may 
be  very  high  and  should  lead  to  caution  in  the  interpretation  of 
experiments  upon  the  protein  requirements  for  growth. 

Utilization  of  energy  —  net  energy  values  for  growth 

472.  General  conception.  —  The  conception  of  net  energy 
values  for  growth  is  entirely  analogous  to  that  of  net  energy 
values  for  maintenance  or  for  fattening.  They  represent  that 
portion  of  the  feed  energy  supplied  in  excess  of  the  maintenance 
requirement  which  the  animal  is  able  to  store  up  in  the  gain 
made.  It  is  important  to  keep  this  conception  clearly  in  mind 
when  considering  the  utilization  of  feed  in  growth  and  not  to 
be  misled  by  the  greater  economic  efficiency  of  the  young  animal 
as  a  producer  of  live  weight  increase. 

It  is  a  familiar  fact  that  the  young  animal  gains  in  weight 
relatively  much  faster  than  when  more  mature  and  this  has 
led  to  the  general  impression  that  the  young  animal  utilizes  its 
feed  more  perfectly  than  the  older  animal,  or  in  other  words, 
that  the  net  energy  value  of  a  feeding  stuff  for  growth  is  greater 
than  that  for  maintenance  or  for  fattening.  It  is  true  that  the 
gain  in  live  weight  is  different  in  character  in  the  young  animal, 
containing  more  water  and  protein  and  less  fat  and  therefore 
less  energy  (458,  459) ,  but  on  the  other  hand  the  results  recorded 
in  §  i  show  a  greater  rate  of  growth  as  regards  both  protein  and 


GROWTH  391 

energy  (463,  464)  in  the  young  animal  as  compared  with  the 
more  mature  one.  Is  this  difference  to  be  ascribed  to  a  specif- 
ically higher  percentage  utilization  on  the  part  of  the  younger 
animal,  or  is  it  due  to  a  relatively  greater  consumption  of  feed 
or  the  relatively  high  net  energy  values  which  usually  char- 
acterize the  feeds  given  the  young  animal,  particularly  milk? 
The  mere  fact,  for  example,  that  a  young  animal  consuming 
milk  utilized  a  higher  percentage  of  the  feed  energy  than  did 
the  same  animal  later  upon  a  mixed  ration  would  not  necessarily 
show  any  physiological  superiority  on  the  part  of  the  younger 
animal  but  might  be  due  solely  to  the  difference  in  the  kind 
of  feed  consumed.  So,  too,  the  mere  ability  to  consume 
relatively  large  amounts  of  highly  concentrated  feed  in  the 
form  of  milk  and  thus  to  secure  a  large  surplus  above  the 
maintenance  requirement  might  (360,  510)  give  the  younger 
animal  a  marked  economic  advantage  without  indicating  any 
more  efficient  conversion  of  the  surplus  energy  supplied  than 
in  the  older  animal. 

Unfortunately,  investigations  regarding  the  utilization  of 
feed  at  different  ages  have  been  few  in  number  and  the  avail- 
able data  regarding  net  energy  values  for  growth  are  exceed- 
ingly meager.  To  a  large  extent  it  is  necessary  to  be  content 
with  comparisons  of  a  very  general  nature,  leading  to  proba- 
bilities only. 

473.  Experiments  on  suckling  animals.  —  The  experiments 
by  Soxhlet  on  calves  and  those  by  Wilson  on  pigs  cited  on 
previous  pages  (458)  and  likewise  an  investigation  by  Rubner 
and  Haubner  1  on  infants  afford  some  data  for  approximate 
estimates  of  the  percentage  of  the  metabolizable  energy  of  milk 
utilized  by  growing  animals. 

The  computations  involve  a  number  of  uncertain  assump- 
tions, particularly  as  regards  the  maintenance  requirement, 
and  none  of  them  afford  a  satisfactory  basis  for  comparing 
the  utilization  of  the  metabolizable  energy  of  milk  at  different 
ages.  It  is  of  some  interest,  however,  to  compare  the  average 
utilization  computed  from  these  experiments  with  that  esti- 
mated by  the  use  of  Rubner's  factors  for  the  "  specific 
dynamic  action  "  of  equal  amounts  of  pure  nutrients  on  mature 
animals. 

lZtschr.  Biol.,  36  (1898),  i ;  38  (1899),  315. 


392 


NUTRITION  OF  FARM  ANIMALS 


As  explained  in  Chapters  VIII  and  XVII  (366,  759),  Rubner's 
"specific  dynamic  action"  is  synonymous  with  the  energy  expendi- 
ture caused  by  the  consumption  of  feed,  and  if  it  be  subtracted  from 
the  metabolizable  energy  the  remainder  is  the  net  energy.  The  per- 
centage utilization  is  of  course  the  net  energy  divided  by  the  metab- 
olizable energy. 

Estimated  in  this  way,  the  percentage  utilization  would  be 
as  shown  in  the  first  column  of  the  following  table,  the  second 
and  third  columns  of  which  show  the  utilization  as  computed 
by  the  writer  both  with  and  without  a  10  per  cent  addition  to 
the  fasting  katabolism  as  estimated  from  the  data  on  mature 
animals. 


TABLE   89.  —  ESTIMATED  UTILIZATION   OF   METABOLIZABLE   ENERGY   OF 

MILK 


COMPUTED 

BY  WRITER 

COMPUTED, 

USING 
RUBNER'S 
FACTORS 

Fasting 
Katabolism 
Same  as  in 
Mature 
Animals 

Fasting 
Katabolism 
10% 
Greater 
than  in 
Mature 
Animals 

Rubner's  experiments 

84  08 

% 

Soxhlet's  experiments 

86  18 

73  77 

7?  ?6 

Wilson's  experiments      

83.99 

70.31 

75-47 

While  it  is  clear  that  no  final  conclusions  can  be  based  upon 
small  differences  between  figures  obtained  as  these  have  been, 
it  seems  suggestive,  nevertheless,  that  the  actual  experiments 
with  growing  animals  show  a  lower  average  utilization  than 
would  be  expected  from  Rubner's  results  upon  mature  animals. 
Moreover,  Wilson's  results  are  apparently  lower  than  those 
which  may  be  computed  from  Meissl's  and  Kornauth  and 
Arche's  respiration  experiments  upon  mature  swine  consuming 
grain  (757).  Certainly  these  comparisons  afford  little  sup- 
port to  the  notion  that  the  utilization  of  energy  in  the  physio- 
logical sense  by  young  animals  is  much  higher  than  that  by 
mature  animals. 


GROWTH  393 

474.  Experiments  on  older  animals.  —  Of  experiments  upon 
older  animals  those  of  Kern  and  Wattenberg  on  lambs  and  of 
Tschirwinsky  on  pigs  (458),  permit  an  approximate  computa- 
tion of  the  utilization  of  the  feed  energy  during  growth  and 
afford  data  for  some  comparisons,  although  in  neither  case 
were  very  young  animals  employed,  the  lambs  being  between 
6  and  7  months  old  at  the  beginning  of  the  experiment  and  the 
pigs  between  9  and  10  weeks. 

On  the  whole,  the  results  of  these  experiments  seem  to  indi- 
cate, if  anything,  a  rather  lower  percentage  utilization  by  the 
younger  animals  as  compared  with  the  older.  At  any  rate  they 
fail  to  show  any  superiority  on  the  part  of  the  former.  The  same 
is  true  of  the  results  of  experiments  by  Armsby  and  Fries *  upon 
steers  10  to  27  months  old  in  which  the  availability  was  deter- 
mined by  the  use  of  the  respiration  calorimeter.  While  not  de- 
cisive, the  results  seem  to  indicate  a  slightly  lower  availability  of 
the  mixed  grain  and  possibly  of  the  hay  for  the  younger  animals. 

475.  Embryonic  growth.  —  Several  experimenters,  especially 
Tangl  and  his  associates  2  and  Bohr  and  Hasselbalch,3  have 
determined  the  energy  expended  in  the  development  of  the 
embryo  in  oviparous  animals,  i.e.,  in  the  organization  of  the 
substances  of  the  egg  into  embryonic  tissue.     These  investi- 
gations have  shown  that  a  relatively  large  proportion  of  the 
chemical  energy  contained  in  the  egg  is  evolved  as  heat  during 
the  process  of  development,  so  that  the  percentage  recovered 
in  the  embryo,  ranging  from  60  to  68  per  cent,  is  distinctly 
lower  than  the  utilization  of  the  energy  of  milk  by  suckling 
animals  as  computed  in  a  previous  paragraph  (473).     More- 
over, they  show  that  the  utilization  of  the  energy  of  the  egg  is 
notably  less  in  the  earlier  than  in  the  later  stages  of  incubation, 
as  low  a  figure  as  28  per  cent  having  been  observed  after  10 
days'  incubation. 

The  method  may  be  illustrated  by  the  results  of  two  experiments 
by  Tangl  and  Mituch,  each  upon  three  hens'  eggs.  From  analyses  of 
similar  eggs  from  the  same  hen,  it  was  computed  that  the  three  used 
contained  respectively  229.72  Cals.  and  291.38  Cals.  chemical  energy. 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  128  (1911),  51. 

2  Arch.  Physiol.  (Pfliiger),  93  (1903),  327  ;  98  (1903),  490;  104  (1904),  624;  121 
(1908),  423  and  437. 

3  Skand.  Arch.  Physiol.,  10  (1900),  149  and  353 ;  14  (1903),  398. 


394 


NUTRITION  OF   FARM  ANIMALS 


At  the  end  of  incubation  the  embryo  *  was  separated  from  the  yolk 
sack  and  its  contents  and  the  energy  of  each  determined  with  the  fol- 
lowing results :  — 

TABLE  90.  —  UTILIZATION  OF  ENERGY  IN  INCUBATION 


EGGS  PROM 
HEN  VIII 

EGGS  FROM 
HEN  X 

Original  energy  of  eggs  

229.72  Cals. 

291.38  Cals 

Remaining  in  yolk  sack  and  contents  .  .  . 

63.95  Cals. 

94.64  Cals. 

Used  for  production  of  embryo  
Recovered  in  embryo  
Percentage  recovered  .  .  . 

165.77  Cals. 
99.24  Cals. 
59.87  Cals. 

196.74  Cals. 
125.66  Cals. 
63.84  Cals 

In  other  words,  35  to  40  per  cent  of  the  energy  of  the  egg  substance 
used  was  not  recovered  but  escaped  as  heat.  Comparison  with  the 
loss  of  dry  matter  showed  that  the  material  thus  katabolized  consisted 
substantially  of  fat.  No  loss  of  nitrogen  was  observed. 

Experiments  on  mammalian  and  reptilian  embryos,  especially 
by  Bohr,2  by  Murlin  3  and  by  Carpenter  and  Murlin,4  appear  in 
accord  with  the  foregoing  conclusion,  since  they  show  that  the 
metabolism  of  the  embryo  per  unit  of  weight  is  as  great  or 
greater  than  that  of  the  mature  animal,  despite  the  fact  that  the 
maintenance  requirement  of  the  former  must  be  decidedly  less. 

The  growth  of  the  embryo  consists  essentially  of  the  organ- 
ization of  protein  tissue.  The  fact  that  there  is  no  loss  of  nitro- 
gen during  incubation  would  indicate  that  chemically  the 
process  is  effected  by  a  cleavage  and  resynthesis  of  protein 
which  appears  to  be  a  nearly  iso thermic  process  (233,  367  d). 
Apparently  the  organization  of  the  protein  into  structure  is 
what  calls  for  the  large  expenditure  of  energy. 

476.  Summary.  —  The  experimental  results  mentioned  in  the 
foregoing  paragraphs  may  be  briefly  summarized  in  the  follow- 
ing statements :  — 

In  the  case  of  suckling  animals,  while  no  direct  comparisons 
of  the  same  animal  at  different  ages  are  available,  the  utilization 
of  the  metabolizable  energy  of  milk  for  growth  appears  to  be 

1  Including  the  egg  membranes. 

2  Skand.  Arch.  Physiol.,  10  (1900),  413  ;  15  (1904),  23. 

3Amer.  Jour.  Physiol. ,  26  (1910),  134.  4  Arch.  Inter.  Med.,  7  (1911),  184. 


GROWTH  395 

distinctly  less  than  would  be  expected  from  Rubner's  results 
on  the  utilization  of  pure  nutrients  by  mature  animals.  In  the 
case  of  swine,  moreover,  the  utilization  appears  to  be  even  less 
than  that  of  the  metabolizable  energy  of  grain  by  mature  ani- 
mals, although  the  contrary  would  naturally  have  been  antici- 
pated. The  results  with  older  animals,  while  far  from  conclusive, 
seem,  if  anything,  to  indicate  a  lower  utilization  by  younger 
animals  as  compared  with  older  ones  and  at  any  rate  fail  to 
show  that  it  is  any  greater  in  the  former  case. 

The  results  on  embryonic  growth  show  a  relatively  large 
expenditure  of  energy  in  development  and  indicate  a  compara- 
tively low  utilization  of  energy.  This  large  expenditure  of 
energy  in  development  seems  to  be  required  chiefly  for  the 
organization,  in  the  broader  sense,  of  the  embryonic  structure 
rather  than  for  the  mere  chemical  transformation  of  egg  sub- 
stances, and  it  seems  to  be  relatively  greater  in  the  young  as 
compared  with  the  more  mature  embryo. 

477.  Provisional  hypothesis.  —  While  it  would  be  rash  to 
draw  any  final  conclusions  from  the  foregoing  data,  it  may  be 
permissible  to  formulate  a  working  hypothesis  to  the  effect 
that  the  conversion  of  feed  protein  (including  the  protein  of 
the  egg)  into  tissue  requires  a  considerably  greater  relative 
expenditure  of  energy  than  does  the  conversion  of  surplus  feed 
into  fat,  the  difference  representing  what  might  be  called  the 
work  of  organization,  i.e.,  the  formation  of  organized  structure 
in  the  young  animal  and  especially  in  the  embryo.  It  has 
been  shown  (463)  that  the  rate  of  growth  decreases  rapidly 
with  increasing  age.  Accordingly,  the  work  of  organizing  new 
protein  tissue,  so  far  as  this  is  measured  by  the  storage  of  pro- 
tein, must  constitute  a  steadily  diminishing  proportion  of  the 
total  energy  expenditure  of  the  organism,  since  as  the  animal 
grows  older  the  increase  consists  to  a  diminishing  extent  of 
protein  and  to  an  increasing  extent  of  fat.  The  percentage 
utilization  of  the  feed  energy  would  therefore,  upon  this  hypothe- 
sis, tend  to  increase.  It  would  be  least  immediately  after  birth 
and  after  two  to  four  months  would  become  relatively  small, 
corresponding  to  the  changing  character  of  the  gain.  Probably 
by  the  time  an  animal  has  been  weaned  and  is  consuming  the 
normal  feed  of  its  species,  the  percentage  utilization  of  the  feed 
energy  might  be  assumed  to  be  not  much  less  than  that  ex- 


396  NUTRITION  OF  FARM  ANIMALS 

hibited  by  the  mature  animal  and  at  any  rate  to  be  practically 
proportional  to  it.  This  would  mean,  of  course,  that  the  net 
energy  values  of  feeding  stuffs  for  maintenance  and  fattening 
might  be  used  also  to  measure  at  least  their  relative  if  not  their 
absolute  net  energy  values  for  growing  animals. 

The  determination  of  the  validity  of  this  provisional  con- 
clusion offers  an  interesting  and  profitable  field  for  investigation. 

§  3.   THE  FEED  REQUIREMENTS  FOR  GROWTH 

478.  Contrast  with  fattening.  —  la  the  case  of  fattening 
animals  the  conception  of  the  feed  requirement,  particularly  as 
regards  energy,  is  somewhat  artificial,  since  the  extent  of  the 
fattening  depends,  within  the  limits  of  the  animal's  capacity, 
largely  upon  the  amount  of  feed  supplied.  Growth,  on  the 
other  hand,  unless  the  feed  fails  to  supply  the  necessary  materials 
and  thus  becomes  a  limiting  factor,  goes  on  at  a  rate  substan- 
tially determined  by  other  conditions,  the  most  obvious  of 
which  are  the  species,  individuality  and  age  of  the  animal. 
Indeed,  it  may  be  said  that,  within  normal  limits,  the  capacity 
for  growth  determines  the  feed  consumption  rather  than  the 
reverse.  Heavy  feeding  may  cause  fattening  but  it  does  not 
appear,  at  least  in  the  case  of  the  higher  animals,  to  materially 
accelerate  growth,  although  Eckles  1  observed  the  growth  of 
dairy  calves  to  be  somewhat  more  rapid  upon  heavy  as  com- 
pared with  scant  rations.  In  growth,  therefore,  as  in  mainte- 
nance, there  is  a  real  requirement  to  be  satisfied,  its  measure  be- 
ing the  amount  and  character  of  th6  increase  which  the  young 
animal  is  capable  of  making  under  normal  conditions. 

Mention  has  been  made  (372)  of  the  interesting  results  of  experi- 
ments by  Waters  2  upon  growth  under  adverse  conditions,  while 
Osborne  and  Mendel 3  have  shown  that  growth  which  has  been  sus- 
pended for  a  time  because  of  inadequate  feed  supply  may  be  resumed 
when  this  deficiency  is  made  good  (deferred  growth).  Neither  of 
these  possibilities,  however,  invalidates  the  statement  just  made  that 
the  continued  maintenance  of  a  normal  rate  of  growth  requires  a 
definite  supply  of  matter  and  energy. 

1  Mo.  Expt.  Sta.,  Bui.  135,  1915. 

2  Soc.  Prom.  Agr.  Science,  Proc.  2gih  Annual  Meeting,  1908,  p.  71. 

3  Jour.  Biol.  Chem.,  18  (1914),  195;  23  (1915),  439;   Amer.  Jour.  Physiol.,  40 
(1916),  16. 


GROWTH 


397 


479.   Total  increase  in  normal  growth  at  different  ages.  — 

The  feed  requirements  of  the  growing  animal  as  regards  protein 
and  energy  depend  in  the  first  place  on  the  amounts  which  such 
an  animal  is  capable  of  storing  up  in  normal  growth.  From  the 
data  regarding  the  rate  of  growth  recorded  in  §  i  of  this  chapter, 
even  though  they  are  somewhat  fragmentary,  it  seems  possible  to 
derive  average  figures  regarding  the  storage  of  protein  and  energy 
in  growth  at  different  ages  which  may  be  of  some  value  as  a  guide 
in  estimating  the  feed  requirements  of  the  growing  animal. 

As  regards  protein,  it  was  shown  that  the  rate  of  gain  per 
1000  live  weight  apparently  does  not  vary  widely  as  between 
cattle,  sheep  and  swine,  and  an  empirical  formula  (463)  was 
given  by  which  its  amount  at  any  age  may  be  approximately 
estimated.  As  regards  energy,  fewer  data  are  available,  es- 
pecially for  farm  animals,  but  the  graphic  representation  in  Fig. 
39  of  the  results  recorded  in  Table  81  (464)  shows  a  diminish- 
ing rate  of  gain  of  energy  as  the  animal  grows  older. 

In  the  following  tabulation  the  daily  gain  of  protein  at  differ- 
ent ages  has  been  calculated  by  means  of  the  formula  just  men- 
tioned and  the  gain  of  energy  estimated  from  the  smoothed  graph 
of  Fig.  39.  The  two  together  may  be  taken  as  an  approximate 
expression  of  the  normal  increase  in  growth  at  different  ages. 

TABLE  91.  —  DAILY  INCREASE  IN  GROWTH  PER  1000  POUNDS  LIVE  WEIGHT 


AGE 

PROTEIN 

ENERGY 

4* 

10  days 

Pounds 
4^O 

Therms 

24.  S 

20  days     .  .        .      .        . 

3.^8 

21  8 

30  days 

2.70 

2O.O 

60  days 

I  ^O 

16  o 

QO  days 

1.23 

J5  O 

1  20  days   

0.96 

1  1.5 

i  <^o  davs 

O  7Q 

10  o 

180  days   

0.68 

o.o 

210  days 

O  ^O 

8  <; 

240  days   ...        .            . 

O  ^2 

7  S 

270  days   

O.47 

7.O 

300  davs 

O  4.2 

6  <? 

i  year   

O  1$ 

C.C 

ji  years 

O  24 

A  O 

2^  vears 

O  IS 

2.C 

398 


NUTRITION  OF  FARM  ANIMALS 


ifc 


\ 


\ 


\ 


\ 


\ 


\ 


a 
ll 

Q    ° 
I1 'I 


Therms  per  1000 
pounds  live  weight 


GROWTH  399 

Energy  requirements 

480.  Computation    from    daily    increase.  —  The    estimates 
contained   in  the  foregoing   table  of   the  amount  of   energy 
stored  up  in  growth,  although  unfortunately  based  on  scanty 
data,    show,  to  the  extent  to  which  they  can  be  relied   on, 
the   amounts  of    net    energy   which    are    necessary   for    the 
support     of     growth    without     any     considerable     fattening. 
Since   the  results  described  in   §  2   render  it  probable  that 
the  net   energy   values  of   feeding  stuffs  for  growth  do  not 
differ  widely  from  those  for  maintenance  or  for  fattening  (477), 
the  figures  of  the  table,  with  the  addition  of  the  maintenance 
requirement,  would  afford  a  basis  for  computing  rations  for 
young  animals. 

481.  Computation    from    gain    in    live    weight.  —  Another 
method  of  computation  furnishes  to  a  certain  degree  a  check 
upon  the  results  recorded  in  the  last  table.     The  amount  of 
energy  stored  up  in  the  increase  at  different  ages  may  be  esti- 
mated by  applying  the  results  regarding  the  energy  values  per 
unit  of  increase  which  are  recorded  in  Table  79  (458)  to  the  gain 
of  live  weight  actually  observed  in  the  growth  of  animals  under 
normal  conditions. 

a.  Cattle.  —  From  data  secured  at  the  Missouri  Experiment 
Station  l  regarding  the  rate  of  growth  of  5  Hereford,  6  Jersey, 
2  Ayreshire  and  5  Holstein  calves,  the  writer  has  computed 
the  following  figures  for  the  daily  gain  of  energy  per  1000  pounds 
live  weight  by  calves. 

For  an  animal  one  month  old,  it  is  assumed  that  the  energy  con- 
tent of  the  increase  in  live  weight  was  the  same  as  the  average  of 
Soxhlet's  respiration  experiments,  viz.,  1170  Cals.  per  pound,  and 
that  this  increased  at  a  uniform  rate  to  a  maximum  of  3000  Cals.  per 
pound  at  1 8  months  old.  The  observed  daily  gain  of  energy  has  been 
computed  per  1000  pounds  live  weight  to  eliminate  the  influence 
of  the  varying  size  of  the  different  breeds.  The  average  daily  gains 
per  1000  pounds  live  weight  are  computed  for  each  breed  separately, 
and  these  means  are  again  averaged,  i.e.,  each  breed  has  been 
given  equal  weight.  None  of  the  animals  were  fattened  to  any  great 
extent. 

1  Private  communications  from  Professors  P.  F.  Trowbridge  and  C.  H  Eckles. 
Data  for  the  dairy  breeds  have  been  published  in  Bui.  135  of  the  Missouri  Station. 


4OO 


NUTRITION  OF  FARM  ANIMALS 


TABLE  92.  —  AVERAGE  GAINS  BY  GROWING  CALVES  PER  1000  POUNDS 

LIVE  WEIGHT 


APPROXIMATE  AGE 

DAILY  GAIN  IN  LIVE 
WEIGHT 

ESTIMATED  ENERGY 
CONTENT  OF  i  LB. 
OF  INCREASE 

DAILY  GAIN  OF 
ENERGY 

Months 

Pounds 

Therms 

Therms 

o-i 

12.73 

1.170 

14.89 

o-i1 

19-54 

1.170 

22.86 

1-2 

10.69 

1.272 

13.60 

2-3 

7-32 

1-374 

10.06 

3-4 

7.84 

1.476 

n-57 

4-5 

5-29 

1.578 

8-35 

5-6 

4-53 

1.  680 

7.61 

6-7 

2.05 

1.782 

3.65 

7-8 

1.99 

1.884 

3-75 

8-g 

1.94 

1.986 

3.85 

9-10 

2.68 

2.088 

5-6o 

io-n 

2-57 

2.190 

5-63 

11-12 

1.58 

2.292 

3.62 

12-18 

1.64 

2.904 

4.76 

18-24 

1.25 

3.000 

3-75 

b.  Swine.  —  Similar  approximate  estimates  may  be  made  for 
the  pig  from  data  reported  by  Henry.2  At  weekly  intervals, 
up  to  70  days  old,  the  computation  is  based  on  the  live  weights 
and  gains  shown  in  Henry^s  table.  The  gains  by  the  older 
animals  are  estimated  on  the  basis  of  his  statement 3  that  the 
larger  breeds  should  weigh  250  pounds  at  one  year,  it  being 
assumed  that  the  rate  of  gain  would  decrease  at  an  approxi- 
mately uniform  rate. 

It  is  evident  that  the  results  on  the  heavier  animals  as  compiled 
by  Henry  were  obtained  by  heavy  feeding  for  fattening,  since  it  may 
be  computed  from  the  figures  for  the  weights  and  gains  that  the  ani- 
mals would  reach  a  weight  of  about  320  pounds  at  about  10  months 
old.  The  energy  content  per  pound  of  gain  is  estimated  on  the  as- 
sumption that  it  would  increase  uniformly  from  the  average  of 
about  500  Cals.  obtained  by  Wilson  and  by  Wellmann  for  young 
pigs  (458)  up  to  2485  Cals.  as  computed  in  Table  65  of  Chapter  X 
(442)  for  Soxhlet's  swine  No.  3  at  500  days  old. 


1  Average  of  Soxhlet's  experiments. 
3Loc.  cit.,  p.  553. 


2  Feeds  and  Feeding,  xoth  Ed.,  p.  499. 


GROWTH 


401 


TABLE  93.  •*-  AVERAGE  GAINS  BY  GROWING  PIGS  PER  1000  POUNDS  LIVE 

WEIGHT 


APPROXIMATE  AGE 

DAILY  GAIN  IN  LIVE 
WEIGHT 

ESTIMATED  ENERGY 
CONTENT  OF  i  LB. 
OF  INCREASE 

DAILY  GAIN  or 
ENERGY 

Days 

Pounds 

Therms 

Therms 

0-7 

78.55 

532 

41.79 

7-14 

65-09 

559 

36.38 

14-21 

47.62 

585 

27.86 

21-28 

34.62 

612 

21.19 

28-35 

31-53 

639 

20.15 

35-42 

25.09 

665 

16.69 

42-49 

27.72 

693 

19.21 

49-56 

29.48 

720 

21.23 

56-63 

24.92 

750 

18.69 

63-70 

21.54 

776 

16.71 

70-90 

14.92 

827 

12.34 

90-120 

"45 

945 

10.82 

120-150 

8-43 

1063 

8.96 

150-180 

6.79 

1181 

8.02 

180-210 

5-68 

1300 

7.38 

210-240 

4.87 

1418 

6.91 

240-270 

4.26 

1536 

6.54 

270-300 

3.78 

1654 

6.25 

300-330 

3-40 

1772 

6.03 

330-360 

3.08 

1891 

5.82 

482.  Estimated  averages.  —  The  foregoing  results  have 
been  plotted  in  Fig.  39  (479)  for  comparison  with  those 
derived  from  the  computations  of  §  i,  regarding  the  rate,  of 
storage  of  energy.  By  drawing  smooth  curves  through  the 
results  for  calves  and  for  pigs,  respectively,  the  following 
approximate  estimates  of  the  average  rate  of  gain  of  energy 
by  these  two  species  have  been  obtained.  No  similar  data 
appear  to  be  available  for  other  species  of  farm  animals. 
The  graph  would  seem  to  indicate  that  the  results  for  cattle 
may  apply  fairly  well  also  to  sheep,  although  no  figures  for  the 
latter  species  are  recorded  below  300  days  old.  Preliminary 
computations  on  the  basis  of  the  live  weights  assumed  by 
Kellner  for  lambs  at  different  ages  seem  to  indicate  higher 
figures  for  the  first  six  months,  especially  for  animals  of  the 
mutton  breeds. 

2  D 


402 


NUTRITION  OF   FARM   ANIMALS 


TABLE  94.  —  ESTIMATED  RATE  OF  GAIN  OF  ENERGY  PER  DAY  AND  1000 
POUNDS  LIVE  WEIGHT 


AGE 

CATTIE 
(AND 

SHEEP?) 

SWINE 

•20  davs 

Therms 
18  o 

Therms 
20  o 

60  days                                   .               . 

13  ^ 

14.  t: 

90  days      ....          
1  20  days 

II.  O 

o  o 

II  .O 

Q  O 

i  ^o  davs 

7  ^ 

8.8 

1  80  days      

6.0 

7.c 

210  days 

52  C 

7  O 

270  davs 

CQ 

6.5 

36=;  davs 

4.7C 

6.0 

1  8  months 

4e 

24  months      .     .     .     .     ,     .     .     „     .          . 

4.  2Z 



30  months      

4.0 



It  cannot  be  claimed  that  the  foregoing  computations  are 
particularly  satisfactory.  The  data  are  scanty,  and  the  ele- 
ment of  personal  judgment  unavoidably  enters,  especially  into 
the  estimates  of  the  energy  value  of  a  unit  of  increase  in  live 
weight.  Nevertheless,  while  there  are  very  considerable 
divergencies  at  certain  points,  there  is  after  all  a  certain  general 
agreement  in  the  results,  and  they  may  perhaps  serve  as  a  first 
approximation  towards  an  expression  of  the  growth  capacity 
of  farm  animals  in  terms  of  energy  storage.  It  is  much  to  be 
regretted  that  such  a  fundamental  factor  in  determining  the 
feed  requirements  for  growing  animals  is  so  imperfectly  known 
and  the  determination  of  the  amount  and  composition  of  the 
increase  in  growth  at  different  ages,  whether  by  means  of  com- 
parative slaughter  tests  or  with  the  aid  of  respiration  or  calori- 
metric  experiments,  offers  an  interesting  field  for  investigation. 
With  the  smaller  animals,  such  as  pigs,  lambs  and  particularly 
fowls,  it  would  appear  that  such  determinations  might  be  made 
without  great  difficulty. 

483.  Total  energy  requirements.  —  The  foregoing  figures 
attempt  to  show  approximately  the  actual  storage  of  energy 
per  1000  pounds  of  live  weight  by  growing  animals  at  various 
ages.  An  adequate  ration  for  such  an  animal,  however,  must 


GROWTH  403 

not  only  supply  net  energy  equal  to  that  contained  in  the  growth 
made,  as  indicated  by  the  foregoing  table,  but  in  addition 
sufficient  net  energy  for  maintenance,  the  sum  of  the  two  being 
the  total  net  energy  required  by  the  animal.  Computing 
from  Table  94  and  from  the  estimated  live  weight  at  different 
ages  *  the  energy  storage  per  head  and  adding  the  maintenance 
requirement  computed  in  proportion  to  the  two-thirds  power 
of  the  live  weight  (347)  gives  the  total  energy  requirements 
shown  by  Table  IV  b  of  the  Appendix. 

Protein  requirements 

484.  Minimum  requirement.  —  As  with  the   energy  of   the 
feed,  the  protein  supply  of  the  growing  animal  is  essentially  a 
limiting   factor.     A   deficient   supply   or   one   lacking   certain 
essential   "  building  stones  "    (465),   may  check  growth   tem- 
porarily or  permanently  through  simple  lack  of  material,  but 
it  does  not  appear  that  a  surplus  of  protein  can  materially 
stimulate  the  rate  of  growth. 

Granting  the  approximate  accuracy  of  the  estimates  of  the 
actual  gain  of  protein  in  normal  growth  made  on  previous 
pages  (463,  479),  the  quantity  of  digestible  feed  protein  re- 
quired in  the  ration  of  the  growing  animal  at  any  particular 
age  will  depend  upon  what  proportion  of  the  latter  can  be  con- 
verted into  body  protein  and  stored  up,  i.e.,  upon  the  percentage 
utilization  of  the  feed  protein  (470).  As  was  shown  in  the 
preceding  section,  however,  this  is  very  imperfectly  known. 
If,  on  the  basis  of  Fingerling's  and  Just's  results  (471),  it  be 
assumed  that  the  utilization  may  approach  100  per  cent,  then 
the  amounts  estimated  in  Table  91  (479),  with  the  addition  of 
about  0.5  per  1000  for  maintenance,  would  be  the  least  amounts 
of  digestible  protein  which  must  be  supplied  to  support  the 
normal  increase  of  protein  tissue. 

485.  Results  in  practice.  —  As  a  matter  of  fact,  however, 
experience  seems  to  show  that  a  more  liberal  supply  of  feed 
protein  than  is  indicated  by  these  estimates  is  at  least  advan- 
tageous if  not  necessary  in  the  actual  rearing  of  animals.    While 
there  are  few  investigations  on  record  directed  specifically  to 
the  determination  of  the  minimum  protein  requirements  of 

1  In  direct  proportion  to  the  live  weight. 


404 


NUTRITION  OF  FARM  ANIMALS 


growing  animals,  there  are  a  considerable  number  of  experi- 
ments, especially  upon  immature  fattening  animals,  in  which 
the  increase  of  live  weight  has  been  determined  upon  rations 
otherwise  reasonably  similar  but  containing  varying  propor- 
tions of  protein. 

In  the  immature  fattening  animal,  it  seems  safe  to  assume  that  the 
feed  protein  (in  excess  of  maintenance)  is  applied  substantially  to  the 
support  of  growth  and  that  this  growth  goes  on  parallel  with  the 
fattening  process  but  more  or  less  independent  of  it.  There  appears 
to  be  no  evidence  that  protein  specifically  stimulates  or  aids  fatten- 
ing, so  that  conclusions  regarding  the  protein  supply  drawn  from 
fattening  experiments  may  be  regarded  as  applicable  to  growth  without 
fattening. 

If  in  such  an  experiment,  in  which  the  total  amounts  of  feed 
consumed  do  not  differ  widely,  it  appears  that  the  smaller 
amount  of  protein  has  been  as  efficient  as  the  larger  as  regards 
gain  in  live  weight,  and  if  the  gain  appears  to  be  normal  in 
amount,  there  is  a  strong  presumption  that  the  lesser  amount 
of  protein  was  at  least  sufficient  for  the  needs  of  the  animal  for 
growth  and  maintenance,  while  if  a  block  test  shows  a  normal 
character  of  increase  this  presumption  is  further  strengthened. 
Obviously,  results  of  this  sort  cannot  be  relied  on  to  fix  definitely 
the  lower  limit  of  protein  supply,  but  they  may  furnish  indica- 
tions regarding  it. 

486.  Experiments  with  cattle.  —  In  the  experiments  upon 
calves  by  Soxhlet,  De  Vries  Jzn  and  Neumann,  included  in 
Table  80  (463),  showing  the  rate  of  gain  of  protein,  the  amounts 
of  digestible  protein  consumed  as  compared  with  the  actual 
gains  were  as  follows :  — 

TABLE  95.  —  PROTEIN  CONSUMED  BY  CALVES 


PER  1000  LIVE  WEIGHT 

FEED 

AGE 

Digestible 

Gain  of 

Protein 

Protein 

Soxhlet      

Whole  milk 

iQ 

4.90 

3.22 

De  Vries  Jzn  .... 

Skim  milk 

40 

4.67 

2.19 

Neumann  

Skim  milk 

55 

5-72 

2.22 

De  Vries  Jzn.     .     .     . 

Skim  milk 

65 

3-99 

1.36 

De  Vries  Jzn  .     .     .     . 

Skim  milk 

IOO 

3-32 

I.I9 

GROWTH 


405 


In  the  light  of  Fingerling's  results  upon  suckling  calves 
(466),  however,  there  can  be  little  doubt  that  the  protein  supply 
in  these  experiments  was  unnecessarily  great,  especially  with 
the  older  animals. 

The  writer  1  has  elsewhere  discussed  some  of  the  earlier  live 
weight  results  bearing  upon  the  protein  supply  of  immature 
fattening  cattle  which  seem  to  indicate  much  higher  require- 
ments than  might  be  deduced  from  the  actual  gains  of  protein 
at  the  several  ages.  Those  results  are  here  tabulated  in  a 
slightly  altered  form  and  with  the  addition  of  a  subsequent 
experiment  by  Schneidewind.2  The  summary  of  course  repre- 
sents to  a  degree  the  judgment  of  the  writer  and  the  figures  are 
to  be  interpreted  as  indications  rather  than  as  determinations. 

TABLE  96.  —  ESTIMATED  PROTEIN  REQUIREMENTS  OF  CATTLE 


AGE 
Years 

EXPERIMENTER 

DIGESTIBLE  PROTEIN  PER 
1000  LIVE  WEIGHT 

I 

Waters 

2.OO 

ii 

Jordan 

1.63 

if 

Schneidewind 

2.00 

2 

Schneidewind 

1.60 

2 

Jordan 

1.50 

2 

Frear 

1.50 

2 

Waters 

I.5O  tO  2.OO 

2~2f 

Schneidewind 

1.67 

2* 

Mumford 

1.50  tO  2.00 

3 

Frear 

I.OO 

3 

Jordan 

1.26 

The  foregoing  estimates  correspond  in  general  with  the  pro- 
tein requirements  for  growing  cattle  as  formulated  in  the  Wolff- 
Lehmann  and  Kellner  feeding  standards  (790-793) .  In  experi- 
ments upon  two  steers,  directed  principally  to  other  questions, 
Armsby  and  Fries 3  observed  a  normal  rate  of  increase  in  weight 
upon  rations  containing  amounts  of  digestible  protein  much 
smaller  than  are  called  for  by  current  feeding  standards,  although 
still  in  excess  of  the  estimated  normal  gain  of  protein  for  the  cor- 

1  U.  S.  Dept.  of  Agr.,  Bur.  Anim.  Indus.,  Bui.  108  (1908),  pp.  60-65. 
2Landw.  Jahrb.,  36  (1907),  687. 
.  3U.  S.  Dept.  of  Agr.,  Bur.  Anim.  Indus.,  Bui.  128  (1911),  pp.  88-90. 


406 


NUTRITION  OF   FARM   ANIMALS 


responding  ages.     The  experiments  do  not  show,  however,  that 
these  amounts  might  not  have  been  still  further  reduced. 

TABLE  97.  —  DIGESTIBLE  PROTEIN  PER  1000   POUNDS  LIVE  WEIGHT.  — 
ARMSBY  AND  FRIES 


STEER  A 

STEER  B 

Approximate  Age 

Digestible  Protein 

Approximate  Age 

Digestible  Protein 

Months 

Pounds 

Months 

Pounds 

95 

.      1.42 

12 

1.64 

18 

1.40 
1.09 

!J* 

1.77 
1.25 

2sf 

1.03 
0.72 

22 
27 

1.23 
0.85 

Henry  and  Morrison  1  likewise  report  the  results  of  unpub- 
lished experiments  by  Haecker  in  which  growing  fattening 
steers  made  satisfactory  gains  on  amounts  of  digestible  protein 
intermediate  between  those  recommended  by  Kellner  for  beef 
and  for  dairy  breeds. 

On  the  other  hand,  Fingerling's  investigations  on  calves 
4-j-i 1  months  old,  already  cited  in  a  discussion  of  the  utiliza- 
tion of  feed  protein  (471),  indicate  that  a  much  lower  level  of 
protein  supply  may  be  adequate  to  support  normal  growth. 

The  experiments 2  were  made  upon  four  grade  or  full-blood  Sim- 
menthaler  calves  from  four  to  seven  months  old  at  the  beginning  of 
the  trials,  and  belonging  to  early-maturing  strains.  The  rations  fed 
consisted  of  a  basis  of  hay  or  straw,  or  both,  to  which  were  added  in 
varying  proportions  wheat  gluten,  peanut  oil  and  starch  with  the 
necessary  amount  of  salt.  The  protein  supply  was  varied  by  varying 
the  amount  of  wheat  gluten,  the  energy  values  of  the  rations  being 
kept  as  nearly  identical  as  possible  by  corresponding  changes  in  the 
starch  and  oil.  The  experiments  were  intended  to  test  the  necessity 
for  the  relatively  large  amounts  of  protein  called  for  by  the  current 
standards  and  also  the  influence  of  a  deficient  energy  supply  upon  the 
gain  of  protein. 

As  appears  from  Table  87,  the  medium  rations,  supplying  in 
the  neighborhood  of  1.2  pounds  of  protein  per  1000  pounds 
live  weight,  were  clearly  sufficient  to  meet  the  demands  of 
the  maximum  possible  protein  gain,  since  an  increase  of  the 

1  Feeds  and  Feeding,  isth  Ed.,  p.  670.  2  Landw.  Vers.  Stat.,  76  (1912),  i. 


GROWTH 


407 


digestible  protein  to  more  than  double  that  amount  failed  to 
produce  any  greater  gain  but  simply  increased  the  protein 
katabolism.  That  such  was  the  case  is  likewise  indicated  by 
the  fact  that  the  actual  gains  of  protein  per  1000  live  weight 
in  these  cases  agree  very  well  with  those  computed  by  the  use  of 
the  formula  on  page  378,  tending  to  be  greater  rather  than  less.1 
487.  Experiments  with  sheep.  —  The  amounts  of  digestible 
protein  necessary  for  growing  sheep  as  formulated  by  Wolff  in 
his  original  feeding  standards  were  based  upon  experiments  of 
his  own 2  in  which  the  digestibility  of  the  feed  and  the  gain  in 
live  weight  were  determined.  Later  Weiske3  made  a  series 
of  ten  determinations  of  the  nitrogen  balance  of  two  lambs  at 
ages  ranging  from  four  to  twenty-four  months.  The  rations 
consumed  were  meadow  hay  with  a  decreasing  proportion  of 
grain  (peas)  in  Periods  I  to  VII  and  of  hay  alone  in  the  re- 
maining periods,  and  the  rate  of  increase  in  live  weight  was 
somewhat  greater  than  that  of  similar  animals  on  pasture.  The 
following  table  contains  the  results  of  both  investigations. 

TABLE  98.  —  PROTEIN  CONSUMED  BY  GROWING  SHEEP 


AGE 

DIGESTIBLE  PROTEIN 
PER  1000  POUNDS 
LIVE  WEIGHT 

EXPERIMENTER 

4  to    5  months                  .     . 

Pounds 
1  76 

Weiske 

5  to    6  months  

3.26 

Weiske 

5  to    6  months 

a  16 

Wolff 

6  to    7  months                      .     . 

2.78 

Weiske 

6  to    8  months  
7  to    9  months  
8  to    9  months  ...          . 

2.96 
2.76 
1.87  4 

Wolff 
Weiske 
Wolff 

9  to  10  months  
10  to  ii  months  
9  to  12  months  
1  1  to  1  2  months 

2.38 
2.30 
1.38  4 

2  l6 

Weiske 
Weiske 
Wolff 
Weiske 

12  to  14  months  

1.96 

Weiske 

12  to  14  months 

i  61 

Wolff 

14  to  15  months  

I.Q2 

Weiske 

24  months 

I  22 

Weiske 

1  The  one  exception  to  the  above  statement  is  the  case  animal  G  in  Period  III, 
in  which  the  energy  content  of  the  ration  was  somewhat  low. 

2Landw.  Jahrb.,  2  (1873),  221.  3  Ibid.,  9  (1880),  205. 

4  Believed  by  Wolff  to  be  too  low. 


408 


NUTRITION  OF  FARM   ANIMALS 


Bull  and  Emmett 1  have  compiled  the  results  of  fifty  American 
experiments  on  fattening  lambs,  comprising  5127  animals, 
and  computed  the  protein  and  net  energy  content  of  the  rations 
consumed.  They  divide  the  animals  into  four  classes  accord- 
ing to  the  live  weight,  and  subdivide  these  classes  into  groups 
according  to  the  amount  of  digestible  protein  consumed.  A 
comparison  of  these  groups  shows  in  general  that  in  each  class, 
even  with  a  liberal  supply  of  feed  energy,  the  rate  of  growth 
increased  as  the  supply  of  protein  increased  up  to  a  certain 
fairly  well-defined  amount,  beyond  which  a  further  increase 
of  protein  had  in  general  little  or  no  effect.  The  authors  es- 
timate the  amounts  of  digestible  protein  necessary  to  ensure 
satisfactory  gains  by  fattening  lambs  as  follows :  — 

TABLE  99.  —  ESTIMATED  PROTEIN  REQUIREMENTS  OF  FATTENING   LAMBS 


LIVE  WEIGHTS 

ESTIMATED  AGE 

DIGESTIBLE  PROTEIN  PER 
1000  LB.  LIVE  WEIGHT 

Pounds 

Months 

Pounds 

50-70 
70-90 

5 
7 

3-1-3-3 
2.5-2.8 

90-110 

9 

2.2-2.4 

110-150 

15 

1.4-1.9 

On  the  other  hand,  Just's  results  on  lambs  recorded  in  Table 
88  (471),  like  those  of  Fingerling  in  calves,  point  to  a  much 
lower  protein  requirement. 

488.  Experiments  with  swine.  —  As  is  illustrated  in  Table 
93  (481  b),  the  swine  is  distinguished  above  other  farm  quad- 
rupeds by  its  very  rapid  growth,  especially  in  the  earlier  stages. 
The  young  pig  is  able  to  double  his  weight  in  little  more  than 
a  week  and  to  nearly  treble  it  in  two  weeks,  a  rate  of  growth 
reached  or  exceeded  by  no  farm  animal  with  the  possible  ex- 
ception of  young  fowls. 

Such  a  rapid  rate  of  growth  implies,  of  course,  a  correspond- 
ingly large  storage  of  protein,  a  conclusion  fully  confirmed  by 
the  investigations  of  Ostertag  and  Zuntz,  of  Wilson,  and  of 
Sanford  and  Lusk,  cited  in  §  i  (463)  which  showed  an  average 

1  Ills.  Expt.  Sta.,  Bui.  166  (1914). 


GROWTH  409 

daily  gain  of  from  six  to  nine  pounds  of  protein  per  thousand 
live  weight  during  the  first  sixteen  days  after  birth.  Plainly, 
young  pigs  need  a  relatively  large  supply  of  protein  in  their  feed, 
but  unfortunately  no  attempts  have  thus  far  been  reported  to 
determine  the  minimum  of  feed  protein  necessary  at  different 
ages  and  especially  by  older  pigs,  simply  to  ensure  normal 
growth.  There  are  on  record,  however,  a  considerable  number 
of  experiments  in  which  rations  supplying  varying  amounts  of 
protein  have  been  fed  to  fattening  pigs  and  the  effects  upon  the 
make-up  of  the  carcass  and  upon  the  rate  of  increase  in  live  weight 
observed.  These  experiments  have  served  to  demonstrate  in  a 
striking  manner  the  practical  advantages  of  a  liberal  protein 
supply  and  while  in  many  instances  the  minimum  protein  re- 
quirement may  have  been  considerably  exceeded,  nevertheless, 
the  results  as  a  whole  are  perhaps  no  less  useful  as  a  guide  in 
practice. 

It  is  impossible  to  include  here  even  an  enumeration  of  the  large 
number  of  experiments  of  this  sort.  For  a  summary  of  earlier  inves- 
tigations the  student  may  be  referred  to  the  summary  published  by 
Wolff  in  1876. 1  A  considerable  number  of  earlier  experiments  in  the 
United  States  as  compiled  by  the  writer  gave  results  of  the  same 
general  nature. 

The  later  experiments  upon  this  subject  may  be  divided  into  those 
directed  more  specifically  to  the  determination  of  the  influence  upon 
quality  and  chemical  composition  of  the  carcass  and  those  in  which 
the  increase  in  live  weight  was  the  principal  criterion. 

489.   Effect  of  insufficient  protein  upon  the  carcass  of  pigs.  — 

Striking  results  as  to  the  make-up  of  the  carcass  in  young  pigs 
have  been  reported  by  several  investigators  in  experiments  in 
which  exclusive  maize  feeding  was  compared  with  the  use  of 
mixed  rations  supplying  much  more  protein  and  ash.  The 
trials  have  been  popularly  spoken  of  as  "  Feeding  for  fat  and 
for  lean."  In  reality  they  are  a  study  of  the  effect  of  inade- 
quate protein  (and  ash?)  supply  in  limiting  growth.  The 
subject  was  first  taken  up  by  Sanborn 2  and  soon  after  by 
Henry.3  In  general  it  was  found  that  in  the  pigs  receiving  the 

1  Ernahrung  der  landwirtschaftlichen  Nutztiere,  pp.  465-496. 

2  Mo.  Agr'l  College,  Bui.  10,  14  and  19. 

3  Wis.  Expt.  Sta.,  Rpts  4,  5,  6,  17,  18,  19  and  21. 


410  NUTRITION   OF   FARM   ANIMALS 

low  protein  (maize)  rations  the  weights  of  blood,  of  internal 
organs  and  in  some  cases  of  certain  individual  muscles  were 
relatively  less  than  with  comparable  animals  receiving  the 
high  protein  (mixed)  rations,  while  on  the  other  hand,  the 
deposits  of  adipose  tissue  appeared  notably  greater  in  the  maize- 
fed  animals. 

Since  these  investigations  were  made  it  has  become  a  well-recog- 
nized fact  that  the  mixed  proteins  of  maize  are  inadequate  to  sup- 
port rapid  growth  (783)  and  the  results  reached  are  to  be  regarded 
as  being  to  a  considerable  degree  the  expression  of  this  qualitative 
deficiency. 

As  regards  the  quantitative  aspect  of  the  experiments  it  is  to  be 
remarked  that  in  most  instances  the  difference  between  the  rations 
as  regards  protein  was  purposely  made  large.  While  the  experiments 
have  made  it  clear  that  exclusive  maize  feeding  fails  to  afford  an  ade- 
quate supply  of  protein  for  growing  pigs,  it  does,  not  follow  that  as 
large  quantities  of  protein  as  were  contained  in  the  contrasting  rations 
were  necessary.  In  the  later  Wisconsin  experiments  especially,  as 
the  writer  has  pointed  out,1  the  gain  in  live  weight  was  often  little 
greater  on  the  high  protein  than  on  the  low  protein  rations  and  some- 
times even  less. 

Furthermore,  while  the  animals  were  compared  more  or  less  ex- 
tensively as  to  the  weights  of  the  various  organs  at  the  close  of  the 
feeding,  and  in  one  instance  at  least  the  carcasses  were  analyzed,  the 
experiments  were  not  of  the  nature  of  comparative  slaughter  tests 
and  did  not  afford  data  for  computing  the  actual  amount  of  protein 
gained.  Moreover,  the  results  upon  the  carcasses  analyzed  2  seem  to 
indicate  that  the  rations  affected  the  adipose  tissue  as  to  its  distribu- 
tion through  the  carcass  rather  than  as  to  its  total  amount. 

Finally,  the  striking  results  as  to  general  thrift,  and  especially  as 
to  the  growth  and  strength  of  the  bones,  are  probably  to  be  attributed 
to  differences  in  the  ash  supply  (496) ,  quite  as  much  as  to  differences 
in  the  protein  supply. 

On  the  whole,  while  these  investigations  are  valuable  from 
the  standpoint  of  practice  as  a  demonstration  of  the  ill  effects 
of  a  deficient  amount  or  quality  of  protein,  it  cannot  be  said 
that  this  class  of  experiments  affords  very  definite  information 
as  to  the  actual  protein  requirements  of  pigs. 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  108  (igo8),  p.  74. 

2  Iowa  Expt.  Sta.,  Bui.  48  (1900),  pp.  373-451;    U.  S.  Dept.  Agr.,  Bur.  Anim. 
Indus.,  Bui.  108,  p.  75. 


GROWTH  411 

490.  Fattening  experiments  with  pigs.  —  Of  the  more  recent 
experiments  upon  the  influence  of  the  protein  supply  upon  the 
rate  of  gain  of  immature  fattening  pigs,  four  series  made  by  the 
Halle  Experiment  Station  at  Lauchstadt 1  and  a  series  of  co- 
operative experiments  at  a  number  of  the  German  experiment 
stations  under  Kellner's  general  direction  are  of  special  interest. 
While  these  relate  primarily  to  fattening,  the  comparative 
results  with  rations  of  equal  energy  content  should  furnish 
some  indications  as  to  the  sufficiency  of  the  protein  supply, 
since  the  rate  of  increase  of  protein  tissue  can  hardly  be  sup- 
posed to  differ  materially  from  that  in  simple  growth  without 
fattening. 

In  the  Halle  experiments  it  is  interesting  to  note  the  gradual 
lowering  of  the  average  protein  supply  from  the  high  level  of 
the  first  series.  The  final  series  seems  to  show  that  satis- 
factory results  may  be  obtained  from  rations  whose  protein 
content  per  1000  pounds  at  the  different  weights  of  the  animal 
is  as  follows,  although  the  earlier  trials  seem  to  indicate  some- 
what higher  figures. 

TABLE  100.  —  ESTIMATED  PROTEIN  REQUIREMENTS  OF  FATTENING  PIGS 

At  weight    77-100  Ib 4.0  Ib. 

At  weight  110-165  Ib 3.0  Ib. 

At  weight  165-220  Ib 2.0-2.5  Ib. 

At  weight  over  220  Ib 2.0  Ib. 

In  1906  cooperative  experiments  were  initiated  by  the  Ger- 
man Agricultural  Council  at  a  number  of  German  experiment 
stations  upon  the  value  of  potatoes  as  feed  for  fattening  pigs 
and  especially  upon  the  protein  supply  necessary  for  their 
most  complete  utilization.  The  results  of  experiments  upon 
this  point  at  eleven  stations,  upon  a  total  of  184  animals,  have 
been  discussed  by  Kellner  2  under  whose  general  direction  the 
work  was  done.  According  to  Kellner  3  young  fattening  pigs 
should  receive  per  1000  live  weight  the  following  amounts 
of  protein :  — 

1  Landw.  Jahrb.,  28  (1899),  947  ;  31  (1902),  916 ;  36  (1907),  679 ;  39,  Ergzbd.  Ill 
(1910),  179. 

2  Ber.  Deut.  Landw.  Rat,  Heft  3  (1908). 

3  Die  Ernahrung  der  landw.  Nutztiere,  $th  Ed.,  p.  488. 


412  NUTRITION  OF   FARM   ANIMALS 

TABLE  101.  —  KELLNER'S  STANDARDS  FOR  FATTENING  PIGS 


AGE 

AVERAGE  LIVE  WEIGHT 

DIGESTIBLE  PROTEIN  PER 

IOOO 

Months 

Kgs. 

2-3 

20 

6.2 

3-5 
5-6 
6-8 

50 
65 
QO 

4-5 
3-5 
3-o 

9-12 

I30 

2.4 

The  outcome  of  the  cooperative  experiments  tended  to  con- 
firm these  standards,  indicating  that  any  considerable  departure 
from  them  will  fail  to  meet  the  requirements  of  rapid  growth  in 
the  best  strains  of  animals  or  to  secure  the  largest  returns. 
On  the  other  hand,  the  fourth  Lauchstadt  series  perhaps  points 
in  the  direction  of  lower  standards,  especially  for  the  more 
mature  animals.  For  breeding  animals  Kellner  recommends 
somewhat  smaller  amounts  of  protein,  viz. :  — 

TABLE  102.  —  KELLNER'S  STANDARDS  FOR  GROWTH  OF  PIGS 


AGE 

LIVE  WEIGHT 

PROTEIN  PER 

IOOO 

Months 

Kgs. 

2-3 

20 

6.2 

3-5 

40 

4.0 

5-6 

55 

3-0 

6-9 

80 

2-3 

9-12 

120 

1.7 

Dietrich  1  recommends  notably  larger  amounts  of  protein, 
although  he  too  recommends  less  for  breeding  than  for  fattening 
animals.  His  figures  for  fattening  pigs  are  6.0  to  7.0  per  1000 
up  to  the  age  of  about  6  months,  followed  by  a  gradual  reduc- 
tion to  3.3  per  thousand  at  7  to  8  months.  For  breeding  animals 
his  figures  are  5.0  to  5.5  up  to  6  months  of  age,  gradually  dimin- 
ishing from  that  point  to  2.0  at  maturity. 

491.  General  conclusions.  —  It  is  apparent  from  the  fore- 
going paragraphs  that  the  evidence  regarding  the  protein  re- 

1  Ills.  Expt.  Sta.,  Circulars  126,  133  and  153. 


GROWTH  413 

quirements  for  growth  is  fragmentary  and  more  or  less  con- 
flicting. On  the  one  side  are  investigations  like  Fingerling's 
on  cattle  and  Just's  on  sheep  (486,  487)  which  appear  to  show 
that  it  is  possible  for  the  animal  to  support  what  seems  a  normal 
rate  of  growth  upon  a  supply  of  protein  little  greater  than  the 
maintenance  requirement  plus  the  amount  actually  stored. 
On  the  other  side  stand  the  results  of  experiments  and  observa- 
tions upon  the  fattening  of  immature  animals,  in  which  rations 
at  least  approximately  equal  as  to  their  content  of  net  energy, 
and  therefore  presumably  equally  effective  for  simple  fattening, 
have  produced  a  greater  increase  in  weight  when  they  contained 
relatively  much  more  protein  than  the  results  of  the  other  class 
of  experiments  would  indicate  to  be  necessary.  Further  con- 
sideration of  this  apparent  conflict  of  evidence,  however,  shows 
that  the  two  classes  of  experiments  are  hardly  comparable. 

For  one  thing,  the  experiments  in  which  a  relatively  high 
protein  supply  seemed  advantageous  were  all  fattening  ex- 
periments. The  effect  of  the  feed  was  measured  by  the  gain  in 
live  weight,  which  itself  is  a  somewhat  uncertain  criterion, 
while  a  considerable  share  of  this  increase  was  due  to  a  storage 
of  fat  rather  than  of  protein.  Fingerling's  and  Just's  experi- 
ments, on  the  contrary,  relate  distinctly  to  growth  and  the 
comparisons  are  based  on  the  actual  amounts  of  protein  tissue 
produced,  although  it  must  be  admitted  that  any  experimental 
errors  would  probably  tend  to  make  the  excretion  of  nitrogen 
appear  too  low,  and  therefore  the  gain  of  protein  too  high. 

Another  important  difference  between  the  two  classes  of 
experiments  lies  in  the  nature  of  the  rations.  In  the  metab- 
olism experiments  they  were  composed  largely  of  commercially 
pure  nutrients  such  as  starch,  oil,  etc.,  with  only  the  amount 
of  roughage  necessary  to  supply  bulk,  and  in  particular,  the 
variations  in  the  protein  supply  were  effected  by  changes  in 
the  amount  of  commercially  pure  wheat  gluten.  In  the  fatten- 
ing experiments,  on  the  contrary,  the  higher  protein  content  of 
the  rations  was  obtained  by  the  use  of  the  ordinary  protein- 
rich  feeding  stuffs.  What  these  experiments  really  show  is  that 
a  larger  proportion  of  these  feeding  stuffs  was  advantageous, 
but  it  does  not  necessarily  follow  that  this  advantage  was  due 
to  the  added  protein.  For  one  thing  such  a  modification  of 
the  rations  must  have  affected  the  ash  supply  to  a  certain  extent. 


414  NUTRITION  OF  FARM  ANIMALS 

In  particular,  however,  the  influence  of  those  accessory  sub- 
stances or  "  growth  substances  "  (498,499)  which  recent  investi- 
gations have  shown  to  play  such  an  important  part  in  condition- 
ing growth  is  to  be  considered.  It  seems  not  impossible  tnat 
high-protein  feeds  may  in  some  such  way  have  a  stimulating 
effect  upon  the  capacity  for  growth  quite  independently  of  their 
protein  content.  On  the  other  hand,  however,  any  such  stimu- 
lating effect  upon  growth  would  be  absent  in  experiments  made 
with  pure  nutrients  added  to  a  basal  ration  of  hay  or  straw,  and 
yet  a  fairly  normal  rate  of  increase  seems  to  have  been  maintained. 
On  the  whole,  one  can  hardly  fail  of  the  impression  that  the 
requirements  for  protein  as  such  in  growth  have  been  over- 
estimated and  that  the  organism  may  utilize  its  protein  supply 
more  economically  than  the  current  feeding  standards  would 
indicate;  in  other  words,  that  the  actual  protein  supply  may 
be  made  considerably  smaller  than  has  been  supposed  before 
it  becomes  a  limiting  factor  in  growth.  Until  this  impression 
is  confirmed  by  more  extensive  investigation,  however,  it  ap- 
pears the  safer  course  to  adhere  provisionally  to  the  accepted 
standards,  and  the  protein  requirements  for  growth  as  estimated 
in  Table  IV  b  of  the  Appendix  are  based  upon  those  formulated 
by  Kellner. 

Ash  requirements 

492.  Growth  involves  storage  of  ash.  —  The  growing  animal, 
like  the  mature  one,  requires  mineral  ingredients  for  the  pur- 
poses enumerated  in  Chapter  V  (268-272),  but  in  addition  to 
this  the  formation  of  new  tissue  and  especially  of  the  skeleton 
involves  the  storage  of  ash  ingredients  which  must  be  derived 
from  the  feed.     This  is  shown  clearly  by  the  data  recorded  in 
§  i  (458)  regarding  the  composition  of  the  increase,  its  ash 
content,  aside  from  one  exceptional  case,  ranging  from  1.42  per 
cent  to  6.18  per  cent. 

493.  Rate  of  storage  in  growth.  —  Data  regarding  the  rate 
of  storage  of  mineral  elements  in  growth  are  not  very  numerous 
and  are  largely  confined  to  experiments  on  the  two  important 
elements  calcium  and  phosphorus.     The  principal  investiga- 
tions are  those  of  Soxhlet,1  Neumann,2  Lehmann,3  and  Weiske  4 

1  ier  Ber.  Versuch-Station  Wien,  pp.  101-155.       2  Jour.  Landw.,  41  (1893),  343- 
3Landw.  Vers.  Stat.,  1  (1859),  68.  4  Jour.  Landw.,  21  (1873),  139- 


GROWTH 


415 


on  calves,  those  of  Weiske J  on  lambs,  and  those  of  Forbes  2 
and  of  Weiser 3  on  pigs. 

Arranging  the  available  results  upon  the  retention  of  cal- 
cium and  phosphorus  per  1000  live  weight  in  order  of  the  age  of 
the  animals,  irrespective  of  the  species,  gives  the  following 
showing  of  the  effect  of  age  upon  the  rate  of  gain  of  these  two 
elements.  It  appears  that  in  suckling  animals,  the  rate  of 
gain  of  the  ash  ingredients,  like  that  of  protein  and  energy 
(463,  464),  is  relatively  high,  while  there  is  a  distinct  falling 
off  in  the  rate  as  the  animal  grows  older,  although  not  to  the 
same  extent  as  in  the  case  of  the  organic  nutrients. 

TABLE  103.  —  DAILY  RETENTION  PER  1000  LIVE  WEIGHT 


INVESTIGATOR 

SPECIES 

AGE 

CALCIUM 

PHOS- 
PHORUS 

Soxhlet  

Calf 

Days 
i8| 

0.208 

0.118 

Calf 

e4| 

0.  1  1  1 

o  083 

Lehmann  .  .  . 

Calf 

140 

0.008 

0.0=53 

Weiske  
Weiske  
Forbes  

Calf 
Lamb 
Pig 

150 

177 
273 

0.073 
0.046 
0.042 

0.059 

O.O2O 
O.O^I 

Weiske  
Weiske  
Weiser  

Lamb 
Lamb 
Pig 

292 
386 

0.040 
0.038 
0.029 

0.031 

0-035 

O.O2O 

The  data  of  the  foregoing  experiments  hardly  afford  an 
adequate  basis  for  estimating  the  ash  requirements  at  different 
ages.  As  compared  with  the  amounts  of  mineral  elements  con- 
sumed in  or  assimilated  from  the  feed,  the  body,  of  even  a  very 
young  animal  contains  a  large  stock  of  these  substances  which 
can  be  drawn  upon  to  a  certain  extent  to  meet  any  temporary 
deficiency  in  the  feed.  It  is  possible,  therefore,  that  the  amounts 
retained  in  the  relatively  short  periods  of  the  foregoing  experi- 
ments may  be  less  than  are  necessary  or  desirable  for  continuous 
normal  growth.  On  the  other  hand  it  would  appear  from 
Forbes'  results  4  that,  under  favorable  conditions,  ash  may  be 
stored  in  the  bones  in  excess  of  the  actual  maintenance  needs 
and  constitute  a  reserve  of  mineral  matter  in  the  body.  The 


1  Landw.  Jahrb.,  9  (1880),  205. 
3Biochem.  Ztschr.,  44  (1912),  279. 


2  Ohio  Expt.  Sta.,  Technical  Bui.  5,  p.  378. 
4  Loc.  cit.,  p.  371. 


416 


NUTRITION  OF   FARM  ANIMALS 


fact  shown  in  Chapter  IX  (435)  that  more  or  less  storage 
of  ash  elements  may  occur  even  in  the  mature  animal  points 
in  the  same  direction.  The  organism  appears  far  less  sensitive 
to  fluctuations  of  its  daily  supply  of  ash  than  to  those  of  the 
organic  nutrients  because  it  has  relatively  a  much  larger  re- 
serve to  draw  upon. 

494.  Total  retention  during  growth.  —  Some  notion  of  the 
total  amounts  of  mineral  elements  assimilated  during  growth 
may  be  secured  by  computing  from  Lawes  and  Gilbert's  anal- 
yses of  the  ash  of  the  entire  bodies  of  farm  animals  the 
weights  of  each  ash  ingredient  contained  in  them.  Thus  if 
the  live  weight  at  one  year  old  be  assumed  to  be  for  cattle  400 
kilograms  (880  pounds)  and  for  sheep  50  kilograms  (no  pounds) 
and  for  a  six:  months'  old  pig  50  kilograms,  then,  applying  the 
analyses  of  the  half-fat  ox,  store  sheep  and  store  pig  respectively, 
the  total  amounts  of  mineral  elements  in  the  bodies  and  the 
average  daily  retention  per  head  (including  the  stock  con- 
tained in  the  bodies  at  birth  in  the  case  of  the  sheep  and  pig) 
would  be  as  follows :  — 


TABLE  104.  —  TOTAL  RETENTION  or  ASH  INGREDIENTS  DURING  GROWTH 


CALF 

YEARLING 
CATTLE 

GAIN  BY 
CATTLE 
DURING 
IST  YEAR 

YEARLING 
SHEEP 

6  MONTHS' 
OLD  PIG 

Total  in  body 

Grams 

Grams 

Grams 

Grams 

Grams 

Potassium   

62 

679 

617 

72 

82 

Sodium 

A.O 

A-1A 

2Q4. 

A  A 

A\ 

Calcium       ..... 

t\\j 
423 

tot 

6032 

OV^f 

5609 

*r*r 

472 

ij.X 

386 

Magnesium      .... 

17 

203 

186 

17 

16 

Phosphorus      .... 

241 

3213 

2972 

259 

233 

Chlorin  . 

2  2 

277 

214 

^6 

20 

Average  retention  per  day 

o 

O  1 

O^ 

y 

and  head 

Potassium   

— 

— 

1.64 

O.2O 

0-45 

Sodium  

— 

— 

1.  08 

0.12 

0.22 

Calcium       

— 

— 

15-37 

1.29 

2.  II 

Magnesium      .... 

— 

— 

0.50 

O.O5 

O.O9 

Phosphorus      .... 

— 

— 

8.14 

0.71 

1.27 

Chlorin  

— 

— 

0.59 

O.IO 

0.16 

GROWTH 


417 


In  order  to  compare  the  figures  thus  obtained  with  the  results 
recorded  in  the  previous  paragraph  for  the  retention  during 
short  periods,  it  is  necessary  to  eliminate  the  influence  of  vary- 
ing weight  by  computing  the  results  per  1000.  The  retention 
of  calcium  and  phosphorus  as  thus  computed  agrees  very  well 
with  that  found  in  the  balance  experiments  with  the  exception 
of  Forbes'  high  result  for  phosphorus  with  the  pig.  On  the 
other  hand  the  computed  retention  of  the  alkalies  is  strikingly 
less,  a  fact  for  which  no  obvious  reason  appears. 

TABLE  105.  —  AVERAGE  DAILY  RETENTION  PER  1000  LIVE  WEIGHT 


CATTLE 
DURING 
FIRST 
YEAR 

SHEEP 
DURING 
FIRST 
YEAR 

PIG  DUR- 
ING FIRST 
6  MONTHS 

Potassium 

o  008 

o  008 

o  018 

Sodium                                      

O.OCK 

O.OO2 

o  ooo 

Calcium  .          

O.Oyi 

0.0^2 

0.084. 

A!  a,2  ne  slum 

O  OO2 

o  002 

o  004. 

Phosphorus                      .          

O.O37 

0.028 

O.O^I 

Chlorin    .                    

O.OO^ 

0.004 

0.006 

On  the  whole  it  appears  that  our  knowledge  of  the  ash  require- 
ments of  growing  animals,  that  is,  of  the  actual  amounts  stored 
up  in  normal  growth,  is  quite  fragmentary  and  unsatisfactory. 

495.  Availability  of  ash  ingredients  of  feed.  —  If  it  is  dif- 
ficult to  formulate  from  existing  data  any  trustworthy  estimates 
of  the  ash  requirements  of  growing  animals,  it  is  even  more 
difficult  to  make  any  definite  statements  regarding  the  total 
amount  of  any  particular  element  which  must  be  supplied  in 
the  feed  in  order  to  meet  those  requirements,  although  to  the 
extent  to  which  the  results  recorded  in  the  previous  paragraphs 
are  trustworthy,  it  is  possible  to  formulate  the  minimum  supply. 
Thus,  Weiske's  results  on  sheep  show  a  retention  of  from  20 
to  35  mgrs.  of  phosphorus  per  kilogram  of  live  weight.  If 
these  figures  represent  the  normal  requirements,  it  is  evident 
that  a  ration  containing  less  than  this  amount  would  not  supply 
enough  phosphorus  for  normal  growth.  What  surplus  above 
this  amount  is  necessary  in  the  feed  would  depend  on  the  pro- 
portion of  the  feed  phosphorus  which  is  capable  of  solution  in 


2  E 


4i8 


NUTRITION  OF  FARM  ANIMALS 


the  digestive  tract,  and  still  more  upon  the  effect  of  other  ele- 
ments on  the  elimination  of  phosphorus.  An  amount  of  this 
element  amply  sufficient  to  meet  the  normal  demand  when 
supplied  in  one  ration  might  be  quite  inadequate  in  another  of 
a  different  character. 

Since  the  intestines  are  the  normal  path  of  excretion  for 
some  ash  elements  (164,  199),  a  computation  of  the  digesti- 
bility of  these  elements  in  the  ordinary  sense,  by  comparing 
the  amounts  in  feeds  and  feces,  gives  an  entirely  false  idea  of 
their  availability.  Moreover,  it  was  shown  in  Chapter  IX 
(429-433)  that  the  rate  at  which  mineral  elements  are  lost 
from  the  body  depends  to  a  large  degree  upon  the  qualitative 
composition  of  the  ash  of  the  feed,  variations  in  the  supply  of 
one  element  sometimes  affecting  materially  the  gain  or  loss  of 
another.  In  particular  it  was  pointed  out  that  the  proportion 
of  acid  and  basic  elements  and  to  a  less  degree  the  ratio  of 
potassium  to  sodium  may  have  striking  effects  of  this  sort. 
For  example,  in  Weiser's  experiments  on  pigs  (493),  the  ad- 
dition of  5  grams  of  calcium  carbonate  to  a  ration  of  1000 
grams  of  maize  not  only  changed  a  loss  of  calcium  into  a  gain 
but  also  produced  the  same  effect  on  the  phosphorus  balance, 
so  that  a  phosphorus  supply  which  was  previously  insufficient 
to  maintain  the  body  was  able  to  support  a  material  gain. 


TABLE  106.  —  ASH  BALANCE  OF  SWINE  WITH  AND  WITHOUT  CALCIUM 
CARBONATE 


CALCIUM 

PHOSPHORUS 

Maize  alone 
In  feed 

o  1006 

2  6731 

In  feces 

1.1298 

2.2^70 

In  urine     

0.1384 

0.8134 

Balance 

i  0686 

O  3Q73 

Maize  and  CaCO2 
In  feed      
In  feces 

1.2682     1.2682 

2.1950 
1.2602 

3.0704    3.0704 

2.8167 
1.6960 

In  urine     
Balance 

0.0766 
o  8582 

0.2714 

o  8403 

2.1950    2.1950 

2.8167    2.8167 

GROWTH  419 

It  has  been  maintained,  principally  on  the  basis  of  Soxhlet's 
experiments  on  calves  (493),  that  the  availability  of  the  ash 
ingredients  of  milk,  and  particularly  of  its  calcium  and  phos- 
phorus, is  especially  high.  The  percentages  retained  in  the 
body  on  the  average  of  the  five  trials  were :  — 

Total  ash 53.0 

Potassium 20.7 

Sodium        29.1 

Calcium 97.0 

Magnesium 30.5 

Phosphorus 72.5 

Chlorin        3.8 

Neumann's  experiments  with  somewhat  older  calves  (493), 
however,  render  it  evident  that  the  cause  of  the  high  retention 
of  calcium  and  phosphorus  was  the  large  demand  for  these 
elements  in  the  body.  It  can  hardly  be  supposed  that  these 
elements  are  less  assimilable  in  the  skim  milk  used  in  Neumann's 
experiments,  yet  the  percentage  retention  was  scarcely  more 
than  one-half  as  great  as  in  Soxhlet's  experiments,  viz.,  in  the 
experiments  on  skim  milk  alone. 


PERIOD  i 

PERIOD  3 

PERIOD  5 

Calcium  

47  8% 

44.  ^  % 

A  A    I  % 

Phosphorus  

ci.i  % 

42.7  % 

41  8% 

The  older  animals  obviously  required  less  of  these  elements 
and  therefore  excreted  the  excess,  the  phosphorus  in  the  urine 
and  the  calcium  in  the  feces. 

Lehmann's  and  Weiske's  experiments  (493)  with  older  calves 
on  mixed  rations  showed  a  percentage  availability  of  the  phos- 
phorus and  calcium  fully  as  great  as  that  observed  for  skim 
milk  in  Neumann's  experiments,  and  here  too  the  natural  con- 
clusion is  that  the  demand  for  these  elements  in  the  body, 
rather  than  any  lower  availability  per  se,  is  the  cause  of  the  less 
assimilation.  It  is  well  established  that  the  inorganic  phos- 
phates may  be  quite  completely  assimilated,  and  Fingerling  1 

1  Landw.  Vers.  Stat,  79-80  (1913),  847  J  86  (1915),  75- 


420  NUTRITION  OF  FARM  ANIMALS 

has  shown  the  same  thing  to  be  true  of  a  variety  of  organic 
phosphorus  compounds,  as  well  as  of  the  phosphorus  of  con- 
centrated feeding  stuffs,  while  in  case  of  roughages  l  an  avail- 
ability of  approximately  50  per  cent  was  observed.  These 
facts  throw  some  doubt  on  Kellner's  conclusion  that  the  feed 
should  contain  two  or  three  times  the  quantities  of  mineral 
elements  which  would  normally  be  stored  in  the  body. 

496.  Effects  of  deficiency  of  ash.  —  But  while  it  seems 
scarcely  possible  to  make  any  definite  quantitative  statements 
regarding  the  necessary  ash  supply  of  growing  animals  there  is 
abundant  evidence  of  the  evil  effects  of  an  insufficient  supply. 
In  particular,  a  deficiency  of  calcium,  as  already  indicated, 
may  have  serious  consequences  both  directly  and  on  account  of 
the  fact  that  such  a  deficiency  generally  connotes  an  acid  ash 
(431). 

Kellner  2  cites  experiments  by  Roloff  and  by  Voit,  in  which  young 
dogs  and  pigs  receiving  feed  poor  in  calcium  showed  deficient  growth 
and  developed  severe  pathological  symptoms,  the  skeleton  showing 
a  notable  deficiency  in  ash  ingredients  (Rachitis) .  Forbes  3  has  col- 
lected a  large  number  of  experiments  on  this  subject  in  some  of  which 
marked  effects  on  the  composition  of  the  bones  were  observed  while 
in  others  these  effects  were  not  very  distinct.  In  still  more  recent 
experiments  by  Weiser  4  upon  pigs,  a  diet  deficient  in  calcium  re- 
stricted the  growth  and  produced  a  skeleton  containing  an  excess  of 
water  and  organic  matter  and  deficient  in  ash.  Contrary  to  the  re- 
sults of  Aron  (428)  the  bone  ash  on  the  calcium-poor  rations  was 
deficient  in  calcium  and  contained  an  excess  of  alkalies,  especially 
sodium. 

Of  farm  animals,  pigs  are  most  likely  to  suffer  in  this  way, 
partly  because  their  growth  is  relatively  rapid  and  partly  be- 
cause they  often  receive  almost  exclusive  grain  rations  which 
are  apt  to  be  low  in  calcium  (431).  Henry  5  has  shown  that 
supplementing  such  rations  with  calcium  phosphate  or  car- 
bonate results  in  the  production  of  heavier  and  stronger  bones, 
and  Burnett 6  has  confirmed  these  results.  Hart  and  McCol- 

1  Biochem.  Ztschr.,  37  (191 1),  266. 

2  Ernahrung  der  landw.  Nutztiere,  6th  Ed.,  p.  177. 

3  Ohio  Expt.  Sta.,  Tech.  Bui.  5,  pp.  384-390- 

4  Biochem.  Ztschr.,  66  (1914),  95- 

6Wis.  Expt.  Sta.,  6th  Rpt.,  pp.  6-41 ;  Bui.  25. 
6  Neb.  Expt.  Sta.,  Buls.  94  and  107  and  23d  Rpt. 


GROWTH  421 

lum  1  found  that  confined  pigs  on  a  ration  of  maize  alone  and 
drinking  distilled  water  failed  to  grow,  while  the  addition  of  an 
artificial  mixture  of  salts  enabled  nearly  normal  growth  to  be 
made. 

With  cattle  and  sheep  a  deficiency  of  calcium  is  not  usually 
to  be  feared,  since  roughages  are  usually  rich  in  this  element. 
Straw  and  roots,  however,  are  rather  low  in  calcium  and  so  are 
certain  by-product  feeds,  especially  those  like  gluten  feed  and 
meal,  distiller's  grains,  etc.,  which  have  been  subject  to  ex- 
traction with  water. 

497.  Forms  of  phosphorus.  —  A  much  discussed  question  is 
that  of  the  relative  value  of  organic  and  inorganic  phosphorus 
compounds.  It  was  stated  in  Chapter  V  (258),  that  the  animal 
body  is  apparently  able  to  synthesize  its  organic  phosphorus 
compounds  from  inorganic  phosphorus.  Forbes 2  has  given 
a  very  complete  review  of  the  literature  of  this  subject.  His 
general  conclusion  is  that  it  has  not  been  proven  that  a  supply 
of  organic  phosphorus  is  essential,  although  he  regards  the 
proof  that  inorganic  phosphorus  can  serve  all  the  purposes  for 
which  any  animal  needs  phosphorus  as  being  incomplete.  As 
regards  the  relative  efficiency  of  the  two,  the  facts  already  noted 
in  Chapter  IX  (437,  438)  and  in  the  following  paragraphs,  re- 
garding the  importance  of  accessory  substances,  in  particular 
the  so-called  growth  substances,  in  nutrition  strongly  suggest 
that  the  apparent  superiority  of  organic  phosphorus  which  has 
been  observed  in  some  experiments  may  have  been  due  to  the 
presence  of  such  substances  accompanying  the  organic  phos- 
phorus compounds  and  not  to  the  latter  as  such. 


Accessory  substances 

498.  Relation  of  fats  to  growth.  —  It  was  mentioned  in 
Chapter  V  (265),  in  considering  the  functions  of  the  nutrients, 
that  it  had  apparently  been  shown  that  the  presence  of  a  certain 
minimum  amount  of  fat  (or  at  least  of  ether-soluble  sub- 
stances —  lipoids)  was  necessary  for  growth.  Later  investi- 
gations, however,  have  led  to  a  different  interpretation  of  these 

1  Jour.  Biol.  Chem.,  19  (1914),  373. 

2  Ohio  Expt.  Sta.,  Tech.  Bui.  5,  pp.  318  to  365. 


422  NUTRITION  OF  FARM  ANIMALS 

earlier  results.  As  the  technique  of  experimentation  with  iso- 
lated nutrients  has  been  developed  by  the  work  of  Rohmann, 
McCollum,  Osborne  and  Mendel  and  others,  it  has  become 
evident  that  it  is  not  the  lipoids  as  such  but  some  substance  or 
substances  associated  with  them  which  are  essential  to  con- 
tinued growth.  On  the  one  hand,  growth  has  been  maintained, 
for  a  considerable  time  at  least,  on  a  practically  fat-free  diet, 
while  on  the  other  hand  it  has  been  shown  that  by  no  means 
all  fats  are  capable  of  exerting  this  favorable  effect  on  growth. 

Both  McCollum  and  Osborne  and  Mendel  have  found  that  rats  fed 
mixtures  of  purified  nutrients  containing  no  fat  may  grow  normally 
for  a  considerable  time,  but  after  about  75  or  100  days,  and  after 
reaching  perhaps  f  of  the  mature  weight,  there  is  a  more  or  less  abrupt 
cessation  of  growth  followed  by  a  speedy  decline  in  weight.  Sub- 
stantially the  same  result  ensues  when  certain  forms  of  fat  (lard,  beef 
fat,  olive  oil,  almond  oil)  are  added  to  the  ration,  but  if,  on  the  other 
hand,  purified  butter-fat,  cod  liver  oil  or  certain  other  fats  be  added 
to  the  ration  of  an  animal  which  has  ceased  to  grow  and  begun  to 
decline  in  weight  this  decline  is  promptly  stopped  and  practically 
normal  growth  resumed.  These  results  indicate  the  existence  of  two 
groups  of  fats,  one  of  which  aids  growth  while  the  other  does  not. 
Evidently,  therefore,  the  growth  supporting  property  does,  not  reside 
in  the  glycerids  themselves  but  in  some  accompanying  substances. 

499.  Growth  substances.  —  On  the  basis  of  later  investiga- 
tions, McCollum  1  rejects  Funk's  hypothesis  of  the  existence 
of  numerous  specific  "  vitamins  "  and  distinguished  only  two 
growth  substances  (or  classes  of  substances),  both  of  which  are 
essential  to  growth.  One,  lipoid-soluble,  which  he  calls  fat- 
soluble  A,  is  associated  with  certain  fats,  while  the  other,  called 
water-soluble  B,  is  soluble  in  water  and  apparently  never  asso- 
ciated with  fats.  The  fat-soluble  A  is  absent  from  all  vege- 
table fats  thus  far  examined.  It  is  present  in  small  but  in- 
sufficient amounts  in  the  grains  but  appears  to  be  relatively 
abundant  in  the  leaves  of  plants. 

That  other  factors  than  these  specific  growth  substances  may 
markedly  influence  growth  is,  however,  apparent  from  recent  ex- 
periments by  Hart  and  McCollum 2  who  found  that  the  freedom 

1  Jour.  Biol.  Chem.,  23  (1915),  181  and  231 ;  25  (1916),  105 ;  Amer.  Jour.  Physiol., 
41  (1916),  333  and  361. 

2  Jour.  Biol.  Chem.,  19  (1914),  373. 


GROWTH  423 

of  a  small  paddock  in  which  they  can  root  stimulates  the  growth 
of  pigs  to  a  degree  quite  out  of  proportion  to  the  amount  of 
actual  feed  thus  obtained.  Furthermore,  they  have  shown 
that,  with  both  pigs  and  cows  (438),  rations  consisting  exclu- 
sively of  wheat  products  seem  to  have  a  direct  effect  in  hinder- 
ing growth.  The  subject  is  one  which  is  hardly  ripe  for  dis- 
cussion, but  it  opens  up  an  interesting  field  for  investigation, 
while  it  emphasizes  the  importance  of  variety  in  rations. 

No  data  have  been  published  regarding  the  percentage 
utilization  of  the  feed  actually  consumed  in  these  experiments 
as  measured  by  the  amount  of  growth  actually  made  on  the 
inadequate  rations. 


CHAPTER  XII 
MEAT   PRODUCTION1 
§  i.  NATURE  OF  MEAT  PRODUCTION 

500.  Definitions.  —  By  "  meat  "  is  understood  in  a  general 
way  the  flesh  of  an  animal  as  distinguished  from  the  skeleton 
on  the  one  hand  and  the  internal  organs,  hide  and  other  offal 
on  the  other.     Meat  in  this  general  sense  is  separable  mechani- 
cally into  adipose  tissue  ("  fat  ")  and  lean  meat,  both  of  which, 
but  especially  the  latter,  are  of  somewhat  complex  composition. 

The  adipose  tissue  (94)  consists  of  connective  tissue  in  which 
a  greater  or  less  accumulation  of  fat  has  taken  place  and  is 
essentially  a  reserve  of  non-nitrogenous,  energy-yielding  ma- 
terial. The  lean  meat,  or  meat  in  the  narrower  sense  (86), 
consists  primarily  of  muscular  tissue  along  with  more  or  less 
fat,  and  its  characteristic  ingredients  are  the  proteins. 

501.  Proportion  of  fat  and  lean  in  carcass.  —  The  proportion 
of  lean  meat  to  fat  tissue  in  the  carcass  is  naturally  quite  vari- 
able, depending  somewhat  upon  the  age  but  chiefly  on  the  feed- 
ing of  the  animal,  insufficient  nutrition  reducing  the  store  of  fat 
in  the  body  to  a  minimum  while  heavy  feeding  may  cause  the 
production  of  large  amounts  of  it.     Thus  Lawes  and  Gilbert 
found  the  proportion  of  fat  in  the  carcasses  of  the  ten  animals 
analyzed  by  them  (97)   to  vary  from  15.3  to  48.3  per  cent. 
Jordan  observed  a  range  of  18.80  to  24.62  per  cent  in  steers  2-2  J 
years  old.     Tschirwinsky  reports  the  extremes  of  10.39  an^ 
40.92  per  cent  in  pigs,  while  Wilson  found  a  minimum  of  1.31 
per  cent  in  new-born  pigs.     Atwater  2  gives  the  following  as 
the  average  composition  of  a  side  of  beef  of  medium  fatness :  — 

1  The  discussions  in  this  chapter  follow,  to  a  considerable  extent,  those  presented 
by  the  writer  in  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  108  (1908). 

2  U.  S.  Dept.  Agr.,  Office  Expt.  Stas.,  Bui.  21  (1895),  p.  35- 

424 


MEAT  PRODUCTION 


TABLE   107.  —  AVERAGE  COMPOSITION  OF.  A  SIDE  OF  BEEF  OF 
MEDIUM  FATNESS 


425 


% 

Water 

CA   77/ 

Protein                     

I7.2O 

Fat   

27.O7 

Ash                                                                                     .     . 

o  06 

IOO.OO 

Lean  cuts  of  meat,  however,  may  contain  much  less  fat  than 
is  indicated  by  the  foregoing  statement.  Thus  Grindley  and 
Emmett 1  analyzed  seven  samples  of  beef  round  from  which  the 
visible  fat  had  been  removed.  The  minimum  figure  for  fat  was 
3.19  per  cent  in  the  fresh  substance,  or  12.29  per  cent  of  the 
dry  matter.  The  average  of  the  seven  analyses  was  as  fol- 
lows :  — 

TABLE  108.  —  AVERAGE  COMPOSITION  OF  SEVEN  SAMPLES  OF  BEEF  ROUND 
WITH  VISIBLE. FAT  REMOVED 


IN  FRESH 
SUBSTANCE 

IN  WATER-FREE 
SUBSTANCE 

Water 

% 

7-3     -1Q 

% 

Ash 

113 

4.27 

Protein       

l8.70 

7O.67 

Extractives 

2  98 

1  1  O7 

Fat 

4.88 

I7.8l 

IOO.OO 

IOO.OO 

Voit  found  in  the  carefully  prepared  lean  meat  which  he 
used  as  representing  substantially  protein  feed,  and  which  had 
been  most  painstakingly  freed  from  all  visible  fat,  0.91  per  cent 
of  ether  extract  in  the  fresh  substance,  equal  to  3.77  per  cent  of 
the  dry  matter. 

The  term  meat  commonly  suggests  to  the  mind  the  muscular 
tissue  of  the  animal,  and  has  become  almost  synonymous  with 
1  Ills.  Expt.  Sta.,  Bui.  162. 


426  NUTRITION  OF  FARM   ANIMALS 

a  protein  diet.  It  is  evident,  however,  that  the  commercial 
growing  of  meat  may  involve  the  production  of  considerably 
more  fat  than  protein  and  that,  in  so  far  as  this  fat  is  actually 
consumed,  meat  is  far  from  being  the  distinctively  protein 
food  which  it  is  ordinarily  considered.  Thus  the  so-called 
"  nutritive  ratio  "  of  the  average  side  of  beef,  calculated  in  the 
usual  manner,  is  about  i :  3.5.  On  the  other  hand,  however,  it 
is  equally  true  that  the  proteins  of  meat  are  the  distinctive  in- 
gredients for  the  sake  of  which  it  is  produced  and  eaten,  while 
the  fat,  although  a  valuable  nutrient,  is  to  a  certain  extent  sub- 
sidiary and  accidental. 

502.  Processes  involved.  —  Corresponding  in  a  general 
way  to  the  two  main  constituents  of  commercial  meat,  viz., 
muscular  tissue  and  adipose  tissue,  two  distinct  physiological 
processes  are  involved  in  meat  production,  viz.,  growth  and 
fattening. 

Growth.  —  The  animal  at  birth  is  usually  regarded  as 
unfit  to  serve  as  human  food.  Moreover,  even  were  this 
not  the  case  it  would  be  in  the  highest  degree  uneconomic 
to  fail  to  utilize  the  marked  assimilative  powers  of  the 
young  animal  for  the  production  of  body  tissue  (meat) 
from  feed.  Consequently  the  production  of  meat  involves 
more  or  less  growth  in  all  cases.  This  may,  for  special  reasons, 
be  concluded  early,  as  in  the  production  of  lamb  or  veal,  but  as 
a  whole  the  world's  commercial  meat  supply  is  derived  from 
animals  at  least  approaching  maturity.  This  growth  of  animals 
from  birth  to  approximate  maturity  consists  essentially  of  an 
increase  in  the  protein  tissues  (457),  the  rate  of  which  is  es- 
sentially determined  by  the  nature  and  individuality  of  the 
animal  and  can  at  most  be  but  slightly  stimulated  by  an  in- 
creased protein  supply  (403,  484). 

Fattening.  —  Fattening,  on  the  contrary,  is  a  process  which, 
in  a  given  animal  at  least,  is  largely  under  the  control  of  the 
feeder.  Substantially  it  is  dependent  on  the  quantity  of  feed 
consumed  by  the  animal  in  excess  of  the  requirements  for 
maintenance  and  growth,  and  there  is  lacking  any  definite  proof 
that  the  actual  storage  of  energy  in  the  form  of  gain  for  a  given 
amount  of  excess  feed  is  seriously  affected  either  by  the  age  or 
the  individuality  of  the  animal.  Fattening,  therefore,  may 
take  place  at  any  age,  although  of  course  the  greater  demand 


MEAT  PRODUCTION  .        427 

for  material  for  growth  in  the  young  animal  tends  to  reduce  the 
proportion  of  the  feed  available  for  fattening. 

The  prime  object  of  fattening  (446)  is  an  improvement  in 
the  quality  of  the  meat  by  the  deposition  of  fat  between  the 
fibers  of  the  meat,  and  to  some  extent  by  increasing  the  ex- 
tractives of  the  meat  itself.  The  large  deposits  of  fat  about 
the  internal  organs  and  under  the  skin  are  incidental  to  this  and 
are  to  a  certain  extent  a  waste.  The  subcutaneous  fat  affords 
a  convenient  index  to  the  quality  of  the  meat,  and  of  course 
the  adipose  tissue  of  the  carcass  is  of  some  value,  but  these  fat 
deposits  largely  represent  the  price  paid  for  the  improved  qual- 
ity of  the  meat  proper.  It  is  not  impossible  that  the  traditions 
of  the  market  may  cause  the  process  of  fattening  to  be  pushed 
beyond  what  is  necessary. 

This  improvement  in  quality  may  be,  and  to  a  considerable 
extent  is,  secured  by  a  comparatively  short  period  of  high 
feeding  after  growth  has  been  nearly  completed.  It  is  obvious, 
however,  that  no  sharp  line  can  be  drawn  between  the  pro- 
cesses of  growth  and  fattening.  A  calf  or  yearling  may  be 
fattened  while  growing,  and  a  two-year-old  steer  will  continue 
to  grow  to  some  extent  while  being  fattened.  The  two  pro- 
cesses shade  into  each  other  and  economic  considerations  will 
decide  whether  they  shall  be  carried  on  more  or  less  simultane- 
ously by  a  single  producer  or  at  different  times  by  two  different 
individuals. 

In  brief,  meat  production  may  be  defined  as  a  combination 
of  growth  and  fattening,  which  may  be  either  simultaneous  or 
successive,  but  the  production  of  protein  tissue  is  the  primary 
object  in  view,  while  the  accumulation  of  fat,  although  adding 
to  the  nutritive  value  and  to  the  palatability  of  the  meat,  is  more 
or  less  a  secondary  matter.  The  purpose  of  the  present  chapter 
is  to  consider  the  application  of  the  principles  of  growth  and 
fattening  discussed  in  the  two  preceding  chapters  to  this  branch 
of  food  production. 

503.  Factors  of  meat  production.  —  From  the  economic 
point  of  view,  the  meat  producing  animal  may  be  looked  upon 
as  a  mechanism  by  means  of  which  the  raw  material  contained 
in  the  various  feeding  stuffs  is  converted  into  the  finished  prod- 
uct for  human  consumption.  Regarding  meat  production, 
then,  as  a  manufacturing  process,  the  amount  and  quality  of 


428  NUTRITION  OF  FARM  ANIMALS 

the  production  obtained  is  plainly  dependent  upon  three  factors : 
first,  the  efficiency  of  the  mechanism ;  second,  the  amount  and 
quality  of  the  raw  material  supplied;  third,  the  conditions 
under  which  the  mechanism  is  operated. 

§  2.  THE  ANIMAL  AS  A  FACTOR  IN  MEAT  PRODUCTION 

Of  the  three  factors  just  mentioned,  the  animal  may  fairly 
be  said  to  be  the  one  of  prime  importance.  The  success  of  the 
feeder  depends  primarily  upon  the  capacity  of  his  animals  to 
convert  profitably  large  amounts  of  raw  materials  into  a 
finished  product  of  high  quality. 

Early  maturity 

504.  Definition  of  maturity.  —  Much  stress  is  rightly  laid 
upon  the  importance  of  early  maturity  in  meat  production,  al- 
though the  term  is  used  in  two  more  or  less  distinct  senses. 

Strictly  speaking,  a  mature  animal  is  one  which  has  completed 
its  growth  —  i.e.,  one  in  which  the  increase  of  protein  tissue  has 
reached  its  natural  limit.  In  this  sense,  that  one  of  two  animals 
which  reaches  this  natural  limit  first  is  the  earlier  maturing. 
With  animals  which  reach  substantially  the  same  limit  of  size, 
this  conception  of  early  maturity  is,  of  course,  synonymous 
with  a  greater  absolute  rate  of  protein  growth  (460),  while  if  the 
latter  be  expressed  relatively  to  the  weight  of  the  animal,  as 
in  previous  pages,  the  same  thing  is  true  regardless  of  size. 

The  term  early  maturity,  however,  is  used  also  in  a  quite 
different  sense,  referring  to  the  conformation  of  the  animal  rather 
than  to  completed  growth.  Thus,  if  a  steer  at  22  months  has 
attained  the  typical  beef  form  and  reached  sufficient  size  to 
meet  the  demands  of  the  market,  he  is  said  to  be  mature.  Ob- 
viously, this  does  not  mean  that  he  has  completed  his  growth, 
but  simply  that  he  has  made  sufficient  growth  to  furnish  market- 
able meat.  This  conception  of  maturity,  in  other  words,  is 
commmercial  rather  than  physiological.  It  is  important  to 
note,  however,  that  it  involves  a  physiological  element.  A 
certain  size  of  carcass  as  well  as  a  certain  conformation  is  de- 
manded, and  to  reach  this  at  an  early  age  almost  necessarily 
implies  a  greater  rate  of  growth,  whether  measured  physiologi- 


MEAT  PRODUCTION  429 

cally  by  increase  of  protein  tissue  or  practically  by  gain  in 
weight. 

In  whichever  sense  the  term  maturity  is  used,  however,  the 
matter  reduces  itself  to  the  question  of  rate  of  growth.  The 
greater  the  initial  impulse  to  growth,  the  sooner,  other  things  be- 
ing equal,  will  the  animal  complete  his  growth,  while  if  the  rate 
of  growth  can  be  made  sufficiently  rapid  the  desired  accumula- 
tion of  meat,  and  consequent  weight,  may  be  reached  before 
physiological  maturity.  In  other  words,  the  rate  of  growth  may 
be  looked  upon  as  expressing  the  capacity  of  the  machine,  since, 
as  was  stated  in  Chapter  XI,  it  is  substantially  determined 
by  biological  factors  and  is  apparently  little  affected  by  the  feed 
supply,  provided  only  that  the  latter  is  adequate. 

505.  Economic  significance.  —  There  seems  no  reason  to 
suppose  that  there  is  any  material  difference  as  regards  physio- 
logical economy  between  rapid  growth  and  slow  growth ;  that 
is,  there  is  no  reason  to  suppose  that  the  storing  up  of  certain 
amounts  of  protein  and  energy  in  the  body  of  an  animal  in  one 
month  requires  any  greater  or  any  less  total  feed  supply,  in 
addition  to  the  maintenance  requirement,  than  the  storing  up  of 
the  same  amounts  in  the  two  months'  time,  except  as  heavy 
feeding  may  diminish  the  percentage  digestibility  of  the  ration 
(722).  In  other  words,  it  may  be  assumed  that  if  a  gain  of  one 
pound  in  live  weight  contains  2500  Calories  of  energy,  the  ra- 
tion must  supply  that  amount  of  net  energy  above  the  main- 
tenance requirement  within  the  time  required  to  make  the 
gain,  whether  that  time  be  one  day  or  three. 

From  the  economic  point  of  view,  however,  there  is  a  very 
important  difference  which  explains  the  stress  laid  upon  early 
maturity  in  meat-producing  animals.  It  is  plain  that,  other 
things  being  equal,  the  animal  which  inherits  the  greater  initial 
impulse  to  growth,  and  in  which  that  impulse  dies  out  the  more 
slowly,  will  reach  either  physiological  maturity  or  a  given  size 
and  weight  sooner  than  the  one  in  which  that  impulse  is  less. 
It  makes  a  very  material  difference,  however,  to  the  producer 
of  beef  cattle,  for  example,  whether  a  calf  weighing  100  pounds 
at  birth  has  the  capacity  to  reach  a  weigh  of  1200  pounds  at 
two  years  old,  or  whether  he  requires  three  years  to  do  it.  This 
is  not,  however,  because  there  is  any  material  difference  in  the 
amount  of  feed  which  the  animal  requires  to  manufacture  the 


430  NUTRITION  OF  FARM  ANIMALS 

1 1  oo  pounds  of  increase.  The  difference  as  regards  feed  cost 
comes  in  the  expenditure  for  maintenance,  since  each  pound 
of  gain,  as  well  as  the  original  100  pounds,  must  be  maintained 
from  the  time  it  is  laid  on  until  maturity.  The  animal,  then, 
which  has  the  higher  rate  of  growth  and  which  matures  in 
two  years  costs  the  owner  a  notably  less  expenditure  for  feed 
than  the  one  maturing  in  three  years,  to  say  nothing  of  the 
saving  in  cost  of  attendance  and  in  interest  on  the  investment. 

Age 

506.  Influence  on  cost  of  production.  —  It  is  an  undisputed 
fact  that  gain  is  made  more  rapidly  and  more  cheaply  by  the 
younger  as  compared  with  the  older  animal.     This  is  true  both 
in  growth  proper  and  in  the  commercial  fattening  of  partly 
mature  animals.1 

On  the  other  hand,  it  was  shown  in  Chapter  XI  (472-476)  that 
there  is  no  experimental  evidence  that  the  capacity  of  the  young 
animal  for  making  a  more  rapid  gain  is  due  to  any  greater 
physiological  economy  in  the  conversion  of  surplus  digestible 
material  into  tissue,  while  it  has  also  been  established  (720) 
that  the  digestive  power  of  the  young  animal  is  not  materially 
different  from  that  of  the  mature  animal.  As  regards  protein, 
the  indications  are  that  the  loss  of  nitrogenous  material  in  the 
actual  conversion  of  feed  protein  into  body  protein  is  not  or- 
dinarily great  and  is  no  greater  in  the  old  than  in  the  young 
animal,  while  as  regards  energy  it  was  shown  that  the  proba- 
bilities are  in  favor  of  the  view  that  its  utilization  is  less  rather 
than  greater  in  the  younger  than  in  the  older  animal. 

507.  Causes  of  greater  economy.  —  More  or  less  confusion  of 
thought  has  resulted  from  this  apparent  conflict  of  evidence, 
while  feeding  experiments  like  those  cited  by  Henry  and  Morri- 
son have  been  made  the  basis  of  unwarranted  inferences  as  to 
the  greater  digestive  and  assimilative  powers  of  young  animals. 
This  confusion  has  arisen  to  a  large  degree  through  failure  to 
distinguish   between   physiological   and   commercial   economy 
and  it  is  important  to  secure  a  clear  conception  of  the  elements 
of  the  commercial  superiority  of  the  younger  animal. 

1  Compare  Henry  and  Morrison,  Feeds  and  Feeding,  i5th  Ed.,  pp.  431-434,  512, 
568-572. 


MEAT  PRODUCTION  431 

608.  Difference  in  feeding  stuffs.  —  The  difference  in  the 
character  of  the  feed  consumed  by  the  animal  at  different  ages 
must  not  be  overlooked.  The  very  young  animal  subsists  on 
milk  (or  milk  substitutes).  As  it  grows  older  and  begins  to 
consume  solid  feed,  the  latter  must  be  at  first  of  a  rather  con- 
centrated character  and  highly  digestible  while,  with  advancing 
maturity,  the  ration  is  likely  to  consist  to  an  increasing  extent 
of  coarser  and  more  bulky  materials.  It  is  evident  that  to 
make  a  direct  comparison  between  animals  receiving  such  dif- 
ferent rations  on  the  basis  of  the  dry  matter  of  the  latter  is  to 
ascribe  to  differences  in  the  animals  what  is  really  due  to  differ- 
ences in  the  feed.  The  ration  of  the  younger  animal  will  usually 
have  the  higher  percentage  digestibility,  while  at  the  same 
time  it  may  cause  a  smaller  expenditure  of  energy  in  the  pro- 
cesses of  digestion  and  assimilation,  so  that  the  net  energy  values 
of  the  rations  per  unit  of  dry  matter  are  unequal.  That  an 
animal  shows  a  greater  rate  of  gain  on  milk  than  later  on  a 
mixed  ration  of  grain  and  roughage  does  not  necessarily  show 
that  the  younger  animal  made  any  more  efficient  use  of  the 
materials  actually  resorbed,  but  may  be  simply  because  it  re- 
ceives more  actual  feed  (net  energy)  in  a  unit  of  dry  matter. 

509.  Difference  in  composition  of  gain.  —  It  must  also  be 
remembered  that  the  cheaper  gain  made  by  the  younger  an- 
imal means  gain  in  live  weight  and  that,  as  shown  in  Chapter 
XI  (458),  this  increase  is  of  inferior  food  value  as  compared 
with  that  of  the  more  mature  animal  and  represents  the  storage 
of  less  energy,  since  it  contains  more  water  and  a  larger  pro- 
portion of  protein  to  fat  in  its  dry  matter.     A  greater  increase 
in  live  weight,  even  on  perfectly  comparable  rations,  therefore 
may  be  compensated  for  by  the  lower  quality  of  that  increase. 
Gain  by  the  younger  animal  is,  so  to  speak,  more  dilute. 

510.  Feed   consumption.  —  A    third   important   factor,    es- 
pecially when  the  animal  is  not  pushed  to  the  limit  of  his  capac- 
ity, is  the  relatively  greater  consumption  of  feed  by  the  younger 
animal.     While  the  individual  consumes  more  feed  per  head  as 
it  grows  older,  the  consumption  per  unit  of  live  weight  and  in 
particular  per  unit  of  body  surface  decreases.     For  example, 
in  Henry's  averages  for  swine  and  in  Weiske's  experiments  on 
growing  lambs  cited  in  Chapter  XI  (481  b,  487),  the  total  feed 
consumption  was :  — 


432  NUTRITION  OF  FARM  ANIMALS 

TABLE  109.  —  RELATION  OF  WEIGHT  OF  PIGS  TO  FEED  CONSUMED 


DAILY  FEED 

Per  too  Lb.  Live  Weight 

RANGE  OF  WEIGHT 

AGE  WEIGHT 

Per  Day 

In  Proportion 
to  Weight 

In  Proportion 
to  Surface 

Pounds 

Pounds 

Pounds 

Pounds 

Pounds 

15  to    50 

38 

2.2 

6.0 

4-9 

50  to  100 

78 

3-4 

4-3 

100  to  150 

128 

4.8 

3-8 

150  tO  2OO 

174 

5-9 

3-5 

2OO  tO  25O 

226 

6.6 

2.9 

250  to  300 

271 

7-4 

2.7 

300  to  350 

320 

7-5 

2.4 

3-45 

TABLE  no.  —  FEED  CONSUMPTION  BY  LAMBS 


LIVE  WEIGHT 

DIGESTIBLE  ORGANIC  MATTER 
EATEN  PER  50  KGS.  LIVE 
WEIGHT 

In  Proportion 
to  Weight  ' 

In  Proportion 
to  Surface 

Period  I     

Kgs. 
20.5 

25-5 
28.9 
32.6 
35-0 

35-3  . 
38.0 

40-5 
39-o 

57-5 

Grams 

1059 
1029 
870 
850 
757 
755 
710 
681 
690 
549 

Grams 

787 

575 

Period  II    
Period  III       .... 

Period  IV  

Period  V 

Period  VI       

Period  VII      
Period  VIII 

Period  IX  

Period  X    . 

But  the  maintenance  requirement  is  approximately  propor- 
tional to  the  body  surface.  Consequently  the  feed  consump- 
tion as  the  animal  grows  older  does  not  keep  pace  with  the  in- 
crease in  its  maintenance  requirement,  so  that  a  constantly 
diminishing  proportion  of  its  feed  is  available  for  productive 
purposes.  For  example,  in  Periods  I  and  X  respectively  of 
Weiske's  experiment  it  may  be  computed  that  the  metaboliz- 


MEAT  PRODUCTION  433 

able  energy  of  the  rations  consumed  and  the  approximate 
maintenance  requirements  per  day  and  head  were :  — 

TABLE  m.  —  DIMINISHING  AVAILABILITY  OF  FEED 


METABOLIZABLE  ENERGY 

PERIOD  I 

PERIOD  X 

In  ration 

1568  Cals 

2209  Cals 

Required  for  maintenance   

807  Cals. 

1613  Cals. 

Available  for  gain  ...          .... 

761  Cals. 

qo6  Cals. 

In  Period  I,  48.5  per  cent  of  the  metabolizable  energy  of  the 
ration  was  available  for  growth  as  compared  with  only  27  per 
cent  in  Period  X. 

In  brief,  then,  the  undisputed  superiority  of  the  young  animal 
as  regards  -the  amount  of  feed  required  to  produce  a  unit  of 
increase  may  be  reasonably  ascribed :  - 

First,  to  the  fact  that  his  feed  is  often  of  a  more  concentrated 
nature,  containing  a  greater  proportion  of  digestible  matter  and 
perhaps  causing  a  smaller  expenditure  of  energy  in  connection 
with  its  digestion  and  assimilation. 

Second,  to  the  fact  that  the  gain  of  live  weight  in  the  young 
animal  contains  a  less  percentage  of  dry  matter  and  especially 
of  fat  and  therefore  represents  the  storage  of  less  energy  than 
the  same  increase  in  the  older  animal. 

Third,  that  the  total  feed  consumption  of  the  animal,  espe- 
cially upon  the  more  bulky  feeds  generally  used  for  simple 
growth,  may  not  increase  as  rapidly  as  the  maintenance  re- 
quirement, so  that  an  increasing  proportion  of  the  feed  is 
required  simply  for  maintenance  and  is  unavailable  to  produce 
increase. 

511.  Production  of  lean  meat.  —  The  difference  in  the  nature 
of  the  gain  made  at  different  ages  which,  as  has  just  been  shown, 
is  a  material  factor  in  determining  the  cost  of  gain  in  live  weight, 
is  of  even  greater  importance  in  another  aspect  of  the  matter. 

As  shown  in  Chapter  XI  (460-463),  the  capacity  for  growth 
in  the  stricter  sense, i.e.,  for  increase  of  protein  tissue,  is  especially 
characteristic  of  the  young  animal  and  decreases  rapidly  as  he 
grows  older,  while  it  does  not  appear  that  it  can  be  materially 

2  F 


434 


NUTRITION  OF  FARM  ANIMALS 


stimulated  by  the  protein  supply  in  the  feed.  It  is  of  the  high- 
est- economic  importance,  therefore,  to  utilize  to  the  full  the 
ability  of  the  young  animal  to  lay  on  protein  tissue.  In  the  early 
stages  of  growth,  he  is  able  to  utilize  a  relatively  abundant  supply 
of  feed  protein  which,  if  given  to  an  older  animal,  would  largely 
undergo  protein  katabolism  and  be  lost  so  far  as  growth  is 
concerned,  while  at  the  same  time  the  total  feed  per  head  re- 
quired for  maintenance  is  smaller.  The  feeder  cannot  afford 
to  stint  the  protein  supply  of  the  young  animal,  while  the 
earlier  the  process  of  growth  can  be  completed  or  approach 
nearly  enough  to  completion  to  satisfy  market  demands,  the 
more  economically  will  it  be  conducted. 

The  conclusions  regarding  the  rate  of  increase  of  protein 
tissue  considered  in  Chapter  XI  are,  however,  derived  chiefly 
from  determinations  of  the  gain  or  loss  of  total  nitrogenous 
matter,  including,  besides  the  edible  portion,  the  protein  of  the 
skin,  hair,  hoofs,  horns  and  other  epidermal  tissue,  of  the  in- 
ternal organs  and  of  the  skeleton.  It  is  important,  therefore, 
to  inquire  into  the  rate  of  increase  of  the  edible  portion  of  the 
carcass. 

TABLE  112.  —  GAIN  OF  FAT-FREE  LEAN  MEAT  AND  TOTAL  PROTEIN  BY 

LAMBS 


GAIN  P 

ER  WEEK 

AVER- 
AGE 

AND 

HEAD 

LOT 

PERIOD 

LENGTH 

OF 

PERIOD 

CHARACTER 
or  RATION 

AGE 

OF 

ANI- 

Fresh 
Fat- 
free 

Total 
Dry 
Protein 

MALS 

Meat 

(Esti- 

mated) 

Kilo- 

Kilo- 

Days 

Days 

grams 

grams 

[I  and  II 

203 

Growing 

290 

0.114 

0.056 

i    

J    TTT            J    TT  7" 

1  III  and  IV 

259 

Lrrowmg 

52l 

•053 

.031 

IV 

175 

Fattening 

745 

.042 

.029 

2     

f  I  and  II 

189 

Fattening 

290 

.130 

.077 

[HI 

147 

Fattening 

458 

.040 

.026 

While  it  may  be  fairly  assumed  that  the  increase  of  edible  meat 
will  be  in  a  general  way  proportional  to  the  increase  of  total  protein, 
it  is  equally  clear  that  there  may  be  considerable  departures  from 
the  average.  Unfortunately,  however,  the  data  upon  this  point  are 


MEAT  PRODUCTION 


435 


scanty,  owing  to  the  laborious  and  expensive  nature  of  such  experi- 
ments. About  the  only  results  available  are  those  of  Kern  and 
Wattenberg  on  lambs  and  those  of  Jordan  on  steers,  that  is,  these  are 
the  only  ones  which  permit  of  a  comparison  of  the  rate  of  growth  of 
similar  animals  in  successive  periods.  Both  these  experiments  have 
been  outlined  in  Chapter  XI  (458) .  Table  112  shows  the  gain  of  fat- 
free  lean  meat  in  Kern  and  Wattenberg's  experiments  as  compared 
with  the  estimated  gains  of  total  protein.  The  term  "meat"  refers 
only  to  the  meat  of  the  "butcher's  pieces,"  freed  from  sinews  and 
coarser  connective  tissue  by  passage  through  a  meat  grinder.  The 
production  of  fat-free  lean  meat  was,  in  general,  parallel  to  that  of 
total  protein,  diminishing  with  advancing  maturity.  Apparently, 
however,  the  rate  of  gain  of  total  protein  diminished  less  rapidly  than 
that  of  edible  meat. 

Jordan's  experiments  include  a  comparison  of  the  weights  and 
chemical  composition  of  two  pairs  of  animals  at  the  end  of  twenty- 
seven  months'  and  seventeen  months'  feeding  respectively.  The  pro- 
tein of  the  lean  meat  after  mechanical  separation  from  the  fat  tissue, 
and  the  total  body  protein,  were  as  follows :  — 

TABLE  113.  —  GAIN  OF  PROTEIN  BY  CATTLE 


No.  OF  ANIMAL 

AVERAGE  AGE 

PROTEIN  OF 
LEAN  MEAT 

TOTAL  PROTEIN 
OF  BODY 

Pounds 

Pounds 

2 

32  months 

42.13 

167.94 

I 

22  months 

37-96  l 

136.30 

Gain  in  10  months 

4.17 

31.64 

Gain  per  day 

.0128 

.0971 

3 

32  months 

43-24 

161.38 

4 

22  months 

35-08 

126.30 

Gain  in  10  months 

8.16 

35-08 

Gain  per  day 

.0261 

.1123 

So  far  as  conclusions  can  be  safely  drawn  from  these  few 
results,  it  would  appear  that  the  rate  of  gain  of  lean  meat  runs 
parallel  to  that  of  total  protein  and  like  the  latter  diminishes 
with  age,  the  diminution  being  somewhat  more  rapid  in  the  for- 
mer case  than  in  the  latter.  At  all  ages  the  storage  of  total 

1  Nos.  i  and  4  were  somewhat  lighter  animals  than  Nos.  2  and  3.  The  protein 
content  has  been  computed  to  the  live  weight  of  the  heavier  animal  in  each  case. 


436  NUTRITION  OF  FARM  ANIMALS 

protein  (or,  more  exactly,  the  increase  in  the  fat-free  body) 
considerably  exceeds  the  gain  of  lean  meat  proper  and  with  in- 
creasing maturity  this  difference  seems  to  become  relatively 
greater. 

512.  Best  age  for  fattening.  —  While  meat  production  in 
the  narrower  sense  of  increase  of  protein  tissue  is  confined  to 
the  immature  animal,  the  improvement  of  its  quality  by  the 
fattening  process  is  an  essential  part  of  commercial  meat  pro- 
duction. Fattening,  however,  may  be  effected  at  practically 
any  time  in  the  life  of  the  animal.  Assuming  that  an  animal 
is  to  be  in  the  hands  of  the  same  owner  from  birth  until 
slaughter,  at  what  stage  should  the  distinctively  fattening 
process  as  distinguished  from  growth  be  begun? 

It  is  evident  that  the  beginning  of  the  fattening  process  may 
be  delayed  too  long.  To  take  the  extreme  case,  it  would  be 
obviously  uneconomical  first  to  grow  an  animal  to  full  maturity 
and  then  to  add  a  fattening  period.  While  there  is  no  reason 
to  suppose  that  the  amount  of  feed  actually  expended  in  the 
production  of  a  unit  of  fat  would  be  materially  greater  than  if  the 
fattening  were  conducted  during  the  latter  part  of  the  growing 
period,  the  expenditure  for  maintenance,  care,  interest,  etc., 
would  be  simply  so  much  added  to  the  cost  of  production.  On 
the  other  hand,  heavy  fattening  rations,  containing  large  amounts 
of  non-nitrogenous  nutrients,  even  if  they  do  not  interfere  with 
the  growth  of  young  animals,  are  uneconomical,  tending  either 
to  overload  the  meat  with  fat  or  toward  the  accumulation  of 
cheap  internal  fat,  and  making  the  animal  ripe  for  the  butcher 
before  his  capacity  for  producing  lean  meat  has  been  properly 
utilized.  A  limited  market  exists,  of  course,  for  fat  lambs  and 
veals;  but  for  the  production  of  the  world's  meat  supply  it  is 
important  to  utilize  the  capacity  for  growth  up  to  a  point  at 
least  approaching  maturity.  Too  early  fattening  tends  to 
produce  an  animal  which,  even  if  not  of  inferior  quality,  must 
be  maintained  in  a  fat  condition  until  the  growth  of  lean  meat 
has  had  an  opportunity  to  overtake  that  of  fat.  Plainly  the 
beginning  of  the  fattening  should  be  so  timed  that  it  will  be 
completed  by  the  time  the  rate  of  gain  of  lean  meat  ceases  to  be 
profitable  under  the  existing  market  conditions. 

The  period  in  the  life  of  the  animal  at  which  fattening  should 
begin,  then,  will  depend  upon  its  inherited  capacity  for  growth, 


MEAT  PRODUCTION  437 

i.e.,  its  rate  of  growth  as  defined  on  previous  pages.  If  this  is 
rapid,  as,  for  example,  in  the  improved  breeds  of  swine  especially 
and  to  a  somewhat  less  extent  with  cattle  and  sheep,  it  may  be 
practicable  to  begin  the  fattening  almost  from  birth,  the  innate 
tendency  to  growth  assuring  sufficient  size  and  weight  by  the 
time  good  marketable  condition  is  attained.  To  secure  this 
result,  however,  it  is  necessary  to  use  rations  containing  large 
amounts  of  easily  digestible  feed  in  a  small  bulk  and  such 
rations  are  necessarily  comparatively  expensive.  Moreover, 
growth  as  well  as  fattening  requires  an  expenditure  of  feed 
energy,  and  as  appeared  in  Chapter  XI  (473-476)  a  not  incon- 
siderable one.  The  capacity  of  an  animal  to  consume  feed,  how- 
ever, is  limited  and  when  a  relatively  young  animal  is  put  on 
full  feed,  the  more  growth  he  makes  the  less  feed  will  remain  for 
fattening.  This  corresponds  with  the  experience  of  practical 
feeders  that  mature  animals  will  reach  a  higher  condition  in  a 
given  time  than  the  young  ones. 

Under  present  economic  conditions,  as  a  rule,  only  the  best 
grade  of  animals  having  to  a  high  degree  the  quality  of  early 
maturity  can  be  profitably  handled  in  the  way  just  indicated. 
With  animals  inferior  in  this  respect,  the  more  economical  pro- 
cedure usually  is  a  period  of  growth  upon  comparatively  cheap 
rations,  consisting  to  a  considerable  extent  of  roughage,  followed 
by  a  relatively  short  period  of  intensive  fattening,  beginning, 
however,  before  the  capacity  for  growth  has  been  entirely  lost. 
The  economy  lies,  of  course,  in  the  possibility  of  supporting 
growth  and  maintenance  upon  relatively  cheap  feeds  during 
the  longer  time  necessary  in  the  case  of  inferior  animals  and 
will  depend  to  a  large  extent  upon  the  relative  costs  of  feeding 
stuffs.  The  actual  feed  cost  of  the  fattening  itself  is  likely  to 
be  about  the  same  in  either  case. 

For  the  individual  who  raises  and  fattens  his  own  animals, 
then,  it  would  appear  to  be  economical,  so  far  as  the  feed  cost 
is  concerned,  to  use  as  early  maturing  animals  as  possible  and 
to  push  them  so  as  to  fit  them  for  market  at  as  early  an  age 
as  they  are  capable  of. 

When,  however,  as  is  notably  the  case  in  beef  production,  the 
rearing  of  animals  and  their  fattening  for  market  are  in  dif- 
ferent hands,  other  important  economic  considerations  enter 
in  to  modify  this  conclusion.  In  this  case  the  business  of 


438  NUTRITION  OF  FARM  ANIMALS 

the  feeder  is  substantially  to  enhance  the  quality  of  the 
meat,  and  the  profit  of  the  transaction  depends  to  a  consider- 
able extent  upon  the  difference  between  buying  and  selling 
prices,  and  includes  a  large  element  of  speculation.  While  it 
is  true  that  the  animal  which  still  retains  more  or  less  capacity 
for  growth  will  make  the  cheaper  gains,  nevertheless,  if  the 
market  price  of  such  animals  is  relatively  high  compared  with 
that  of  more  mature  animals  it  may  be  more  profitable  as  a 
business  proposition  to  feed  older  animals,  even  though  the 
feed  cost  per  pound  of  gain  is  higher. 

Condition 

513.  Decreasing  gains  in  fattening.  —  It  is  generally  admitted 
that  in  the  case  of  the  nearly  mature  fattening  animal  the  rate 
of  gain  in  live  weight  decreases  as  the  fattening  progresses  until 
a  limit  is  reached  beyond  which  the  increase,  if  obtained  at  all, 
is  slow  and   very   costly.     Several  causes  are  responsible  for 
this :  - 

First,  the  maintenance  requirement  of  the  animal  increases 
with  its  gain  in  weight  (393).  The  capacity  of  the  digestive 
organs,  however,  undergoes  no  corresponding  increase,  and 
consequently  the  amount  of  excess  feed  is  correspondingly  re- 
duced and  its  proportion  in  the  ration  made  less,  so  that  the 
total  feed  requirement  per  unit  of  gain  will  be  greater. 

Second,  the  appetite  of  well-fattened  animals  not  infrequently 
diminishes,  resulting  in  a  lessened  consumption  of  feed.  This 
again  has  a  double  effect,  diminishing  the  total  amount  of  excess 
feed  available  and  reducing  the  ratio  of  excess  feed  to  total  feed. 

Third,  a  unit  gain  in  live  weight  toward  the  close  of  the 
fattening  period  represents  a  larger  storage  of  energy  than  the 
same  gain  at  the  beginning  (452). 

514.  Effect  on  economy  of  gain.  —  For  all  these  reasons  it 
is  natural  that  the  "  condition  "  of  the  animal  —  that  is,  its 
state  of  fatness  —  should  have  a  marked  effect  on  the  rate  and 
economy  of  gain.     Georgeson 1  reports  the  following  results 
for  a  lot  of  3-year-old  grade  Shorthorn  steers,  the  number  of 
days  stated  in  the  table  meaning  in  each  case  the  number  from 
the  beginning  of  the  feeding :  — 

1  Kansas  Expt.  Sta.,  Bui.  34,  p.  95. 


MEAT  PRODUCTION  439 

TABLE  114.  —  GRAIN  CONSUMED  BY  STEERS  PER  POUND  OF  GAIN 


NUMBER  OF  DAYS  FED 


GRAIN  CONSUMED 

PER  POUND  OF 

GAIN 


112 

140 
i68 
182 


Pounds 

8.07 
8.40 
9-OI 
9.27 
10.00 


Henry  :  reports  the  following  similar  results  for  fattening 
swine :  — 

TABLE  115.  —  INFLUENCE  OF  LENGTH  OF   FATTENING  PERIOD  ON    THE 
FEED  CONSUMPTION  AND  GAIN  OF  HOGS 


FEED  FOR  100  POUNDS 

AVERAGE 
WEIGHT 

AVERAGE 
WEEKLY 
GAIN 

FEED 
EATEN 

DURING 

WEEK  PER 

OF  GAIN 

By  Four- 

HOG 

By  Weeks 

Week 

Periods 

Pounds 

Pounds 

Pounds 

Pounds 

Pounds 

First  week  .... 

222 

11.4 

4i 

362 

Second  week    .     .     . 

235 

13-3 

48 

362 

418 

Third  week      .     .     . 

246 

10.5 

50 

475 

Fourth  week   .     .     . 

257 

10.7 

50 

473 

Fifth  week       .     .     . 

270 

13-9 

51 

368 

* 

Sixth  week      .     .     . 

28l 

IO.I 

5i 

5io 

461 

Seventh  week       .     . 

2Q4 

13-1 

5i 

39i 

Eighth  week    .     .     . 

303 

8.9 

51 

572 

Ninth  week     .     .     . 

313 

10.5 

52 

499 

Tenth  week     .     .    ". 

322 

8.9 

52 

587 

559 

Eleventh  week     .     . 

332 

9.6 

52 

549 

Twelfth  week  .     .     . 

340 

8.8 

52 

598 

On  the  other  hand,  Mumford,2  in  large-scale  feeding  experi- 
ments with  cattle,  has  failed  to  note  any  such  marked  diminution 

1  Feeds  and  Feeding,  loth  Ed.,  p.  510.  2  mSi  Expt.  Sta.,  Bui.  103,  p.  57. 


440  NUTRITION  OF  FARM  ANIMALS 

of  the  gain  during  the  later  stages  of  feeding  as  had  been  generally 
found  by  other  experimenters. 

There  is  no  sufficient  evidence  on  record  to  show  whether  or 
not  the  actual  percentage  utilization  of  the  excess  feed  dimin- 
ishes with  the  advance  of  fattening. 

Breed  and  Individuality 

That  both  those  inherited  qualities  which  characterize  the 
recognized  meat  breeds  and  the  individual  differences  between 
single  animals  are  important  factors  in  the  economy  of  meat 
production  is  generally  recognized.  It  is  a  fact  of  common 
observation  that  marked  differences  exist  between  individual 
animals  as  regards  the  return  which  they  yield  for  the  feed  con- 
sumed, but  the  reasons  for  these  differences  have  not  always  been 
clearly  seen,  and  in  particular  there  has  been  a  tendency  to 
assign  them  to  physiological  causes,  such  as  difference  in  di- 
gestive or  assimilative  power,  and  some  unwarranted  con- 
clusions on  these  points  have  gained  currency. 

615.  Digestive  power.  —  The  superiority  of  one  breed  or 
animal  over  another  as  regards  feeding  capacity  is  often  as- 
cribed to  a  difference  in  the  extent  to  which  the  feed  is  digested, 
although  those  who  make  this  assertion  often  understand  by 
digestion  what  is  more  properly  termed  "  utilization."  Un- 
doubtedly there  are  differences  in  digestive  power  between 
different  animals,  but  except  in  the  case  of  manifestly  ab- 
normal animals  they  have  been  found  to  be  comparatively 
slight  and  'quite  insufficient  to  account  for  the  marked  differ- 
ences in  production  (718,  719).  Neither  is  there  any  evidence 
that  the  improved  breeds  of  meat-producing  animals  possess 
any  superiority  in  this  respect  over  the  ordinary  unimproved 
animals. 

An  illustration  of  the  latter  fact  is  afforded  in  experiments  by 
Armsby  and  Fries,1  in  which  no  material  difference  was  observed  in 
the  digestive  powers  of  a  pure-bred  beef  animal  and  a  " scrub"  at 
the  approximate  ages  of  one,  two  and  three  years.  The  same  experi- 
ments also  failed  to  show  any  material  differences  in  the  losses  of 
energy  in  urine  and  methane,  so  that  the  percentage  of  the  feed 
energy  which  was  metabolizable,  especially  when  computed  on  the 

1  U.  S.  Dept.  of  Agr.,  Bur.  Anim.  Indus.,  Bui.  128  (1911). 


MEAT  PRODUCTION 


441 


energy  of  the  digested  matter,  was  substantially  the  same  for  the  two 
animals.  The  figures  for  the  digestibility  of  the  dry  matter  and  for 
the  percentage  of  the  digestible  energy  metabolizable,  each  being  the 
average  of  two  periods,  were  as  follows :  — 

TABLE  116. —  DIGESTIBILITY  BY  PURE-BRED  AND  SCRUB  STEERS 


• 

TIMOTHY  HAY 

GRAINS 

Steer  A 

Steer  B 

Steer  A 

Steer  B 

Pure-bred 

"  Scrub" 

Pure-bred 

"Scrub" 

Digestibility 

of  dry  matter 

frf 
70 

% 

% 

% 

Experiment  of 

1905     .... 

52.8 

54-9 

66.1 

66.5 

Experiment  of 

1906     .... 

53-7 

55-5 

81.4 

80.4 

Experiment  of 

1907     .... 

62.0 

61.4 

77-8 

78.8 

Percentage    of 

digested    energy 

metabolizable 

Experiment  of 

1905     .     .     .     < 

79.91 

80.07 

8i.53 

80.97 

Experiment  of 

1906     .... 

79.88 

79-57 

81.99 

81.41 

Experiment  of 

1907     .... 

78.75 

77.92 

8i.73 

78.95 

516.  Assimilative  power.  —  This  term  may  be  used  to 
designate  broadly  the  ability  of  the  organism  to  convert  the 
digested  nutrients  of  the  feed  into  body  tissue.  Is  the  good 
meat  producer  able  to  form  from  a  unit  of  digested  feed  of  a 
given  kind  more  new  tissue  than  can  the  inferior  animal?  In 
other  words,  is  the  net  energy  value  of  the  feed  affected  by  the 
individuality  of  the  animal?  As  yet  there  has  been  scarcely 
any  scientific  investigation  bearing  upon  this  question,  but 
such  evidence  as  is  available  does  not  indicate  the  existence 
of  material  differences  in  this  respect. 

Such  of  Kelmer's  determinations  of  net  energy  values  for  fatten- 
ing (449)  as  were  made  upon  similar  feeding  stuffs  with  different 
animals  show  a  generally  good  agreement  as  regards  the  utilization 
of  the  energy  of  the  feed,  although  it  does  not  appear  from  the  ac- 
counts of  the  experiments  whether  or  not  the  animals  used  differed 
materially  in  type. 

The  experiments  by  Armsby  and  Fries,  just  referred  to,  were  directed 
more  specifically  to  the  investigations  of  this  question.  They  failed 
to  demonstrate  any  decided  advantage  on  the  side  of  the  pure-bred 


442  NUTRITION  OF  FARM  ANIMALS 

animal  so  far  as  the  percentage  utilization  of  the  energy  supplied  in 
excess  of  the  maintenance  requirement  was  concerned,  the  slight 
difference  observed,  especially  in  the  earlier  years,  being  perhaps 
accounted  for  by  the  greater  tendency  of  the  pure-bred  -steer  to 
lay  on  fat. 

In  the  aggregate  a  considerable  number  of  breed  tests  of  cattle, 
sheep  and  swine  have  been  made  by  the  American  experiment  stations, 
the  results  of  some  of  which  have  been  summarized  by  Henry  1  so  as 
to  show  the  quantity  of  feed  consumed  per  unit  of  gain.  While  in 
individual  cases  considerable  fluctuations  are  to  be  found,  neverthe- 
less, the  results  as  a  whole  certainly  fail  to  indicate  any  marked  su- 
periority of  one  breed  over  another  in  this  respect,  and  later  experi- 
ments have  not  given  materially  different  results.  When  we  come  to 
consider  the  other  possible  factors,  such  as  differences  in  live  weight, 
in  maintenance  requirement,  in  total  feed  consumed,  etc.,  we  must 
conclude  that  the  recorded  results  give  no  clear  evidence  of  any 
specific  individual  or  breed  differences  in  the  actual  physiological 
processes  involved  in  the  conversion  of  feed  into  tissue,  although  it  is 
equally  true,  of  course,  that  they  fail  to  prove  the  absence  of  such 
differences. 

It  seems  clear  that  it  is  necessary  to  look  elsewhere  than  to 
a  supposed  greater  digestive  and  assimilative  capacity  of  the 
typical  meat-producing  animal  for  an  explanation  of  his  eco- 
nomic superiority  over  the  less  specialized  individual. 

517.  The  maintenance  requirement.  —  It  was  shown  in 
Chapter  VIII  (376, 391)  that  not  inconsiderable  differences 
may  exist  between  different  individuals  as  regards  the  main- 
tenance requirement.  Thus  in  the  case  of  cattle  the  extreme 
figures  of  4.72  Therms  and  7.43  Therms  of  net  energy  per  1000 
pounds  live  weight  were  observed  for  thin  animals.  Of  the 
various  factors  affecting  the  maintenance  requirement,  it  was 
pointed  out  that  one  of  the  most  important  is  the  degree  of 
muscular  activity  of  the  animal  even  when  in  the  state  of  so- 
called  rest,  and  the  decidedly  lower  maintenance  requirement 
found  by  Armsby  and  Fries  for  a  pure-bred  beef  steer  as  com- 
pared with  a  scrub  was  there  interpreted  as  probably  due  to 
the  more  nervous  disposition  and  greater  restlessness  of  the 
latter. 

It  is  clear,  however,  that  of  two  animals  receiving  identical 
rations  the  one  which  has  the  lower  maintenance  requirement 

1  Feeds  and  Feeding,  zoth  Ed.,  pp.  328  and  511. 


MEAT  PRODUCTION  443 

will  have  the  larger  surplus  for  growth  or  fattening  and,  other 
things  being  equal,  will  make  the  greater  increase  per  unit  of 
total  feed.  To  what  extent  a  lower  maintenance  requirement 
is  characteristic  of  high-bred  meat-producing  animals  remains 
to  be  determined.  If  it  appears  to  be  a  general  fact,  it  would 
go  far  toward  explaining  any  superiority  on  the  part  of  the  latter. 
It  is  not  impossible,  also,  that  differences  in  the  amount  of 
muscular  activity  may  play  a  more  important  part  in  fattening 
than  in  the  experiments  on  maintenance  hitherto  reported.  In 
the  latter,  the  experimental  conditions  necessitated  consider- 
able restriction  of  the  freedom  of  motion,  while  under  the  con- 
ditions of  practice  a  wider  scope  may  perhaps  be  afforded  to 
the  individuality  of  the  animal  in  this  respect. 

518.  Feed   consumption.  —  Another   important   element   of 
individual  superiority  is  the  ability  of  an  animal  to  consume 
regularly  large  amounts  of  feed.     Of  two  animals  otherwise 
similar,  it  is  clear  that  the  one  which  is  able  to  consume  day 
after  day  the  heavier  ration  is  the  better  meat  producer.     It  is 
not  always  realized,  however,  that  the  heavier  feeder  makes  a 
relatively  more  profitable  use  of  his  feed  because,  as  pointed 
out  in  Chapter  VIII  (360),  assuming  the  maintenance  require- 
ment to  be  the  same,  the  productive  part  of  the  ration  forms  a 
larger  part  of  the  total  ration  in  the  case  of  the  large  eater. 
Consequently,  since  all  the  feed  must  be  paid  for,  this  animal 
makes  the  more  economical  gain,  not  because  he  utilizes  his 
excess  feed  better  but  simply  because  he  is  able  to  consume 
more  of  it. 

There  are  doubtless  marked  differences  between  individual 
animals  in  this  respect.  Whether  the  specific  meat-producing 
breeds  as  a  whole  possess  any  advantage  in  this  respect  appears 
doubtful  in  view  of  the  results  on  record  regarding  the  feed  cost 
of  gain  with  different  breeds.  Apparently  the  quality  is  one 
to  which  the  attention  of  breeders  has  not  been  specially  di- 
rected, yet  it  is  one  which,  it  would  seem,  might  well  repay 
attention. 

519.  Type  and  conformation.  —  It  is  a  well-recognized  fact 
that  the  conformation  of  a  meat  animal  is  a  very  important 
factor  in  determining  his  selling  price.     The  improved  meat 
breeds  as  a  rule  show  a  higher  ratio  of  dressed  to  live  weight, 
a  better  distribution  of  fat  in  the  finished  carcass,  a  somewhat 


444  NUTRITION  OF  FARM  ANIMALS 

larger  proportion  of  the  higher  priced  cuts  and  a  higher  quality 
of  meat.  They  are  all  important  factors  in  the  economic  pro- 
duction of  meat,  but  there  is  no  evidence  that  their  possession 
renders  an  animal  any  more  efficient  as  a  converter  of  feed  into 
meat. 

520.  Early  maturity.  —  The  economic  importance  of  a  rapid 
rate  of  growth  and  of  the  consequent  early  maturity  has  been 
considered  in  previous  paragraphs  (504,  505). 

It  is  a  matter  of  common  experience  that  there  exist  marked 
differences  between  individuals  of  the  same  species  both  as  to 
the  weight  finally  attained  by  the  mature  animal  and  as  to  the 
rate  of  growth  at  the  same  age.  It  is  natural  to  interpret  this 
fact  as  indicating  corresponding  individual  differences  in  the 
rate  of  growth,  especially  of  protein  tissue,  but  the  writer  is 
not  aware  of  any  recorded  experiments  bearing  specifically  on 
this  point.  It  is  true  that  the  quality  of  early  maturity  is 
popularly  attributed  to  the  meat  breeds,  but  as  regards  cattle 
at  least  Henry  1  has  shown  that  the  data  at  hand  fail  to  prove 
that  the  beef  breeds  as  such  show  a  greater  rate  of  gain  in  live 
weight  or  a  greater  weight  at  maturity  than  do  the  dairy  breeds, 
although  it  is  likewise  true  that  other  elements  than  simply 
the  weight  enter  into  the  economic  conception  of  maturity. 
If  it  is  correct  to  ascribe  the  individual  differences  noted  above 
to  variations  in  the  rate  of  growth  of  protein  tissue,  it  sug- 
gests a  field  for  investigation  of  much  interest  both  to  the 
breeder  and  the  feeder. 

§  3.  FEEDING  FOR  MEAT  PRODUCTION 

521.  Feeding  as  related  tojndividuality.  —  The  facts  consid- 
ered in  the  previous  section  relate  to  the  capacity  of  the  animal 
as  a  mechanism  for  the  conversion  of  vegetable  products  into 
meat.     They   (and  other  less  important  ones)    determine  the 
degree  to  which,  from  the  commercial  standpoint,  the  animal 
is  able  to  utilize  the  feed  given  it.     Favorable   modifications 
of  any  of  these  factors  are  of  advantage  because  they  enable  a 
larger  and  more  profitable  production  to  be  secured. 

Feeding  stands  in  a  somewhat  different  relation,  in  that  its 
purpose  is  to  supply  the  material  upon  which  the  mechanism 

1  Feeds  and  Feeding,  loth  Ed.,  p.  329. 


MEAT  PRODUCTION  445 

works.  It  is  of  prime  importance  to  the  feeder  that  his  animals 
shall  have  the  largest  possible  productive  capacity,  but  while 
the  maximum  which  the  animal  can  produce  is  determined  by 
its  breed  and  individual  characteristics  and  cannot  be  materially 
affected  by  feeding,  the  amount  which  it  actually  does  produce 
in  any  given  case  must  depend  upon  the  amount  of  material 
supplied  to  it  in  its  feed.  Production  may  be  limited  by  a 
deficient  feed  supply,  although  it  cannot  be  forced  above  a  cer- 
tain maximum  by  increasing  the  ration. 

522.  Feed  requirements.  —  Since  feed  is  to  be  looked  upon 
as  a  supply  of  raw  material  for  the  animal  mechanism,  it  is  clear 
that  the  kind  and  amount  required  will  depend  primarily  upon 
the  capacity  of  the  animal.     The  young  animal,  with  his  marked 
capacity  for  growth,  will  require  relatively  more  of  the  specific 
materials  for  growth,  viz.,  protein  and  ash,  than  will  the  older 
animal.     The  early  maturing  animal,  with  his  greater  rate  of 
growth,  will  require  more,  total  feed  per  day  than  the  one  ma- 
turing more  slowly.     The  animal  with  the  capacity  to   con- 
sume and  utilize  large  total  amounts  of  feed  must  be  given  these 
larger  amounts  in  order  that  his  advantage  in  this  respect 
may  be  fully  utilized. 

As  already  pointed  out,  meat  production  is  a  combination  of 
growth  and  fattening,  the  latter  process  being  superimposed 
upon  the  former.  The  feed  requirements  of  the  meat-producing 
animal,  therefore,  include  in  the  first  place  the  requirements  for 
normal  growth,  to  which  are  added  during  a  longer  or  shorter 
time  according  to  circumstances  the  requirements  for  the  pro- 
duction of  fat.  The  feed  requirements  for  these  two  purposes 
have  already  been  considered  in  the  two  previous  chapters,  but 
may  be  conveniently  recapitulated  here  with  more  particular 
emphasis  on  economic  relations. 

Protein  requirements  for  meat  production 

523.  Relation  to  age.  —  It  was  shown  in  Chapters  X  and  XI 
that  it  is  only  during  growth  that  any  considerable  production 
of  meat  in  the  narrower  sense,  i.e.,  of  muscular  tissue,  takes 
place,  and  likewise  that  the  energy  of  growth  is  greatest  in  the 
young  animal  and  diminishes,  at  first  rapidly  and  then  more 
and  more  slowly,  until  physiological  maturity,  when  but  a  slight 


446  NUTRITION  OF  FARM  ANIMALS 

increase  of  the  total  protein  and  still  less  of  meat  proper  can  be 
secured.  Evidently  the  question  of  the  necessary  protein  supply 
in  the  rations  of  meat-producing  animals  is  of  special  impor- 
tance during  the  early  stages  of  growth. 

524.  Minimum  protein  supply  for  growth.  —  The  meat-pro- 
ducing animal,  then,  in  order  to  utilize  fully  his  capacity  for 
growth  must  be  supplied  in  his  feed  at  each  stage  of  that  growth, 
in  addition  to  his  maintenance  requirement,  with  at  least  as 
much  digestible  protein  as  he  is  capable  of  storing  up  in  his 
growth.     Whether  any  greater  quantity  than  this  is  necessary 
or  advantageous  is,  as  has  been  shown  (491),  still  to  some  de- 
gree an  unsettled  question.     Some  experiments,  especially  with 
cattle  and  sheep,  indicate  that  any  considerable  surplus  is  un- 
necessary for  normal  growth,  while,  on  the  other  hand,  feeding 
experiments  with  pigs  and  to  some  extent  with  ruminants  indi- 
cate that  amounts  considerably  in  excess  of  those  thus  com- 
puted assure  at  least  greater  gains  of  live  weight. 

525.  Protein  requirements    in    fattening.  —  While    growth 
and  fattening  may  be  regarded  physiologically  as  distinct  pro- 
cesses, it  is  economically  important  in  the  practice  of  meat  pro- 
duction that  they  should  go  on  more  or  less  simultaneously. 
The  growth  of  even  the  very  young  animal  is  not  simply  a 
production  of  protein  tissue,  but  normally  includes  more  or  less 
fat  production,  while  in  proportion  as  one  has  to  deal  with 
early  maturing  animals  it  is  desirable  to  begin  the  fattening 
proper  at  a  comparatively  early  stage  of  growth  (512). 

There  appears  to  be  no  reason  for  regarding  the  actual  fatten- 
ing process  as  being  essentially  different  in  the  growing  and 
in  the  mature  animal.  It  has  been  shown,  however  (453,  456) 
that  in  the  latter  case  no  material  excess  of  protein  over  that 
required  for  maintenance  is  necessary.  So  far  as  the  mere 
supply  of  building  materials  is  concerned,  therefore,  there  seems 
no  reason  to  suppose  that  the  actual  protein  requirement  for 
combined  growth  and  fattening  is  any  greater  than  that  for 
normal  growth  without  fattening.  The  conclusions  regarding 
the  protein  requirements  for  growth  recorded  in  Chapter  XI 
(482),  therefore,  may  be  regarded  as  applicable  also  to  young 
animals  that  are  being  fattened,  especially  since  they  were  de- 
rived in  part  from  results  on  immature  fattening  animals,  and 
from  this  point  of  view  the  increased  feed  supply  required  for 


MEAT  PRODUCTION  447 

the  fattening  might  consist  exclusively  of  non-nitrogenous 
nutrients. 

526.  Influence  on  digestibility.  —  In  the  actual  compound- 
ing of  rations  for  fattening,  however,  whether  for  mature  or  for 
growing  animals,  account  must  be  taken  of  the  fact  that  such 
a  considerable  addition  of  non-nitrogenous  nutrients  to  a 
maintenance  or  growth  ration  may  have  an  unfavorable  effect 
upon  its  digestibility.  In  particular,  it  has  been  shown  (723) 
that  a  large  proportion  of  easily  digestible  carbohydrates  in  a 
ration  (i.e.,  a  "  wide  "  nutritive  ratio)  tends  to  depress  the 
apparent  digestibility  of  the  protein.  Accordingly,  if,  starting 
with  a  ration  just  adequate  to  support  the  normal  rate  of  growth, 
the  attempt  be  made  to  convert  it  into  a  fattening  ration  by 
simply  increasing  its  digestible  carbohydrates,  the  effect  may  be 
to  virtually  diminish  the  amount  of  protein  available  so  that 
the  ration,  while  containing  abundant  material  for  fat  produc- 
tion, may  fail  to  supply  enough  protein  to  utilize  fully  the 
animal's  capacity  for  growth. 

The  increase  due  to  growth,  however,  is  an  important  factor 
of  the  cheaper  gains  made  by  immature  animals  (509).  In  in- 
creasing the  total  feed  supply  in  order  to  secure  the  fattening 
of  the  young  animal,  therefore,  it  is  important  to  avoid  the  dan- 
ger of  so  decreasing  the  apparent  digestibility  of  the  protein 
by  the  too  free  use  of  feeding  stuffs  rich  in  carbohydrates  as  to 
reduce  the  protein  supply  below  that  needed  for  growth.  More- 
over, it  has  been  found  (723-727)  that  a  relative  deficiency  of  ni- 
trogenous matter  in  a  ration  also  decreases  the  digestibility 
of  the  carbohydrates,  particularly  of  those  less  soluble  forms 
which  are  acted  upon  chiefly  by  the  fermentative  processes  in 
the  rumen  or  ccecum,  and  so  tends  to  reduce  the  energy  value 
of  the  ration. 

It  is  difficult,  however,  to  make  any  very  definite  statements 
regarding  the  practical  significance  of  these  effects  in  actual 
feeding.  Kellner  recommends  that  the  nutritive  ratio  (709)  of  a 
fattening  ration,  computed  in  the  usual  way,  be  not  made  wider 
than  about  1:8-9  f°r  cattle  and  sheep  and  1:10-12  for 
swine.  Ordinarily,  there  will  be  little  difficulty  in  compound- 
ing rations  conforming  to  this  rule,  especially  when  home  grown 
protein  feeds  are  available,  and  such  rations  when  fed  in  suf- 
ficient amounts  to  support  reasonably  rapid  fattening  would 


448  NUTRITION  OF  FARM   ANIMALS 

supply  more  digestible  protein  than  is  called  for  by  the  estimates 
in  Appendix  Table  IV  b.  When  protein  feeds  are  especially  ex- 
pensive an  even  smaller  proportion  of  protein  might  doubtless 
be  used  to  economic  advantage,  even  though  at  the  expense  of 
some  loss  of  digestibility,  without  unduly  curtailing  the  pro- 
tein supply,  especially  in  the  case  of  animals  approaching 
maturity. 

527.  Specific  effects  of  feeding  stuffs.  —  Account  must  be 
taken  also  of  the  fact  that  in  most  of  the  experiments  upon  the 
protein  requirement   thus  far  reported  the  variation  in   the 
protein  supply  was  effected  by  varying  the  proportions  of  cer- 
tain concentrates  in  the  ration,  such,  e.g.,  as  substituting  cotton- 
seed meal  for  maize.     As  was  suggested  in  Chapter  XI  (491), 
however,  such  a  substitution  may  not  only  affect  the  ash  bal- 
ance of  the  ration  but  may  serve  to  introduce  substances  which 
stimulate  the  growth  process  or  perhaps  the  fattening  process. 
While  we  are  not  to  suppose  that  such  substances  can  take 
the  place   of  actual  nutrients   (738),  they   might   enable   the 
protein  in  the  ration  to  be  more  fully  utilized,  or  they  might, 
by  stimulating  the  fattening  process,  create  an  appetite  for  more 
feed. 

At  any  rate  it  seems  to  be  the  general  experience  of  stockmen 
that  the  addition  of  certain  feeds  rich  in  protein,  especially  the 
oil  meals,  to  the  rations  of  fattening  animals  tends  to  induce 
them  to  consume  feed  more  freely  and  thus  (518)  to  yield  more 
profitable  gains. 

Energy  requirements  for  meat  production 

528.  Combined  growth  and  fattening.  —  An    attempt   was 
made  in  Chapter  XI  (480-483)  to  estimate  approximately  the 
net  energy  values  required  at  different  ages  for  normal  growth 
without  material  fattening.     To  the  extent  to  which  the  fatten- 
ing process  is  to  be  carried  on  at  the  same  time,  these  require- 
ments must  evidently  be  increased  by  amounts  equal  to  the 
additional  net  energy  stored  up  in  the  increase  of  adipose  tis- 
sue desired  or  expected.     Subject  to  the  limitations  indicated 
in  previous  paragraphs,  this  additional  energy  may  be  supplied 
by  the  addition  of  either  nitrogenous  or  non-nitrogenous  ma- 
terials to  the  growth  ration. 


MEAT  PRODUCTION  449 

It  was  estimated  in  Chapter  X  that  a  pound  of  increase  in 
live  weight  in  the  mature  fattening  animal  is  equivalent  to  about 
3.25  Therms  of  energy.  If  it  is  allowable  to  apply  this  average 
to  the  fattening  of  younger  animals,  this  would  be  equivalent 
to  saying  that  for  each  pound  of  increase  in  weight  above  that 
due  to  growth  proper,  about  3.25  Therms  of  net  energy  should 
be  added  to  the  requirements  for  growth  as  estimated  in  Chapter 
XI  (480-483).  The  energy  requirement  of  the  meat  animal, 
therefore,  will  obviously  depend  on  its  capacity  to  produce  gain 
of  flesh  or  fat  and  the  extent  to  which  it  is  desired  to  utilize  this 
capacity,  and  no  specific  and  invariable  requirements  can  be 
formulated. 

529.  Total  amount  of  feed.  —  If,  for  the  reasons  given  in 
previous  paragraphs,  the  proportion  of  digestible  protein  in  the 
ration  is  kept  above  a  certain  limit,  the  question  of  the  amount 
of  net  energy  to  be  supplied  resolves  itself  into  the  question  of 
the  most  profitable  total  amount  of  feed  to  be  given  and  this 
depends  upon  a  variety  of  conditions. 

It  has  already  been  pointed  out  (512)  that  only  with  animals 
having  a  rapid  rate  of  growth  and  maturing  early  is  it  advisable 
to  begin  intensive  feeding  before  a  fair  degree  of  maturity  is 
reached.  With  ordinary  animals  the  major  portion  of  their 
growth  may  be  more  cheaply  supported  upon  pasture  and  the 
ordinary  roughages  with  relatively  small  amounts  of  concen- 
trates, since  the  growth  process  cannot  be  materially  has- 
tened by  heavy  feeding.  When,  however,  the  time  for  begin- 
ning the  fattening  process  involving  the  use  of  expensive  con- 
centrates is  reached  (533),  whether  this  be  early  or  late,  it  is 
important  to  hasten  it  as  much  as  practicable  in  order  to  re- 
duce the  cost  of  maintenance,  attendance,  etc.,  and  the  question 
of  the  most  profitable  amount  of  feed  becomes  an  important  one. 

530.  Heavy  feeding  profitable.  —  That  comparatively  heavy 
feeding  of  fattening  animals  is  economically  advantageous  is 
shown  by  the  experience  of  practical  feeders,  and  is  evident  from 
the  fact,  to  which  attention  has  already  been  called  several  times, 
that  a  less  proportion  of  the  heavy  ration  is  required  for  the 
maintenance  of  the  animal.     Were  this  the  only  factor  involved, 
it  would  follow  mathematically  that  the  greater  the  amount  of 
feed  consumed  the  greater  would  be  the  growth  per  unit  of  feed 
and  therefore  that  the  appetite  of  the  fattening  animal  should 

2  G 


450  NUTRITION  OF  FARM  ANIMALS 

be  stimulated  to  the  greatest  extent  possible.      In  fact,  how- 
ever, other  considerations  come  in  to  modify  this  conclusion. 

531.  Influence   on   digestibility.  —  Overfeeding  to  the    ex- 
tent of  causing  digestive  disturbances  and  throwing  the  animal 
"  off  feed  "  is  of  course  to  be  avoided,  since  the  resulting  dis- 
turbance and   the  subsequent  lessened  consumption  of  feed 
may  outweigh  any  advantage  from  the  increased  amount  eaten. 
It  is  the  regular  uniform  feeder  that  is  likely  to  be  the  profitable 
animal  rather  than  the  one  with  a  capricious  appetite. 

But  aside  from  this  danger,  it  seems  well  established  that 
the  percentage  digestibility  of  mixed  rations,  such  as  would  be 
used  in  productive  feeding,  decreases  more  or  less  as  the  quantity 
consumed  increases.  The  results  on  record  in  this  respect  (722) 
are  scarcely  sufficient  for  any  quantitative  estimate  of  the  mag- 
nitude of  this  effect,  but  it  is  evident  that  it  must  tend  to  di- 
minish the  efficiency  of  the  rations. 

532.  Influence  on  net  energy  values.  —  Such  a  decrease  of 
digestibility  as  that  just  noted  is,  of  course,  equivalent  to  a 
decrease  in  the  net  energy  value  of  the  rations.     There  appears 
to  be  a  somewhat  general  impression,  however,  that  in  addition 
to  this  effect  on  digestibility,  the  matter  and  energy  actually 
resorbed  from  the  ration  become  less  efficient  in  producing 
gain  as  the  amount  of  the  ration  is  increased — in  other  words 
that  when  the  organism  is  flooded  with  the  resorbed  products 
of  digestion,  the  katabolic  processes  are  stimulated  and  a  larger 
share  of  the  energy  of  the  digested  matter  escapes  as  heat. 
As  appears  in  Chapter  XVII   (764),  the  evidence  on  this  point 
as  yet  seems  hardly  sufficient  to  warrant  positive  statements. 
The  net  energy  values  of  feeding  stuffs  which  have  thus  far  been 
reported  have  been  obtained  chiefly  in  experiments  on  rations 
ranging  from  submaintenance  to  only  moderately  heavy  fatten- 
ing rations,  and  the  results  show  no  distinct  indication  of  a 
decrease  with  increasing  amounts  of  feed.     On  the  other  hand, 
physiological  considerations  render  it  quite  conceivable  that 
the  effect  of  the  feed  in  stimulating  metabolism  and  so  increasing 
the  heat  production  (365)  may  be  relatively  greater  on  a  high 
than  on  a  low  nutritive  plane. 

Apparently  more  or  less  falling  off  in  the  nutritive  effect  of 
a  fattening  ration  as  its  amount  is  increased  must  be  antici- 
pated, whether  on  account  of  decreasing  digestibility  or  of 


MEAT  PRODUCTION  451 

lessened  utilization  of  the  digestible  matter  or  a  combination 
of  the  two.  Whether  this  diminution,  within  the  limits  of  the 
animal's  capacity  to  consume  feed,  is  sufficient  to  offset  the 
economic  advantage  of  such  increased  consumption  remains  to 
be  shown,  although  Morgen  1  reports  experiments  on  sheep  in 
which  very  heavy  rations  actually  produced  smaller  gains  in 
live  weight  than  lighter  ones.  Finally  it  should  be  remembered 
that  it  is  the  actual  gain  of  chemical  energy  by  the  animal  which 
is  believed  to  bear  a  tolerably  constant  relation  to  the  feed  en- 
ergy. It  has  been  repeatedly  pointed  out  that  the  gain  in  live 
weight  is  a  very  uncertain  indication  of  the  amount  of  energy 
stored  up.  It  is  quite  conceivable  that  the  larger  gain  to  be 
expected  on  the  heavier  ration  may  contain  less  water  and  more 
dry  matter  or  less  protein  and  more  fat  than  that  produced  on 
the  lighter  ration,  and  that  consequently  the  increase  in  weight 
may  not  be  proportional  to  the  increase  in  feed.  In  that  case, 
unless  the  higher  quality  of  the  gain  were  recognized  by  the 
market,  the  economic  advantage  attached  to  heavier  feeding 
would  be  diminished  or  wiped  out. 

533.  Proportion  of  concentrates  to  roughage.  —  The  fore- 
going considerations  apply  in   the  first  instance   to  varying 
amounts  of  the  same  mixture  of  feeding  stuffs.     In  the  case  of 
herbivora,  however,  heavy  feeding  must  necessarily  be  effected 
by  increasing  the  proportion  of  concentrates  or  of  roots  to 
roughage,  the  higher  cost  of  the  former  per  unit  of  net  energy 
being  more  than  offset  by  the  economic  advantage  incident  to 
the  much  larger  amount  which  can  be  consumed.     When  such 
an   addition  of  concentrates  contains  a  large  proportion  of 
carbohydrates  (as  in  the  case  of  maize  or  roots)  it  would  appear 
(724)  that  the  digestibility  of  the  rations  would  suffer  to  a  certain 
extent  owing  to  the  low  protein  content  of  the  ration,  while 
common  observation  indicates  a  more  rapid  passage  of  the 
feed  through  the  digestive  tract  of  heavily  grained  ruminants 
and  suggests  a  decrease  in  total  digestibility  which  has  not, 
however,  been  experimentally  confirmed. 

534.  Standards.  —  It  is  clear  from  the  foregoing  that  under 
ordinary  conditions  mature  or  nearly  mature  fattening  animals, 
such  as  the  cattle  ordinarily  fattened  in  the  United  States, 
should  be  fed  as  heavily  and  pushed  as  rapidly  as  the  capacity 

1  Futterung  und  Schlachtergebnisse,  pp.  22  and  33. 


452 


NUTRITION  OF  FARM  ANIMALS 


of  the  animals  and  the  skill  of  the  feeder  will  permit.  This 
conclusion  was  reached  long  ago  by  practical  feeders,  so  that  the 
results  of  experience  and  of  investigation  appear  quite  in  har- 
mony. Such  an  intensive  feeding  can  be  effected  only  by  a 
free  use  of  concentrates  and  unless  the  latter  are  very  expensive 
as  compared  with  roughages,  it  is  economy  to  use  them  to  the 
largest  practicable  extent. 

Under  these  conditions  it  is  evident  that  there  is  very  little 
significance  in  a  feeding  standard  in  the  ordinary  sense,  so  far 
at  least  as  the  amount  of  feed  is  concerned.  It  may,  it  is  true, 
afford  a  basis  for  preliminary  computation-  of  the  amount 
of  feed  required  for  a  season's  feeding,  if  this  is  of  any  impor- 
tance, but  in  actual  feeding  the  problem  is  to  induce  the  animals, 
by  means  of  the  art  of  the  skilled  feeder,  to  consume  large 
amounts  of  feed  without  injury  to  their  appetites  or  digestive 
capacity,  and  this  is  largely  a  question  of  the  individuality  of 
the  animal  or  lot.  The  one  thing  to  be  kept  in  mind  is  to  see 
that  the  supply  of  protein  in  the  ration  is  sufficient  to  ensure  the 
normal  growth  of  protein,  tissue,  since  this  causes  a  relatively 
rapid  increase  in  weight. 

For  younger  fattening  animals,  somewhat  more  definite  re- 
quirements might  be  formulated  in  the  manner  indicated  in  a 
previous  paragraph  (528)  on  the  basis  of  the  requirements  for 
fattening  and  for  growth  as  estimated  in  Chapters  X  and  XI. 

The  compilation  by  Bull  and  Emmett 1  of  American  experi- 
ments on  fattening  lambs  referred  to  in  Chapter  XI  (487)  in- 
cluded data  regarding  the  computed  net  energy  content  of  the 
rations.  They  conclude  that  the  production  of  satisfactory 
gains  required  the  following  amounts  of  digestible  protein  and 
net  energy  per  1000  pounds  live  weight. 

TABLE  117.  —  REQUIREMENTS  OF  FATTENING  LAMBS  PER  1000  LB.  LIVE 

WEIGHT 


LIVE  WEIGHT 

ESTIMATED  AGE 

DIGESTIBLE  PROTEIN 

NET  ENERGY 

Pounds 

Months 

Pounds 

Therms 

50-70 
70-90 

5 

7 

3-^-3-3 
2.5-2.8 

17-19 

18-20 

90-IIO 
IIO-I5O 

9 
15 

2.2-2.4 
1.4-1.9 

17-20 
16-19 

1  Ills.  Expt.  Sta.,  Bui.  166  (1914). 


MEAT  PRODUCTION  453 

No  similar  compilations  for  other  species  of  farm  animals  have 
yet  been  reported,  although  much  valuable  material  in  the 
publications  of  the  experiment  stations  awaits  such  discussion. 

§  4.  INFLUENCE  OF  EXTERNAL  CONDITIONS 

While  the  capacity  of  the  animal  as  a  meat  producer  and  a 
supply  of  feed  sufficient  in  quantity  and  quality  to  fully  utilize 
that  capacity  are  the  two  great  factors  in  meat  production,  yet 
the  conditions  under  which  the  animal  is  kept  are  not  without 
influence  on  the  results  obtained. 

Temperature 

535.  Teachings  of  practice.  —  Since  the  temperature  of  the 
animal  body  is  maintained  by  the  katabolism  of  materials  de- 
rived from  the  feed,  it  seemed  natural  to  conclude  that  cold 
surroundings  would  lead  to  a  wasteful  oxidation  of  feed  for 
simple  heat  production,  and  considerable  emphasis  has  been 
laid  in  the  past  upon  the  economic  importance  of  providing 
fairly  warm  quarters  for  live  stock.     At  the  same  time,  however, 
great  numbers  of  cattle,  in  particular,  were  being  successfully 
fattened  in  sheds  and  open  feed  lots  and  more  recently  a  con- 
siderable amount  of  experimental  work  has  been  reported  show- 
ing that  this  supposedly  uneconomic  practice  actually  gives 
better  returns  than  feeding  in  warm  quarters.     The  results  of 
a  considerable  number  of  such  comparisons  have  been  sum- 
marized by  the  writer  1  and  leave  no  doubt  as  to  the  validity 
of  this  conclusion,  while  it  is  entirely  in  harmony  with  the  prin- 
ciples governing  the  influence  of  external  temperature  upon 
metabolism  which  were  discussed  in  previous  chapters. 

536.  Critical  temperature.  —  As  was  shown  in  Chapter  VII 
(354),  there  is  a  certain  approximate  temperature,  called  the 
critical  temperature,  at  which  the  minimum  outflow  of  heat 
just  balances  the  necessary  heat  production  resulting  from  the 
internal  work  and  below  which  more  or  less  oxidation  of  tissue 
is  required  to  maintain  the  normal  temperature  of  the  body. 
Furthermore,  it  has  been  shown  (395-397)  that  the  digestion 
and  assimilation  of  feed  and  its  conversion  into  tissue  result  in 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  108  (1908),  pp.  7Q-86. 


454  NUTRITION  OF  FARM  ANIMALS 

the  evolution  of  relatively  large  amounts  of  heat,  especially 
in  the  ruminants,  and  that  the  effect  of  this  internal  produc- 
tion of  heat  is  virtually  to  lower  the  critical  temperature  as  com- 
pared with  that  of  the  fasting  animal.  In  other  words,  there  is 
for  each  animal  and  for  each  ration  a  certain  temperature  above 
which  the  heat  produced  becomes  in  part  an  excretum,  to  be 
gotten  rid  of  by  radiation  and  evaporation. 

It  appears  likely  that  a  certain  excess  of  heat  production  over 
that  absolutely  required  to  maintain  the  body  temperature  is 
advantageous,  both  as  promoting  the  comfort  of  the  animal  and 
especially  as  affording  a  margin  in  case  of  temporary  fluctuations 
of  temperature.  On  the  other  hand,  both  our  own  personal  sen- 
sations and  the  observations  of  practical  stock  feeders  show  that 
an  unnecessarily  high  temperature  is  debilitating,  affecting  both 
appetite  and  general  health.  In  practice,  then,  it  is  desirable  to 
keep  the  thermal  surroundings  of  the  animal  within  the  range 
above  indicated  —  somewhat  above  the  critical  point  but  not 
so  much  so  as  to  affect  the  appetite  and  thrift.  It  is  evident 
that  the  limits  of  this  range  may  vary  widely  with  the  kind  of 
animal  and  with  the  amount  of  the  ration. 

537.  Amount  of  ration.  —  The  influence  of  this  factor  upon 
the  requirements  for  protection  from  cold  is  clearly  indicated 
by  what  has  already  been  said.     The  heavier  the  ration,  other 
things  being  equal,  the  more  heat  will  be  evolved  during  its 
digestion  and  conversion  into  tissue.     Mature  animals  on  full 
feed  thus  have  at  their  disposal  a  large  amount  of  surplus  heat 
and  naturally  can  thrive  under  conditions  of  exposure  which 
might  be  seriously  detrimental  to  young,  growing  animals  on 
relatively  light  rations.     Thus  one  of  Kellner's  experiments  on 
a  fattening  ox  gave  the  following  results :  — 

TABLE  118.  —  EXCESS  HEAT  PRODUCTION  IN  FATTENING 

Metabolizable  energy  of  ration 26,600  Cals. 

Energy  stored  as  gain 5>92°  Cals. 

Energy  evolved  as  heat 20,740  Cals. 

Computed  maintenance  requirement    ....  15,060  Cals. 

Excess  of  heat 5, 680  Cals. 

Excess  over  maintenance 37-7% 

538.  Age  and  weight  of  animals.  —  The  internal  work  of 
like  animals  of  different  sizes,  under  like  conditions,  appears  to 


MEAT  PRODUCTION  455 

be  approximately  proportional  to  their  body  surface  (345), 
and  there  is  even  good  ground  for  believing  that  this  law  applies 
in  a  broad  way  to  animals  of  the  most  diverse  species  and  size. 
Since  the  action  of  external  temperature  is  also  approximately 
proportional  to  the  surface,  it  would  be  expected  that  the  size 
of  the  animal  would  not  be  an  important  factor.  In  fact,  however, 
the  other  conditions  are  rarely  alike.  The  young  animal  in 
particular  is  likely  to  be  getting  a  relatively  lighter  ration  than 
the  animal  which  is  being  pushed  for  the  butcher,  and  thus  to 
have  less  surplus  heat  at  its  disposal,  while  the  indefinable  factor 
of  "  hardiness  "  would  also  seem  to  be  in  favor  of  the  older 
animal. 

539.  Humidity.  —  The  relative  humidity  of  the  air  is  an  im- 
portant factor  in   the   temperature  relations   of   the  animal. 
Moist  air  tends  to  increase  the  conductivity  of  the  hair  or  wool, 
just  as  it  does  that  of  the  clothing  of  man,  thus  facilitating  the 
escape  of  heat  and  raising  the  critical  temperature.     Accord- 
ingly, it  is  to  be  anticipated  that  in  a  dry  climate,  like  that  of 
the  northwestern  United  States,  animals  might  be  safely  exposed 
to  a  greater  degree  of  cold  than  in  a  damp  climate,  like  the 
winter  of  the  seaboard  States. 

540.  Temperature    of    drinking    water.  —  In    general,    the 
same  considerations  adduced  in  discussing  the  influence  of  the 
temperature  of  the  air  apply  to  that  of  the  drinking  water. 
Under  heavy  feeding,  especially,  unless  in  very  cold  quarters, 
the  animal  has  a  surplus  of  heat  which  it  can  apply  to  warming 
its  drink.     If,  then,  the  latter  is  at  such  a  temperature  as  to  be 
consumed  freely,  there  would  seem  to  be  no  occasion  for  heating 
it  further,  except  for  one  important  consideration.     The  tem- 
perature of  the  air  acts  continuously  and  with  approximate 
uniformity.     That  of  the  water,  on  the  other  hand,  acts  only 
at  intervals,  often  only  two  or  three  times  or  even  once  per  day. 
If,  now,  the  animal  consumes  within  a  short  time  a  large  amount 
of  cold  water,  a  correspondingly  rapid  expenditure  of  heat  is 
required  to  warm  this  water  to  the  body  temperature,  and  this 
demand  may  for  a  time  exceed  the  supply  of  surplus  heat  and 
cause  an  increased  oxidation  of  tissue  or  food  material  for  the 
sake  of  heat  production  only.     Such  a  loss  can  never  be  made 
good  at  a  later  hour  since,  once  converted  into  heat,  the  energy 
has  escaped  from  the  grasp  of  the  body.    Other  things  being 


NUTRITION  OF  FARM  ANIMALS 

equal,  then,  it  will  clearly  be  desirable  to  have  the  water  con- 
sumption approximate  as  nearly  as  possible  a  continuous  con- 
sumption by  having  it  constantly  accessible,  while  if  the  stock 
are  watered  only  at  intervals  the  temperature  of  the  water  may 
need  to  be  rather  higher  than  in  the  other  case. 

Shelter 

A  protection  from  rain  or  snow  and  from  wind  may  be  of  quite 
as  much  importance  as  protection  from  low  temperatures  simply. 

541.  Precipitation.  —  An   important   factor   in   the  case  is 
the  amount  of  precipitation  (rain  or  snow)  to  be  expected  dur- 
ing the  feeding  period.     In  cold  weather  the  low  temperature 
of  the  water  which  penetrates  to  the  skin  of  animals  is  the  cause 
of  a  loss  of  heat  which  may  be  regarded  as  practically  an  ad- 
dition to  that  due  to  the  cold  air,  the  extent  of  both  losses  being 
affected  by  the  thickness  of  the  animal's  coat.     Far  more  im- 
portant   than    this,  however,  is  the  expenditure  of   heat   re- 
quired to  dry  out  the  coat  after  it  is  wet,  and  this,  as  it  would 
seem  and  as  some  of  the  experiments  with  sheep  seem  to  indi- 
cate, would  be  greater  with  the  heavier  coated  animal  when  it 
has  once  become  thoroughly   wet.     Still   greater,  relatively,  is 
the  heat  required  to  melt  the  snow  falling  on  the  animal  or  that 
upon  which  it  is  compelled  to  lie. 

These  effects,  it  will  be  observed,  are  largely  independent  of 
the  indications  of  the  thermometer,  and  it  is  clear  that  the 
nature  of  the  climate  as  regards  humidity  and  precipitation  is 
quite  as  important  a  factor  as  the  temperature  in  its  bearing 
on  the  question  of  shelter,  and  that  in  many  localities  a  roof  to 
shelter  the  animals  from  storms  may  be  as  efficient  as  a  tight 
barn.  One  advantage  of  the  roof,  already  mentioned  inci- 
dentally, is  that  it  provides  the  possibility  of  a  dry  bed,  thus 
not  only  adding  to  the  comfort  of  the  stock  but  avoiding  ex- 
penditure of  energy  in  warming  up  or  evaporating  water  or  melt- 
ing snow  or  ice. 

542.  Wind.  —  All  are  familiar  with  the  greater  severity  of  a 
windy  day  as  compared  with  a  still  one  of  the  same  temperature. 
A  large  part  of  the  protective  value  of  the  clothing  of  man  or 
the  coat  of  an  animal  resides  in  the  air  entangled  between  the 
fibers  of  the  material.    Wind  tends  to  replace  this  air  with  fresh, 


MEAT  PRODUCTION  457 

cold  air  and  thus  greatly  reduces  the  protective  effect.  A  wind- 
break, therefore,  may  have  a  distinct  economic  value  in  stock 
feeding. 

543.  Insolation.  —  The  effects  of  the  weather  are  appreciably 
modified  by  the  exposure  of  stock  to  direct  sunlight.     Aside  from 
any  direct  effect  of  the  light  as  such,  a  not  inconsiderable  amount 
of  heat  is  imparted  to  the  body  by  the  sun's  rays.     During  cold 
weather  this  is  likely  to  be  a  distinct  advantage,  but  during  the 
hot  months  the  reverse  is  true.     Since  the  animal  cannot  re- 
duce its  heat  production  below  that  resulting  from  its  internal 
work  and  the  digestion  and  assimilation  of  its  feed,  it  may  se- 
riously tax  its  powers  to  dispose  of  the  additional  heat  imparted 
by  the  direct  sunlight.     In  this  case  shelter  of  some  sort  may 
be  required  for  opposite  reasons  to  those  obtaining  during  the 
cold  months.    .For  similar  reasons  a  supply  of  cool,  fresh  water 
and  exposure  to  the  wind  may  be  of  great  advantage  in  helping 
the  animal  to  get  rid  of  its  surplus  heat. 

Other  conditions 

544.  Exercise.  —  The  well-known  fact  that  muscular  exer- 
tion is  accomplished  at  the  expense  of  the  katabolism  of  tissue 
and  ultimately,  therefore,  at  the  expense  of  the  feed,  would  seem 
at  first  thought  to  indicate  that  the  activity  of  the  meat-produc- 
ing animal  should  be  restricted  as  much  as  practicable.     In  the 
case  of  the  growing  animal,  however,  another  very  important 
element  enters  into  the  case,  namely,  the  fact  that  moderate 
exercise  tends  to  stimulate  the  growth  of  the  muscular  system, 
or,  in  other  words,  the  production  of  lean  meat.     Since  this  is 
the  essential  object  sought,  a  normal  and  reasonable  amount  of 
muscular  activity  on  the  part  of  the  growing  animal  should  be 
allowed  and  encouraged,  even  though  the  muscular  exercise 
involves  the  consumption  of  more  feed.     Accordingly,  young 
stock  should  be  given  the  freedom  of  the  pasture  or  range  to 
as  great  an  extent  as  practicable,  while  at  the  same  tune  care 
should  be  taken  to  supply  abundant  feed  containing  a  sufficient 
supply  of  protein  in  order  that  enough  material  may  be  present 
to  supply  the  demand  for  growth  stimulated  by  the  exercise. 

In  the  case  of  breeding  stock,  especially,  a  most  important 
consideration  is  that  of  the  health  and  stamina  of  the  animal, 


458  NUTRITION  OF  FARM  ANIMALS 

which  can  hardly  fail  to  suffer  through  overconfinement.  The 
above  principles  apply  in  a  general  way  to  all  classes  of  stock. 
In  particular,  hogs  should  be  given  an  opportunity  for  more 
movement  and  exercise  than  is  frequently  allowed. 

In  the  case  of  animals  which  have  reached  the  fattening  stage, 
on  the  other  hand,  there  is  comparatively  little  growth  of  pro- 
tein tissue,  while  it  is  only  necessary  to  maintain  sufficient  health 
to  ensure  a  normal  appetite  and  assimilation  of  feed.  In  pro- 
portion, then,  as  this  stage  is  reached,  the  endeavor  should  be 
to  reduce  the  amount  of  exercise  taken  and  to  keep  the  fatten- 
ing animal  as  quiet  as  possible.  To  this  end  comfortable  quar- 
ters should  be  provided,  with  plentiful  bedding,  and  the  animals 
should  be  kept  -as  undisturbed  as  possible,  so  that  they  may 
"  eat  and  lie  down."  This  is  particularly  important  in  the  case 
of  the  sheep  on  account  of  its  timid  nature.  For  similar  rea- 
sons it  is  desirable  to  have  the  water  supply  of  fattening  animals 
close  at  hand. 

545.  Water  supply.  —  It  should  never  be  forgotten  that 
rapid  production,  involving  the  utilization  of  relatively  large 
amounts  of  feed,  requires  the  consumption  of  a  corresponding 
amount  of  water  for  the  physiological  purposes  of  the  animal. 
For  this  reason,  as  well  as  for  the  one  previously  mentioned  (540), 
it  is  desirable  that  stock  should  have  ready  access  to  water,  if 
possible,  at  all  times  and  that  the  water  supplied  should  not  be 
too  cold  to  be  consumed  freely  by  the  animals. 


CHAPTER  XIII 

MILK    PRODUCTION 

§  i.   THE  PHYSIOLOGY  OF  MILK  PRODUCTION 

546.  Components  of  milk.  —  In  addition  to  water,  milk 
contains  representatives  of  the  four  great  groups  of  nutrients, 
viz.,  proteins,  fats,  carbohydrates  and  ash. 

Proteins.  —  The  principal  protein  of  milk  is  casein,  a  sub- 
stance belonging  to  the  group  of  phosphoproteins  (65).  This 
protein  is  peculiar  to  milk,  not  being  found  elsewhere  in  the 
body. 

In  addition  to  casein,  milk  contains  also  a  lact-albumin  and  a 
paraglobulin  in  small  amounts.  Their  presence  may  be  demon- 
strated by  precipitating  the  casein  by  means  of  acid  and  heating 
the  nitrate.  Traces  of  peptones,  possibly  due  to  the  presence 
of  a  proteolytic  enzym,  are  also  found  in  milk. 

According  to  Konig,  the  casein  content  of  milk  has  been 
observed  to  vary  from  1.79  per  cent  to  4.23  per  cent  and  that 
of  the  other  proteins  from  0.25  per  cent  to  1.44  per  cent. 

Fats.  —  Fats  occur  in  milk  in  the  form  of  microscopic  glob- 
ules varying  greatly  in  size  and  held  in  suspension  in  the  col- 
loidal solution  of  casein.  In  cow's  milk  the  diameter  of  these 
fat  globules  may  be  stated  in  a  general  way  to  range  from 
0.0016  to  o.oi  millimeter  and  in  a  single  cubic  centimeter  of 
average  milk  their  number  runs  into  the  millions.  The  fat 
globules  were  formerly  described  as  surrounded  by  a  membrane 
of  a  protein  nature,  but  the  supposed  membrane  is  now  re- 
garded as  simply  a  condensation  of  the  protein  of  the  milk,  due 
to  surface  tension. 

Milk  fat,  like  other  animal  fats,  is  a  mixture  of  a  number  of 
simple  fats  or  triglycerids.  As  compared  with  body  fats,  the 
fat  of  milk  is  relatively  rich  in  olein  and  consequently  has  a 
relatively  low  melting  point.  It  is  especially  distinguished  from 

459 


460  NUTRITION  OF  FARM  ANIMALS 

body  fat,  however,  by  the  presence  of  a  considerable  proportion 
of  fatty  acids  of  low  molecular  weight,  as  already  noted  in 
Chapter  I  (30),  where  a  list  of  the  principal  constituents  is 
given.  The  presence  of  these  so-called  "  volatile  fatty  acids  " 
(i.e.,  acids  which  can  be  distilled  in  a  current  of  steam)  affords 
an  important  means  for  the  detection  of  adulterations  of 
butter. 

The  percentage  of  fat  in  milk  varies  widely.  For  the  cow  a 
minimum  of  1.67  per  cent  is  reported  by  Konig.  Six  per  cent, 
on  the  other  hand,  is  a  high  figure,  although  occasionally  7  per 
cent  is  reached.  Babcock  states  that  9  per  cent  is  the  maxi- 
mum observed  for  a  cow  giving  as  much  as  15  pounds  of  milk 
daily. 

The  milk  fat  carries  traces  of  lecithins  and  cholesterins 
and  also  varying  amounts  of  coloring  matter,  derived,  as 
Palmer  and  Eckles  1  have  shown,  chiefly  from  the  carotin  of 
the  feed. 

Carbohydrates.  —  Milk  contains  in  solution  a  disaccharid 
peculiar  to  itself,  namely,  lactose,  or  milk  sugar  (13).  In 
distinction  from  fat,  the  percentage  of  lactose  in  fresh  milk 
shows  comparatively  small  variations,  averaging  about  5  per 
cent  in  cow's  milk.  The  souring  of  milk  is  brought  about  by  a 
fermentation  of  the  milk  sugar  by  which  its  molecule  is  split 
into  four  molecules  of  lactic  acid. 

Among  the  organic  ingredients  of  milk  should  also  be  men- 
tioned citric  acid,  which  occurs  in  appreciable  quantities  in  the 
form  of  calcium  citrate. 

Ash.  —  The  total  mineral  matter  in  cow's  milk  averages 
about  0.7  per  cent  according  to  Van  Slyke.2 

Qualitatively,  the  ash  of  milk  contains  the  same  ingredients  found 
in  all  animal  substances.  Its  quantitative  composition,  however,  as 
compared  with  the  blood  serum,  on  the  one  hand,  and  with  that  of 
the  tissues  on  the  other,  shows  some  interesting  relations.  Bunge  3 
gives  the  following  figures  for  the  composition  of  the  ash  of  the  serum 
of  cattle  blood  and  of  the  ash  of  cow's  milk.  To  these  have  been 
added  Lawes  and  Gilbert's  figures  for  the  ash  of  a  calf  for  the  sake 
of  comparison. 

1  Jour.  Biol.  Chem.,  17  (1914),  191-264. 

2  Jordan,  The  Feeding  of  Animals,  1908,  p.  305. 
sZtschr.  Biol.,  10  (1874),  301 ;  12  (1876),  191. 


MILK  PRODUCTION 

TABLE  1 19.  —  PERCENTAGE  COMPOSITION  OF  ASH 


461 


SERUM  or 
CATTLE 
BLOOD 

Cow's 
MILK 

BODY   OF 

CALF 

K2O 

% 

32 

% 
22  I 

% 

Na2O         

C  C  I 

I  3  O 

*  82 

CaO      

I  6 

2O  O 

A-3  nr 

MgO 

06 

2  6 

Fe2O3    .... 

O  I 

O  Od. 

o  r  2 

Cl     

4.7  i 

212 

O  1  2 

P2O5 

•3     A 

24  8 

With  smaller  animals,  having  a  shorter  period  of  growth,  the  rela- 
tions are  even  more  striking.  Thus,  for  the  rabbit  Bunge  l  reports 
the  following  results. 

TABLE  1 20.  —  PERCENTAGE  COMPOSITION  OF  ASH 


SERUM  OF 
RABBIT 
BLOOD 

RABBIT 
MILK 

BODY  OF 
14  DAYS 
OLD 
RABBIT 

K2O 

•2    2 

IO  I 

IO  8 

Na2O              

^4.  7 

7  Q 

6  o 

CaO 

I  A 

•2  C    7 

•7  C   O 

MeO 

o  6 

2  2 

2  2 

Fe2O3    

O  O 

O  I 

O  2 

Cl     

4.7.8 

r  4 

4.Q 

P2O5 

2  o 

•2Q   Q 

4.1  Q 

It  appears  that  while  sodium  and  chlorin  are  the  predominant 
ingredients  of  the  blood  serum,  these  elements  are  present  in  milk  in 
relatively  small  proportions,  while  potassium,  calcium  and  phos- 
phorus predominate  in  the  latter,  the  ash  of  milk  closely  resembling 
that  of  the  body  of  the  same  species. 

647.  Average  composition.  —  Wing 2  cites  the  following 
figures  as  showing  approximately  the  average  composition  of 
cow's  milk 3  according  to  various  authorities. 

1  Quoted  by  Sellheim  in  Nagel's  Handbuch  fiir  Physiologic,  II,  188. 
3  Milk  and  its  Products,  1897,  p.  17. 

3  For  data  regarding  the  composition  of  the  milk  of  other  species  than  cattle, 
see  Schaefer's  Text  Book  of  Physiology,  Vol.  I,  p.  125. 


462  NUTRITION  OF   FARM   ANIMALS 

TABLE  121.  —  AVERAGE   COMPOSITION  OF  Cow's  MILK 


AMERICAN 
(Babcock) 

ENGLISH 
(Oliver) 

GERMAN 
(Fleisch- 
mann) 

FRENCH 
(Cornevin) 

Water  
Fat  
Casein 

87.17 

3-69 
302 

87.60 

3-25 

•2    AQ 

87.75 
3-40 
2  80 

87-75 
3-30 

Albumin  
Sugar  
Ash 

0-53 
4.88 
O  71 

°-45 
4-55 

O   7C 

0.70 
4.60 
O  7  C 

4.80 

O  7  e 

IOO.OO 

IOO.OO 

IOO.OO 

99.60 

548.  Milk  glands.  —  The  milk  glands,  properly  speaking, 
are  two  in  number,  one  on  each  side  of  the  median  line  of  the 
body,  although  in  many  animals  each  gland  is  subdivided  into 
two  or  more  lobes  having  separate  outlets 
or  teats.  Thus  in  the  horse  and  sheep 
each  gland  has  two  lobes,  in  the  cow 
two  or  three,  and  in  the  hog  from  ten  to 
fourteen.  The  milk  gland  is  classified 
as  a  compound  tubulo-acinous  gland.  Its 
structure  may  be  roughly  compared  to 
that  of  a  bunch  of  grapes.  It  consists 
of  a  great  number  of  acini  or  alveoli, 
three  of  which  are  shown  schematically 
FIG.  40.— Lobule  of  milk  in  Fig.  40,  corresponding  to  the  single 
berries  of  the  grape  cluster.  Each  alve- 
olus  consists  of  an  outer  layer  of  con- 
nective tissue  carrying  capillary  blood  vessels,  nerves  and 
lymphatics.  These  alveoli  are  about  ^  of  an  inch  in  diameter 
and  are  united  in  groups  of  3  to  5  to  form  lobules  having 
a  common  outlet  as  shown  in  the  figure.  Internally,  the 
alveoli  are  lined  with  a  single  layer  of  epithelial  cells  (Fig.  41), 
which  are  the  active  agents  in  secreting  milk.  The  ducts  or 
passages  leading  from  the  alveoli  are  also  lined  with  epithelial 
cells  but  of  a  different  sort  and  which  do  not  produce  milk. 
These  ducts  unite  to  form  larger  ones,  as  shown  in  Fig.  42,  which 
lead  finally  to  the  teat,  emptying  first  into  the  so-called  "  milk 
cistern,"  a  cavity  lying  near  the  base  of  the  teat.  In  compound 


MILK  PRODUCTION 


463 


milk  glands  there  is  more  or  less  connection  through  these 
milk  ducts  between  the  several  lobes,  but  none  between  the 
two  glands  on  either  side  of  the  body. 
The  milk  gland,  therefore,  consists 
of  a  framework  of  connective  tissue 
carrying  more  or  less  fat,  of  alveoli, 
milk  ducts,  veins,  arteries,  lymph  vessels 
and  nerves,  the  whole  forming  a  reddish 
gray  spongy  mass.  In  the  cow  the  -y 
two  glands  constituting  the  udder  are 
separated  by  a  band  of  fibrous  tissue 
which  serves  to  support  the  organ. 
The  udder  may  vary  widely  in  the 
proportion  of  connective  and  fatty 
tissue  on  the  one  hand  and  of  true 

,   .         ,.N  ,  FIG.  41.  —  Alveoli  of  milk 

secreting  tissue  (alveoli)  on  the  other.  gland.    (wikkens,  Form  und 

A  large  proportion  of  the  former  gives    Leben   der   Landwirthschaft- 

what  is  commonly  known  as  a  fleshy  Uchen  Hausthiere-) 
udder.     The  size  of  the  udder,  therefore,  is  not  the  sole  criterion 

of  its  capacity  as  a  milk  pro- 
ducing organ. 

At  the  branches  of  the  milk 
ducts  are  located  sphincter 
muscles  which  are  more  or  less 
under  the  control  of  the  animal 
and  the  contraction  of  which 
interferes  with  the  flow  of 
milk,  enabling  the  animal,  as 
the  phrase  goes,  to  "  hold  up  " 
her  milk. 

549.  Development  of  milk 
glands.  —  In  the  young  animal, 
the  milk  glands  are  rudimen- 
tary and  in  the  male  remain  so 
during  life,  except  in  extraor- 
dinary cases.  In  the  female, 
however,  as  sexual  maturity 
approaches,  a  considerable 
formation  of  glandular  tissue 

wirthschaftlichen  Hausthiere.)  takes    place,    but     the    glands 


464  NUTRITION  OF  FARM  ANIMALS 

reach  their  full  development  only  in  the  later  stages  of  preg- 
nancy. At  that  time,  a  rapid  growth  of  the  alveoli  and  per- 
haps the  formation  of  new  ones  occurs,  the  stimulus  to  this 
growth  being,  according  to  Bayliss  and  Starling,  the  formation 
of  certain  stimulating  substances  (Hormones)  in  the  fetus  which 
.pass  into  the  blood  of  the  mother  and  so  reach  the  milk  glands. 
That  other  causes  may  at  least  cooperate,  however,  is  shown 
by  the  apparently  well-established  fact  that  the  regular  re- 
moval of  the  fluid  found  in  the  glands  of  the  virgin  animal, 
or  even  mechanical  stimulation,  may  lead  to  the  formation 
of  considerable  quantities  of  milk,  in  some  instances  even  in 
the  male. 

550.  The  secretion  of  milk.  —  That  milk  formation  is  a  true 
secretion  and  not  a  mere  nitration  of  material  from  the  blood 
is  clearly  shown  by  the  facts  already  stated  regarding  the  com- 
position of  milk.  As  was  pointed  out,  all  the  principal  organic 
ingredients  of  the  milk  are  peculiar  to  it.  Casein  and  lactose 
are  not  found  elsewhere  in  the  animal  body,  and  while  the  prin- 
cipal simple  fats  of  milk  are  also  found  in  the  body  fat,  their 
proportions  are  different  in  the  milk  fat  and  the  latter  is  specially 
characterized  by  the  presence  of  glycerids  of  the  lower  acids 
of  the  aliphatic  series.  Furthermore,  even  more  marked  quan- 
titative differences  exist  between  the  mineral  elements  of  the 
milk  and  those  of  the  blood  serum.  From  all  these  facts,  it  is 
clear  that  the  milk  gland  is  a  producing  or  secreting  organ  and 
that  the  solid  ingredients  of  the  milk  are  largely  manufactured 
in  it  out  of  materials  derived  from  the  blood. 

A  theory  of  milk  secretion  first  propounded  by  Virchow 
found  wide  acceptance.  According  to  this  theory,  milk  pro- 
duction consists  essentially  of  a  physiological  fatty  degeneration 
of  the  epithelial  cells  of  the  alveoli.  The  microscope  shows  that 
the  cells  of  the  actively  secreting  gland  are  larger  than  those 
in  the  resting  gland  and  more  or  less  filled  with  fat  globules, 
especially  on  the  side  toward  the  cavity  of  the  alveolus.  It  was 
held  that  while  this  process  went  on  the  cell  divided,  forming 
two  or  more,  and  that  finally  the  cell  next  to  the  cavity  liquefied, 
setting  free  the  fat  globules  which  it  contained'  and,  perhaps 
with  the  addition  of  more  or  less  water,  constituted  the  milk. 
Milk  production  was  thus  regarded  as  a  form  of  the  growth  of 
tissue. 


MILK  PRODUCTION  465 

Subsequent  investigation,  however,  has  generally  failed  to 
show  satisfactory  evidence  of  cell  division.  A  modification 
of  Virchow's  theory  still  held  is  that  while  there  is  no  cell  division, 
the  outer  portion  of  the  protoplasm  is  sloughed  off  and  dissolved, 
forming  the  milk,  and  is  again  renewed  by  the  growth  of  new 
protoplasm.  The  weight  of  opinion,  however,  regards  milk 
production  as  a  true  secretion,  entirely  analogous  to  that  ob- 
served in  other  glands.  It  is  not  believed  that  there  is  normally 
a  breaking  down  of  cells,  but  that  the  latter  extrude  their 
secreted  materials  into  the  alveolus  precisely  as  do  the  secreting 
cells  of  other  glands.  This  is  held  to  apply  to  the  fat  globules 
as  well  as  to  the  other  ingredients  of  milk.  The  process  is  in 
many  ways  analogous  to  that  of  the  resorption  of  digested 
material  by  the  epithelial  cells  of  the  small  intestine,  the  obvious 
difference  being  the  direction  in  which  the  materials  move. 

The  secretion  of  milk  in  the  active  udder  is  a  more  or  less 
continuous  process,  the  product  accumulating  in  the  cavities 
and  passages  of  the  gland.  Fleischmann  long  ago  showed, 
however,  that  the  cavities  of  the  udder  cannot  possibly  contain 
the  amount  of  milk  produced  in  a  single  milking  by  a  reason- 
ably productive  cow,  and  it  is  well  recognized  that  a  rapid  secre- 
tion of  milk  occurs  during  suckling  or  milking.  In  other  words, 
the  milk  gland,  like  other  glands,  reacts  to  a  specific  stimulus. 

551.  Sources  of  ingredients  of  milk.  —  While  the  ultimate 
source  of  the  material  contained  in  the  milk  is  of  course  the 
feed,  the  milk  gland  draws  its  supply  of  material  for  milk  pro- 
duction immediately  from  the  blood,  while  at  the  same  time  it 
brings  about  extensive  chemical  transformations  in  the  sub- 
stances thus  supplied.     Probably  all  the  ingredients  of  the 
milk  should  be  regarded  as  products  of  the  chemical  activity 
of  the  epithelial  cells  of  the  glands,  although  the  extent  to  which 
the  original  material  is  modified  varies. 

552.  Origin  of  milk  proteins.  —  The  albumin  and  globulin 
of  milk  are  quite  similar  to  the  corresponding  substances  in  the 
blood.    The  casein,  on  the  other  hand,  is  radically  different. 
In  the  first  place,  it  is,  as  already  stated,  a  conjugated  protein 
containing    some    phosphorus-bearing    radicle.      Whether    the 
latter  is  derived  exclusively  from  the  organic  phosphorus  com- 
pounds of  the  feed  has  not  been  demonstrated,  although  it 
appears  probable  that  inorganic  phosphorus  compounds  (phos- 

2  H 


466 


NUTRITION  OF   FARM   ANIMALS 


phates)  may  be  utilized  as  sources  of  the  phosphorus  of  the  milk 
(257,  258,  497). 

The  production  of  casein,  however,  is  not  simply  ,a  conju- 
gation of  a  simple  protein  with  a  phosphorus  group.  The 
constitution  of  casein  is  markedly  different  from  that  of  the 
proteins  of  the  blood  serum  or  of  the  muscles,  as  is  shown  by 
the  proportions  of  its  various  cleavage  products  as  given  in 
Chapter  I  (50),  so  that  if  casein  is  formed  from  the  protein  of  the 
blood  or  tissue,  a  considerable  reconstruction  of  their  mole- 
cules is  necessary.  On  the  other  hand,  if  the  casein  of  the  milk 
is  built  up  in  the  epithelial  cells  of  the  udder,  in  the  manner 
suggested  in  Chapter  V  (226,  227),  from  the  simpler  cleavage 
products  in  the  blood,  the  process  is  specific  for  the  milk  gland. 

553.  Origin  of  milk  fats.  —  It  was  stated  in  Chapter  V  (247- 
249)  in  discussing  the  sources  of  body  fat  that  although  the  latter 
may  be  derived  in  part  from  the  fat  of  the  feed  and  show  some 
of  its  characteristics,  nevertheless,  the  production  of  fat  must 
be  regarded  as  due  essentially  to  the  activity  of  the  fat  cells, 
and  not  to  a  simple  deposition. 

In  the  first  place,  it  has  been  demonstrated  by  the  researches 
of  Jordan  and  others  that  milk  fat  as  well  as  body  fat  may  be 
formed  from  the  carbohydrates  of  the  feed. 

In  Jordan's  l  experiments  cows  were  fed  either  with  an  ordinary 
ration  or  with  one  very  poor  in  fat  and  the  production  of  fat  in  the 
milk  determined.  After  deducting  the  maximum  amounts  of  fat 
which  could  possibly  be  accounted  for  by  the  protein  and  fat  of  the 
feed,  a  considerable  balance  was  left  which  could  only  have  been  pro- 
duced from  the  carbohydrates.  The  following  table  gives  a  summary 
of  the  results :  — 

TABLE  122.  —  PRODUCTION  OF  FAT  BY  Cows 


NUMBER 
or  DAYS 

TOTAL  PRO- 
TEIN 2  METAB- 
OLISM 

EQUIVALENT 
FAT 

FAT  OF 
FEED 

TOTAL  FROM 
FAT  AND 
PROTEINS 

FAT  ACTUALLY 
PRODUCED 

Grams 

Grams 

Grams 

Grams 

Grams 

59 

15,109 

7,766 

1,490 

9,256 

17,585 

74 

34,661 

17,816 

2,211 

20,027 

37,637 

4 

2,209 

1,131 

1,504 

2,635 

3,289 

1  N.  Y.  (Geneva)  Expt.  Sta.,  Buls.  132  and  197. 

2  Digested  protein  of  feed  less  gain  of  protein  by  the  animal. 


MILK  PRODUCTION  467 

It  should  perhaps  be  pointed  out  that  the  formation  of  fat  from 
carbohydrates  in  these  experiments  may  not  necessarily  have  occurred 
in  the  milk  gland  itself.  It  is  entirely  conceivable  that  the  main 
portion  of  the  synthesis  of  the  fat  may  have  taken  place  elsewhere 
and  that  the  fat  or  its  precursors  were  simply  transferred  to  the  milk 
gland. 

Second,  it  has  also  been  shown  by  a  considerable  number  of 
experiments  that,  as  in  the  case  of  body  fat,  the  fat  of  the  feed 
may  sensibly  affect  the  properties  of  the  milk  fat.  Not  only 
have  changes  in  the  melting  point,  iodin  number,  and  other 
properties  of  butter  fat  been  found  to  follow  in  a  general  way 
similar  changes  in  the  feed  fat,  but  characteristic  ingredients 
of  foreign  fats  given  in  the  feed  have  been  detected  in  the  milk. 
While  it  is  not  necessary  to  conclude,  and  is  indeed  unlikely, 
that  the  feed  fat  is  simply  transferred,  as  it  were  mechanically, 
to  the  milk,  it  is  clear,  on  the  other  hand,  that  relatively  large 
fragments  of  the  fat  molecule  are  able  to  pass  through  the 
epithelial  cells  into  the  milk.  These  facts  render  it  evident 
that  feed  fat  is  a  source  of  milk  fat.  Not  only  so,  but  experi- 
ments by  Morgen  and  his  associates,  to  be  mentioned  later  (613), 
seem  to  show  that  a  certain  amount  of  fat  in  the  feed  (in  her- 
bivorous animals  at  least)  conduces  to  the  most  efficient  pro- 
duction of  milk  fat. 

The  idea  that  the  fat  of  milk  is  produced  synthetically  to  a 
considerable  extent  is  perhaps  supported  also  by  the  presence 
in  it  of  the  lower  acids  of  the  aliphatic  series,  which  may  be 
intermediate  steps  in  the  synthesis  of  fat  from  simpler  carbon 
compounds,  or,  on  the  other  hand,  may  arise  during  the  partial 
breaking  up  of  the  carbon  chain  in  the  feed  fat  which  probably 
precedes  its  transformation  into  milk  fat. 

As  a  general  conclusion,  therefore,  it  may  be  stated  that  the 
fat  of  milk  may  have  its  origin  either  in  the  fat  or  in  the  carbo- 
hydrates of  the  feed,  or  in  both.  Whether  it  may  also  be  pro- 
duced from  protein  has  not  been  demonstrated  experimentally, 
but  reasoning  by  analogy  with  the  formation  of  body  fat,  it 
must  be  regarded  as  at  least  very  probable. 

554.  Origin  of  lactose.  —  The  lactose  of  milk  is  a  disaccharid 
yielding  upon  hydration  dextrose  and  galactose.  Dextrose  or 
its  derivatives  are  abundant  in  the  feed  of  herbivorous  animals 
and  it  is  also  a  constant  ingredient  of  the  blood.  On  the  other 


468  NUTRITION  OF  FARM  ANIMALS 

hand,  while  the  ordinary  feed  of  herbivora  contains  carbohy- 
drates yielding  galactose,  the  latter  is  apparently  transformed 
into  glycogen  quite  promptly  and  at  any  rate  has  not  been 
found  in  the  blood,  while  animals  receiving  feed  containing  no 
galactose  (carnivora,  e.g.)  produce  lactose  in  their  milk.  The 
probability  seems  to  be  that  the  galactose  half  of  the  lactose 
is  manufactured  in  the  milk  gland  from  the  dextrose  of  the 
blood. 

555.  Sources  of  ash.  —  The  ash  ingredients  of   the  milk, 
including  its  sulphur  and  phosphorus,  are,  of  course,  derived 
ultimately  from  the  corresponding  ingredients  of  the  feed.     In 
liberal  milk  production  on  ordinary  winter  rations  containing 
a  sufficiency  of  organic  nutrients,  however,  it  appears  from  in- 
vestigations by  Forbes  1  that  considerable  amounts  of  calcium, 
magnesium  and  phosphorus  may  be  drawn  from  the  relatively 
large  store  contained  in  the  body,  presumably  to  be  replaced 
in  later  stages  of  lactation. 

556.  Character  of  milk  production.  —  While  the  statement 
that  milk  production  is  a  form  of  tissue  growth  is  probably 
incorrect  anatomically,  it  is  essentially  true  so  far  as  the  chemical 
composition  of  the  product  and  the  demands  which  it  makes 
on  the  feed  supply  are  concerned.     This  is  clearly  shown  by 
comparing  the  ratio  of  protein  to  fat  in  the  organic  matter  of 
milk  and  in  that  of  the  increase  in  weight  of  growing  animals. 
In  the  solids  of  milk,  it  is  evident  that  in  order  to  make  a  fair 
comparison  its  milk  sugar  should  be  reduced  to  the  equivalent 
amount  of  fat.     Taking  Babcock's  figures  (547)  as  representing 
the  average  composition  of  milk,  the  4.88  per  cent  of  sugar  di- 
vided by  2.25  is  equivalent  to  2.17  per  cent  of  fat,  which  added 
to  the  3.69  per  cent  of  fat  present  as  such  makes  a  total  fat 
equivalent  of  5.86  per  cent,  while  if  milk  sugar  were  thus  re- 
placed by  fat  the  total  organic  matter  would  amount  to  9.41 
per  cent.     On  this  basis,  100  parts  of  organic  matter  would 
contain  37.73  per  cent  of  protein  and  62.27  per  cent  of  fat. 
Comparing  these  figures  with  those  given  in  Chapter  XI  (458) 
for  the  composition  of  the  increase  in  growth,  it  appears  that 
the  proportion  of  protein  to  fat  is  greater  than  that  computed 
for  young  animals  except  in  the  earliest  stages  of  growth. 

The  computed  energy  content  of  average  milk  solids  is  2620 

1  Ohio  Expt.  Sta.,  Bui.  295  (1916). 


MILK  PRODUCTION  469 

Cals.  per  pound.  This  is  greater  than  the  energy  content  of 
the  dry  matter  gained  by  very  young  animals,  but  less  than 
that  computed  in  later  stages  of  growth.  In  a  general  way, 
then,  it  may  be  said  that  milk  solids  correspond  in  proportion 
of  protein  and  in  energy  value  per  pound  to  the  gains  made  by 
growing  animals  when  in  the  neighborhood  of  three  months  old. 

557.  Rate  of  production  of  milk  solids.  —  A  beef  calf  three 
months  old  may  be  assumed  to  make  a  growth  of  approximately 
1.5  pounds  per  day,  containing  perhaps  three-fourths  of  a  pound 
of  dry  matter  with  an  energy  content  of  about  2200  Cals. 
The  very  moderate  yield  of  15  pounds  of  average  milk  per 
day  would  contain  about  1.92  pounds  of  total  solids  equiva- 
lent to  5030  Cals.  of  energy.     In  other  words,  considerably 
more  than  twice  as  great  a  production  would  be  effected  by  the 
relatively  small  bulk  of  the  secreting  cells  in  the  udder  as  by 
the  whole  body  of  the  calf.     When  it  is  further  considered 
that  the  product  of  the  dairy  cow  is   all   edible,  her  great 
economic  value  as  a  producer  of  human  food  becomes  ob- 
vious.    On  this  point  Jordan  says : l  "  A  cow  yielding  6000 
pounds  of   average   milk   per   year   is    not   regarded  as  an 
unusual  animal.     This  means,  however,  the  annual  produc- 
tion of  not  less  than  780  pounds  of  milk-solids,  an  amount 
at  least  double  the  dry  matter  in  the  body  of  a  cow  weighing 
900  pounds.     When  we  consider  that  this  manufacture  of  new 
material  is  carried  on  not  only  during  a  single  year,  but  through 
the  entire  adult  life  of  the  animal,  we  begin  to  realize  how  ex- 
tensive are  the  demands  upon  the  food  supply.     Still  more 
striking  is  the  case  of  high-grade  cows  yielding  annually  over 
half  a  ton  of  milk  solids,  and  when  we  remember  the  perform- 
ance of  Clothilde,  whose  26,000  pounds  of  milk  produced  in 
a  year  certainly  contained  more  than   2500   pounds  of  solid 
matter,  we  must  regard  the  cow  as  possessing  wonderful  powers 
of  transmutation.     Her  capacity  for  the  rapid  and  economical 
production  of  human  food  of  the  highest  quality  is  not  equaled 
by  any  other  animal." 

558.  Factors  of  milk  production.  —  Milk  production  differs 
from  meat  production  in  one  very  essential  particular.     In  the 
latter,  broadly  speaking,  an  increase  in  the  whole  body  of  the 
animal  is  what  is  sought,  and  while  the  product  may  vary  in 

1  The  Feeding  of  Animals,  1908,  p.  308. 


470  NUTRITION  OF  FARM  ANIMALS 

market  quality,  all  the  feed  consumed  in  excess  of  the  main- 
tenance requirement  is  available  for  the  production  of  gain. 
In  milk  production,  on  the  contrary,  what  is  desired  is  the 
secretion  of  a  single  set  of  glands.  An  increase  in  weight  in 
the  mature  dairy  cow  is  not  sought.  At  best  it  represents  a 
diversion  of  feed  to  other  purposes  than  the  one  in  view,  while 
any  considerable  fattening  tends  to  check  the  activity  of  the 
milk  glands.  In  feeding  for  milk  production,  therefore,  it  is 
necessary  to  consider  not  only  the  surplus  feed  above  the  main- 
tenance requirement  but  the  factors  affecting  the  distribution 
of  that  surplus  between  milk  production  on  the  one  hand  and 
growth  or  fattening  on  the  other  hand.  The  art  of  feeding  for 
milk  consists  in  stimulating  the  milk  production  to  the  greatest 
economically  possible  extent  and  in  supplying  the  feed  material 
necessary  for  this  production,  while  avoiding,  in  the  mature 
animal,  any  material  increase  of  body  tissue. 

The  factors  governing  milk  production  are  essentially  the 
same  as  in  other  branches  of  animal  production,  viz.,  the  ani- 
mal, the  environment  and  the  feed  supply. 

In  milk  production,  however,  the  relative  importance  of  the 
first  and  second  conditions  is  greater  than  in  other  forms  of 
production  for  the  reason  that  they  may  materially  influence 
the  distribution  of  the  excess  feed  between  milk  production  and 
tissue  increase. 

§  2.   THE  ANIMAL  AS  A  FACTOR  IN  MILK  PRODUCTION 

559.  The  prime  factor  in  successful  dairy  production  is  the 
animal.     Unless  the  latter  possesses  abundant  secreting  tissue 
which  is  capable  of  being  stimulated  to  a  normal  rate  of  activity 
and  of  yielding  a  secretion  of  good  quality,  the  most  scrupulous 
care  and  the  most  abundant  feeding  will  inevitably  fail  to  yield 
satisfactory  returns. 

Individuality 

560.  Includes    breed    differences.  —  The    influence    of    in- 
dividuality may  be  said  to  include  that  of  breed,  since  a  breed 
is  simply  an  aggregate  of  more  or  less  similar  and  genetically 
related  individuals.     It  is  outside  the  scope  of  this  work  to 
discuss  problems  of  breeds  and  breeding,  and  this  branch  of  the 


MILK  PRODUCTION 


471 


subject  will  therefore  be  considered  mainly  from  the  point  of 
view  of  individual  differences. 

561.  Influence  on  yield  of  milk.  —  While  the  actual  quantity 
of  milk  produced  is  affected  by  feed,  care  and  other  circum- 
stances, the  capacity  of  the  animal  as  a  milk  producer  is  an 
individual  characteristic.  Just  as  the  maximum  speed  of 
which  a  horse  is  capable  is  dependent  primarily  upon  his  con- 
formation, spirit  and  other  individual  characteristics,  while 
the  actual  rate  at  which  he  travels  at  any  given  time  is  largely 
dependent  upon  his  driver,  so  the  maximum  capacity  of  the 
milk  cow  constitutes  an  individual  limit  beyond  which  she  can- 
not be  pushed  by  any  amount  of  care  or  feed. 

Striking  illustrations  of  the  importance  of  individuality  are  afforded 
by  the  various  public  tests  of  dairy  cows.  For  example,  in  the 
World's  Columbian  Exposition  of  1893,  the  conditions  of  the  so-called 
ninety-days  test  were  such  as  to  induce  liberal  feeding  and  the  best 
of  care  on  the  part  of  the  exhibitors.  The  cows,  numbering  74,  were 
of  three  different  breeds  and  presumably  represented  the  best  avail- 
able specimens  of  each  breed. 

The  following  table  shows  the  average  daily  product  of  the  best 1 
and  the  poorest  cow  of  each  breed  in  that  test. 

TABLE  123.  —  AVERAGE  DAILY  YIELD  OF  Cows  IN  NINETY-DAYS  TEST, 
WORLD'S  COLUMBIAN  EXPOSITION  2 


MILK 

FAT  OF  MILK 

TOTAL  SOLIDS 
OF  MILK 

Best  Jersey     

4.0.4.  Ib. 

1.98  Ib. 

5.67  Ib. 

Poorest  Jersey 

22  9  Ib 

i  09  Ib 

3  21  Ib 

Poorest  in  per  cent  of  best     . 
Best  Guernsey 

56.7% 
•2Q  o  Ib 

55-i% 
i  70  Ib 

56.6% 

r  20  Ib 

Poorest  Guernsey    
Poorest  in  per  cent  of  best 

Best  Shorthorn   

19.3  Ib. 
49-5  % 

40.9  Ib. 

0.97  Ib. 
57-1  % 

1.49  Ib. 

2.75  Ib. 
Si.o% 

<C.2Q  Ib. 

Poorest  Shorthorn 

27   Q   Ib 

o  80  Ib 

2  87  Ib. 

Poorest  in  per  cent  of  best     . 

58.4% 

53-7% 

54-3% 

1  By  best  and  poorest  cows  is  meant  those  which  showed  the  greatest  and  least 
net  profit  under  the  rules  of  the  test. 

2  Jersey  Bulletin,  Dec.  12,  1893. 


472  NUTRITION  OF  FARM   ANIMALS 

Even  the  lowest  of  these  records  are  remarkably  good  considering 
the  unfavorable  conditions  necessarily  incident  to  a  public  test.  In 
each  of  these  three  picked  herds,  however,  the  production  of  the 
poorest  animal  was  only  from  50  to  60  per  cent  of  that  of  the  best 
animal.  Moreover,  the  differences  between  individuals  of  the  same 
breed  were  much  greater  than  the  differences  between  the  averages 
for  the  three  breeds.  That  even  greater  differences  exist  among  the 
common  cows  of  the  country  has  been  shown  by  numerous  statistical 
investigations,  some  of  the  most  striking  of  which  have  been  col- 
lected by  Eckles.1 

562.  Influence  on  economy  of  feeding.  —  While  it  is  un- 
likely that  the  utilization  of  the  feed  in  the  narrower  sense 
(i.e.,  the  amount  of  milk  solids  of  a  given  composition  manu- 
factured in  the  udder  from  equal  amounts  of  nutritive  substances 
supplied)  is  materially  affected  by  the  individuality  of  the 
animal,  the  feed  utilization  in  the  broader  economic  sense  is 
very  largely  dependent  upon  this  factor.  It  must  be  con- 
stantly borne  in  mind  that,  as  already  stated  (558),  efficiency 
in  milk  production  is  in  large  part  a  question  of  the  distribution 
of  the  feed  supplied  in  excess  of  maintenance.  Some  animals, 
by  virtue  of  individual  or  inherited  peculiarities,  are  able  to 
transform  large  amounts  of  excess  feed  into  milk  without  stor- 
ing up  any  considerable  portion  of  it  in  the  form  of  body  tissue. 
Such  animals  tend  to  remain  spare  in  body  and  if  well  fed 
produce  large  amounts  of  milk.  They  are  the  typical  dairy 
animals.  Other  individuals,  on  the  contrary,  have  a  well- 
marked  tendency  in  the  opposite  direction,  viz.,  toward  the 
production  of  body  tissue.  When  fed  heavily,  they  utilize 
the  additional  feed  chiefly  in  this  direction  and  show  little  or 
no  tendency  toward  an  increase  in  milk  production.  These 
are  typical  meat-producing  animals.  The  two  types,  of  course, 
shade  into  each  other  by  imperceptible  gradations. 

The  important  bearing  of  these  facts  upon  the  nutrition  of 
dairy  animals  will  be  further  considered  later  (606-610). 
Here  it  may  simply  be  noted  that  the  superiority  of  cer- 
tain individuals  which  has  been  illustrated  in  the  preceding 
paragraphs  is  doubtless  due  to  a  considerable  extent  to  the 
ability  to  consume  large  amounts  of  feed  and  convert  the  sur- 
plus into  milk  rather  than  into  body  tissue. 

1  Dairy  Cattle  and  Milk  Production,  IQII,  pp.  118-126. 


MILK  PRODUCTION 


473 


563.  Influence  on  course  of  lactation.  —  That  individuality 
plays  an  important  part  in  determining  the  rate  at  which  the 
milk  yield  falls  off  with  advancing  lactation  is  shown  more 
specifically  in  a  subsequent  paragraph  (568). 

564.  Influence  on  composition  of  milk.  —  It  is  a  matter  of 
common  observation  that  cows  vary  as  regards  the  richness 
of  their  milk,  that  is,  as  regards  the  amount  of  cream  or  butter 
which  can  be  obtained  from  a  given  weight  of  milk.     Various 
breed  tests  at  experiment  stations  have  served  to  define  more 
exactly  the  influence  of  individuality  and  breed  upon  the  com- 
position of  milk.     The  results  cited  in  Table  1 24  are  intended 
to  illustrate  this  influence  and  not  primarily  to  compare  dif- 
ferent breeds.     The  table  shows  the  averages  of  the  results  ob- 
tained at  three  different  experiment  stations  1  for  several  breeds 
in  tests  covering  periods  of  time  ranging  from  eight  months  to 
two  years.     The  results  from  each  station  are  given  weight 
in  the  average  in  proportion  to  the  number  of  cows  under 
test,  and  the  average  results  are  arranged  in  the  order  of  the 
fat  content  of  the  milk. 

TABLE  124. —  AVERAGE  COMPOSITION  OF  MILK  OF  DIFFERENT  BREEDS 


ASH 

CASEIN 

AND 

ALBU- 
MIN 

LAC- 
TOSE 

FAT 

TOTAL 
SOLIDS 

NUM- 
BER OF 
Cows 
AVER- 
AGED 

Holderness  

068 

7  14. 

C  1  1 

3  46 

12.39 

2 

0.67 

3.22 

4.80 

3-S1 

12.  2O 

6 

Ayrshire 

o  67 

3  38 

51  3 

3  64 

12  82 

Shorthorn    

o  73 

3.27 

4.80 

3.6s 

12.4? 

7 

0.76 

3-74 

A.CA 

2 

Guernsey 

O  7  c 

3  78 

404 

A   06 

14  43 

e 

Jersey 

3.Q2 

4.08 

I4.QO 

8 

Fat  is  evidently  the  most  variable  ingredient  of  milk,  its 
maximum  exceeding  its  minimum  in  these  averages  by  more 
than  50  per  cent.  Along  with  the  increase  of  fat  there  is 


1  Maine  Expt.  Sta.,  Rpt.  1890,  p.  29 ;  New  Jersey  Expt.  Sta.,  Rpt.  1890,  pp.  223- 
224;  New  York  (Geneva)  Expt.  Sta.,  Rpt.  1891,  pp.  94-104. 


474 


NUTRITION  OF   FARM   ANIMALS 


also  an  increase  of  the  total  protein  and  of  the  total  solids, 
but  these  are  relatively  smaller  than  that  of  the  fat,  the  totals 
being  25  per  cent  and  21  per  cent,  respectively.  There  is  also 
an  increase  of  12  per  cent  in  the  proportion  of  ash,  while  the 
lactose,  on  the  contrary,  shows  comparatively  small  and  ir- 
regular changes,  the  extreme  range  of  the  differences  being 
ii  per  cent,  while  it  does  not  increase  regularly  with  the  in- 
crease of  the  other  ingredients.  The  lactose  is  evidently  the 
most  constant  ingredient  of  the  milk. 

565.  Influence  on  composition  of  milk  solids.  —  The  real 
nature  of  the  differences  in  composition,  however,  is  rendered 
clearer  by  computing  the  percentage  composition  of  the  water- 
free  total  solids,  with  the  results  shown  in  Table  125  :  — 

TABLE   125.  —  AVERAGE  COMPOSITION  OF  MILK  SOLIDS  OF  DIFFERENT 

BREEDS 


NUM- 

CASEIN 

BER  OF 

ASH 

AND 

LACTOSE 

FAT 

Cows 

ALBUMIN 

AVER- 

AGED 

Holderness 

5AQ 

2Z   A  A 

41  24 

27  Q3 

2 

Holstein-Friesian      

5-45 

26.2O 

39-79 

28.56 

6 

Ayrshire      

5-23 

26.37 

40.01 

28.39 

9 

Shorthorn 

5  86 

26  27 

*8.<;t; 

29  32 

Devon      

5-29 

26.04 

37.06 

3I.6l 

2 

Guernsey 

520 

26  20 

OA  2^ 

34  37 

Jersey 

26.31 

^^  4.2 

3  ^  24 

8 

From  the  foregoing  table,  it  appears  that  the  percentages  of 
ash  and  of  total  protein  in  the  milk  solids  are  very  constant, 
the  single  figures  differing  but  very  slightly  from  the  averages 
of  5.36  and  26.10,  respectively.  The  essential  difference  in 
the  composition  of  "the  milk  solids  lies  in  the  proportion  of 
lactose  to  fat,  the  former  decreasing  as  the  latter  increases, 
while  the  total  percentage  of  the  two  taken  together  is  prac- 
tically constant,  varying  less  than  0.7  per  cent  from  the  average 
of  68.53  Per  cent-  In  other  words,  it  appears  from  these  figures 
that  in  cows  producing  milk  rich  in  fat  the  secreting  cells  form 
relatively  less  lactose  and  correspondingly  more  fat,  while,  as 


MILK  PRODUCTION  475 

Table  124  shows,  this  difference  is  accompanied  by  a  rela- 
tively smaller  secretion  of  water,  so  that  the  percentage  of  total 
solids  in  the  resulting  milk  is  greater. 

Cooke,1  in  1890,  drew  the  same  conclusion  from  a  study  of 
over  2400  analyses  of  milk  reported  by  the  experiment  sta- 
tions of  the  United  States  up  to  that  date,  and  more  recently 
Haecker 2  has  reached  substantially  the  same  result  from 
analyses  of  544  individual  samples  of  milk  from  the  Minnesota 
Station  herd. 

566.  Variability  of  composition  in  same  animal.  —  It  should 
be  noted  that  the  foregoing  conclusions  are  drawn  from 
the  average  composition  of  the  milk  of  the  same  individuals 
for  comparatively  long  periods.  The  composition  of  the  milk 
of  the  same  cow,  however,  may  and  frequently  does  vary  quite 
widely  from  one  milking  to  another  without  affecting  its  average 
composition  as  computed  from  analyses  of  a  number  of  milkings. 

This  has  been  observed  especially  in  the  case  of  the  fat  be- 
cause far  more  determinations  have  been  made  of  this  con- 
stituent than  of  any  other,  the  fat  being  both  the  most  valuable 
and  the  most  easily  determinable  ingredient.  Variations  as 
great  as  i  per  cent  in  the  fat  content  of  successive  milkings  of 
the  same  cow  are  not  uncommon  and  differences  of  2  and  even 
3  per  cent  not  very  rare.  Whether  there  is  a  correlated  varia- 
tion in  the  proportion  of  lactose,  as  in  the  averages  compared 
in  the  previous  paragraph,  does  not  appear.  It  is  presumed 
that  these  variations  are  due  largely  to  external  influences  but 
no  definite  connection  with  any  specific  factors  of  environment 
has  been  traced  with  certainty,  although  Spier  3  believes  them 
to  be  due  to  incomplete  milking  (575) .  It  is  evident  that  correct 
comparisons  of  the  yields  of  different  animals,  or  of  the  same 
animal  at  different  times,  can  be  made  only  on  the  basis  of  the 
average  yield  and  composition  for  a  number  of  days. 

The  extent  of  this  variability  in  the  composition  of  milk  from 
one  milking  to  another  appears  to  be  an  individual  peculiarity, 
the  milk  of  some  cows  being  much  more  uniform  in  daily  com- 
position than  that  of  others.  An  interesting  example  of  this 
has  been  reported  by  Farrington.4 

1  Vt.  Expt.  Sta.,  Rpt.  1890,  pp.  97-100. 

2  Minn.  Expt.  Sta.,  Bui.  140  (1914),  p.  51. 

3  Jour.  Highland  and  Agr.  Soc.,  1909,  p.  287. 

4  Ills.  Expt.  Sta.,  Bui.  17  (1891),  p.  Q. 


476  NUTRITION  OF  FARM  ANIMALS 

Stage  of  lactation 

567.  Milk  production  a  periodic  function.  —  Milk  produc- 
tion has  as  its  object  the  nourishment  of  the  offspring.     In  a 
state  of  nature  it  is  a  periodic  function,  beginning  at  the  birth 
of  the  young  or  shortly  before,  while  as  the  young  animal  gradu- 
ally becomes  less  dependent  on  the  mother  it  diminishes  in 
intensity  and  finally  ceases.     Although  man  has  greatly  pro- 
longed the  period  of  milk  production  of  the  cow,  so  that  the 
time  during  which  she  goes  dry  is  relatively  short  and  in  some 
instances  is  eliminated  altogether,  nevertheless,  milk  production 
still  retains  its  periodic  character  and  undergoes  marked  changes 
during  the  progress  of  a  lactation. 

568.  Influence  on  yield  of  milk.  —  The  most  evident  effect 
of  advancing  lactation  is  the  gradual  decrease  of  the  amount 
of  milk  produced,  but  the  rate  of  decrease  may  differ  widely 
at  different  stages  in  the  same  animal  and  in  different  animals 
at  the  corresponding  period  in  lactation.     As  a  rule,  the  amount 
of  milk  does  not  reach  its  maximum  immediately  after  the  birth 
of  the  young,  but  shows  an  increase  for  one  or  two  weeks  in 
the  case  of  the  cow.     Following  this  maximum,  there  is  typi- 
cally a  slow  falling  off  for  several  months  followed  by  a  more 
rapid  decrease  as  the  time  of  the  next  calving  approaches,  all  but 
exceptional  Cows  going  dry  for  a  longer  or  shorter  time.     In  the 
case  of  farrow  cows,  the  milk  production  may  continue  to  show 
a  comparatively  slow  decrease  for  a  much  longer  time. 

The  curves  of  lactation  as  they  may  be  called,  however,  vary 
greatly  from  cow  to  cow  and  from  year  to  year  with  the  same 
animal  and  show  marked  irregularities  often  not  readily  ex- 
plained by  any  observed  conditions. 

569.  Influence   on   composition   of  milk.  —  In  general   the 
percentages  of  total  solids  and  of  fat  tend  to  increase,  especially 
toward  the  end  of  lactation  when  the  quantity  of  milk  falls  off 
rapidly.     Like  the  changes  in  quantity,   these  variations  in 
composition  are  often  irregular  and  sometimes  are  scarcely 
manifest  at  all  until  the  rapid  falling  off  in  quantity  sets  in 
toward  the  end  of  the  lactation. 

570.  Bearing  on  experimental  methods.  —  The  unavoidable 
changes  in  the  yield  and  composition  of  milk  with  the  advance 
of  lactation  must  be  taken  account  of  jn  all  experiments  on 


MILK  PRODUCTION  477 

milk  production,  and  render  the  interpretation  of  their  results 
peculiarly  difficult.  It  is  obvious,  e.g.,  that  if  a  change  of  the 
ration  of  a  cow  is  accompanied  by  a  decrease  in  her  milk  yield 
part  at  least  of  the  decrease  may  be  due  to  the- progress  of  lac- 
tation and  not  to  the  change  of  feed.  On  the  other  hand  an 
increase  of  the  milk  yield  in  a  later  period  of  the  experiment 
may  be  partly  offset  by  the  natural  shrinkage  in  milk.  In 
brief  the  later  periods  of  an  experiment  are  at  a  disadvantage 
compared  with  the  earlier  periods. 

Two  methods  for  eliminating  or  attempting  to  eliminate  this 
influence  of  lactation  have  been  used,  viz.,  the  period  system 
and  the  group  system. 

571.  The  period  system.  —  In  the  period  system,  as  intro- 
duced by  Wolff,  Klihn  and  others  of  the  earlier  experimenters, 
the  animal  receives  an  identical  ration  in  two  or  more  periods 
well  removed  from  each  other  in  point  of  time  —  usually  the 
first  and  last  periods  —  and  from  the  results  of  these  periods  the 
average  daily  rate  of  decrease  in  the  yield  of  milk  and  its  in- 
gredients is  calculated.     On  the  assumption  that  had  the  same 
ration  or  treatment  been  continued  unchanged  this  rate  would 
have  been   uniform   throughout   the   experiment,   it  may  be 
computed  what  yields  would  have  been  secured  in  the  inter- 
mediate periods.     A  comparison  of  these  computed  yields  with 
those  actually  observed  is  taken  as  the  measure  of  the  effect 
of  the  change  in  feed  or  other  conditions.     The  accuracy  of 
this  method  depends  of  course  on  the  correctness  of  the  as- 
sumption that  the  yields  would  have  decreased  at  a  uniform 
rate. 

572.  The  group  system.  —  The  use  of  the  group  system  was 
introduced  by  Fjord  and  his  successors  in  the  Copenhagen 
Experiment  Station  in  connection  with  their  determinations  of 
the  so-called  feed  units  (702).     The  period  system  seeks  to 
compare  each  animal  with  itself.     The  group  system,  on  the 
other  hand,  attempts  to  compare  an  animal  or  group  with  an- 
other check  animal  or  group.     In  a  long  preliminary  period 
both  groups  receive  the  same  ration  or  treatment  and  their 
relative  production  is  determined.     One  of  the  groups  is  then 
continued  on  the  same  treatment  while  with  the  other  group 
the  factor  to  be  tested  is  introduced.     Finally,  in  a  concluding 
period,  both  groups  are  again  treated  as  in  the  initial  period. 


478  NUTRITION  OF  FARM   ANIMALS 

A  combination  of  the  two  systems  may  also  be  used,  one 
group  of  animals  being  fed  varying  rations  in  successive  periods, 
while  the  other  receives  a  uniform  ration  throughout  the  entire 
experiment. 

A  very  complete  discussion  of  the  methods  of  eliminating  the  in- 
fluence of  advancing  lactation  in  the  interpretation  of  the  results  of 
experiments  on  milk  production  is  to  be  found  in  a  recent  article  by 
Morgen.1 

§  3.  THE  INFLUENCE  OF  ENVIRONMENT  ON  MILK  PRODUC- 
TION 

The  word  environment  is  here  used  loosely  as  a  convenient 
term  to  summarize  all  those  external  influences  other  than  feed 
which  may  affect  milk  production.  The  dairy  cow  appears 
to  be  particularly  sensitive  to  external  conditions,  some  of  the 
more  important  of  which  are  considered  in  the  following  para- 
graphs. 

Milking 

Milking  is  but  an  imperfect  imitation  of  the  suckling  of  the 
young,  and  naturally  its  efficiency  in  securing  the  milk  is  likely 
to  be  affected  by  a  variety  of  circumstances. 

573.  Frequency  of  milking.  —  As  already  stated,  the  cavities 
of  the  udder  in  heavy  milkers  cannot  hold  all  the  milk  produced 
at  one  milking.  Between  milkings  there  evidently  may  be  a 
considerable  accumulation  of  matter  in  the  alveoli  and  canals 
which  appears  to  have  the  effect  of  diminishing  the  secreting 
activity  of  the  epithelial  cells  through  what  might  be  crudely 
called  "  back  pressure."  Suckling  or  milking  would  have  the 
effect  of  relieving  this  "  pressure "  and  perhaps  rendering 
secretion  more  easy,  while  at  the  same  time  it  seems  to  act  as  a 
direct  stimulus  to  secretion.  At  any  rate  it  is  a  fact  that  more 
frequent  milking  tends  to  increase  the  yield  of  milk,  especially 
in  the  case  of  good  cows  and  in  the  earlier  stages  of  lactation. 
The  effect  of  frequent  milking  is  strikingly  illustrated  in  the 
following  experiments  by  Kaull.2  The  abrupt  falling  off  in  the 
milk  yield  when  the  milking  was  made  very  frequent  may  per- 

1  Landw.  Vers.  Stat.,  77  (1912),  351. 

2  Cited  by  Kellner,  Die  Ernahrung  der  landw.  Nutztiere,  6th  Ed.,  p.  521. 


MILK  PRODUCTION 


479 


haps  be  interpreted  as  due  to  overstimulation   or   mechanical 
irritation  of  the  udder. 

TABLE  126. — EFFECT  OF  FREQUENT  MILKING 


TOTAL  QUANTITY 
or  MILK  PER 
MILKING 

TOTAL  QUANTITY 
OF  MILK  IN  24 
HOURS 

Milking  every  24  hr 

^?  81  Kff 

7  62  Ke 

Milking  every  2  hr  

2  4.6  KfiT 

o  84.  Ker 

Milking  every  4  hr  
Milking  every  2  hr 

2.06  Kg. 
in  Kg 

12.36  Kg. 
1  2  -2  2  KET 

Milking  every  65  min  

0.66  Kg. 

14..  62  Kg 

Milking  every  50  min  

0.07  Kg. 

2.O2  Kg. 

Results  obtained  in  short  experiments,  however,  give  an 
altogether  exaggerated  idea  of  the  practical  advantage  of  fre- 
quent milking.  As  Fleischmann  has  shown,  the  capacity  of 
the  udder  adjusts  itself  quite  definitely  to  its  productive  activity 
and  in  the  measure  in  which  this  takes  place  the  gain  due  to 
more  frequent  milking  diminishes  or  disappears.  He  estimates 
the  increased  yield  obtained  by  three  as  compared  with  two  daily 
milkings  at  about  6  or  7  per  cent.  In  many  cases,  therefore, 
it  will  be  questionable  whether  the  additional  milk  obtained  by 
a  third  milking  will  be  at  all  sufficient  to  pay  for  the  extra  labor 
involved.  In  the  case  of  very  productive  cows  in  the  earlier 
stages  of  lactation  more  frequent  milking  may  be  necessary, 
not  so  much  for  the  sake  of  obtaining  the  extra  milk  as  for  the 
sake  of  avoiding  inflammatory  conditions  in  the  udder  and  es- 
pecially for  preventing  the  permanent  depression  of  the  secret- 
ing power  which  would  follow  incomplete  milking  and  which 
would  mean  a  loss  of  milk  throughout  the  whole  lactation. 

574.  Influence  of  frequent  milking  on  composition  of  milk.  — 
Frequent  milking  tends  to  increase  the  percentage  of  solids  and 
of  fat  in  the  milk.  This  effect  is  manifest  especially  when  the 
intervals  between  the  milkings  are  of  unequal  length. 

When  milking  takes  place  at  regular  intervals,  the  several 
milkings  tend  to  have  about  the  same  average  composition. 
If  the  intervals  vary  in  length,  the  milk  obtained  after  the 
shorter  interval  on  the  average  contains  a  higher  percentage  of 


480  NUTRITION  OF  FARM  ANIMALS 

solids  and  of  fat,  i.e.,  it  is  more  concentrated  than  that  yielded 
after  the  longer  interval.  The  differences  in  the  composition 
of  the  night's  and  morning's  milk,  which  have  been  the  subject 
of  so  much  discussion,  appear  explicable  upon  this  basis,  the 
interval  between  the  morning's  and  night's  milking  being  usually 
less  than  that  between  the  night's  and  morning's. 

575.  Completeness  of  milking.  —  If  successive  portions  of 
the  same  milking  be  analyzed,  the  percentage  of  fat  in  the  later 
portions  will  be  found  to  be  greater  than  in  the  earlier  ones, 
while  the  percentage  of  solids-not-fat  varies  comparatively 
little.  The  fact  of  the  greater  richness  of  the  so-called  "  strip- 
pings  "  is  well  known.  This  difference  was  at  one  time  ex- 
plained as  caused  by  an  actual  rising  of  the  cream  on  the  milk 
contained  in  the  udder.  The  fact,  however,  that  but  a  com- 
paratively small  amount  of  milk  is  held  in  the  milk  cistern,  as 
well  as  the  entire  anatomy  of  the  udder,  renders  this  explanation 
untenable.  The  difference  is  probably  due  to  a  partial  retention 
or  stagnation  of  the  fat  globules  in  the  alveoli  and  canals,  they 
being  afterward  washed  out  by  the  portions  of  milk  secreted 
during  the  latter  part  of  the  milking.  Incomplete  milking 
not  only  fails  to  get  this  fat,  thus  lowering  the  quality  of  the 
milk  actually  obtained  (compare  566),  but  it  appears  that 
the  retention  of  the  fat  in  the  alveoli  tends  to  check  the 
secretion  of  the  milk.  In  all  forms  of  milking,  therefore,  it 
is  important  that  the  cow  be  milked  out  as  completely  as 
practicable.  The  advantages  of  various  methods  of  manipulat- 
ing the  udder,  such  as  the  Hegelund  method,  are  probably  due 
largely  to  this  influence.  Similarly,  in  the  use  of  milking  ma-« 
chines  it  seems  to  be  necessary  with  most  cows  to  remove 
the  last  portions,  or  strippings,  by  hand. 

Muscular  exertion  —  exercise,  fatigue 

The  influence  of  muscular  exertion  upon  milk  secretion  has 
been  much  discussed  upon  a  comparatively  slender  experi- 
mental basis.  In  the  United  States  the  question  has  usually 
been  as  to  the  desirability  of  allowing  freedom  of  motion  and 
exercise  to  dairy  cows,  while  in  Europe,  especially  among 
small  farmers,  cows  are  used  for  draft  to  a  not  inconsiderable 
extent. 


MILK  PRODUCTION  481 

576.  Feed  cost  of  exercise.  —  Attention  was  called  in  the 
discussion  of  the  maintenance  requirement  in  Chapter  VIII 
(391)  to  the  very  marked  effect  of  muscular  exertion  in  increas- 
ing the  katabolism,  especially  of  body  fat  or  of  the  non-nitroge- 
nous ingredients  supplied  by  the  feed.    It  has  been  frequently  ar- 
gued from  this  fact  that  the  amount  of  exercise  allowed  to  dairy 
cows  should  be  restricted  as  much  as  possible.     Not  a  few  dairy- 
men indeed  have  gone  so  far  as  to  confine  their  cows  entirely, 
reasoning  that  since  the  object  of  their  business  is  to  convert 
feed  into  milk  any  diversion  of  it  to  the  support  of  muscular 
exertion  was  a  waste.     This,  however,  is    a   very  narrow  and 
inadequate  view  of  the  subject.     Most  authorities  on  dairying 
regard  a  moderate  amount  of  exercise  for  dairy  cows  as  bene- 
ficial.    Thus  Martiny  1  in  1871  cites  five  authorities  on  this 
point  and  expresses  the  opinion  that  exercise  and  moderate 
work  increase  rather  than   decrease  the  yield  of  milk,  while 
severe  work  has  an  unfavorable  effect  upon  both  the  yield  and 
quality.     Similar  opinions  are  expressed  later  by  C.  F.  Miiller, 
Fleischmann,  Kirchner,  Kb'nig  and  Von  Klenze.     These  earlier 
data  are  of  the  nature  of  more  or  less  empirical  observations 
rather  than  of  actual  experiments. 

577.  Morgen's  investigations.  —  Of  actual  experiments  upon 
the   influence    of    muscular    exertion    upon    milk  production, 
those  of  Morgen2  at  the  Hohenheim  Experiment  Station  are 
the  most  convincing  because  they  were  made  under  strictly 
comparable    conditions    and    especially    because    the    relative 
amounts   of    work    performed   in   the   different   periods  were 
determined. 

The  two  Simmenthal  cows  employed  were  accustomed  to 
being  used  for  draft.  The  work  was  done  at  a  slow  walk  upon 
the  sweep  power  dynamometer  used  by  Wolff  in  his  experiments 
upon  work  production  by  the  horse  (386  a,  670,  779),  the  amount 
of  work  performed  being  regulated  in  part  by  the  resistance  of 
the  dynamometer  and  in  part  by  the  number  of  hours  of  work 
required,  so  that  approximately  single,  double  and  quadruple 
work  was  done.  The  ration  fed,  which  was  a  liberal  one,  was 
unchanged  throughout  the  trials.  The  experiment  consisted 
of  1 1  periods,  approximating  two  weeks 3  each  of  alternate  rest 

1  Die  Milch,  Part  I,  pp.  345-435-  *  Landw.  Vers.  Stat.,  51  (1899),  117. 

3  Eleven  to  twenty-six  days. 
2  I 


482  NUTRITION  OF  FARM  ANIMALS 

and  work  periods,  beginning  with  a  rest  period,  so  that  each 
work  period  was  preceded  and  followed  by  a  rest  period. 

The  rather  moderate  amount  of  work  performed  caused  some 
decrease  in  the  volume  of  milk  produced,  the  effect  tending  to 
be  a  little  greater  in  the  periods  in  which  most  work  was  done. 
The  decrease,  however,  was  chiefly  a  decrease  in  the  amount 
of  water  secreted,  although  a  slight  diminution  in  the  yield  of 
total  milk  solids,  ranging  from  10  to  85  grams  per  day,  was  ob- 
served. In  other  words,  the  effect  of  the  work  was  to  render 
the  milk  somewhat  more  concentrated.  The  most  notable 
effect,  however,  was  upon  the  yield  of,  fat,  which  showed  an 
actual  increase  in  every  case  but  two.  This  increase  was  com- 
pensated for  by  a  decrease  of  the  fat-free  solids,  so  that  analyses 
of  the  milk  showed  a  higher  percentage  of  fat  and  of  total  solids, 
while  the  percentage  of  fat-free  solids  remained  practically  un- 
changed. 

578.  Confirmatory  results.  —  Quite  similar  results,  although 
obtained  in  some  cases  by  less  rigorous  methods,  have  been 
reported  by  Domic,1  Stillich,2  Backhaus,3  Torssell 4  and  Dol- 
gich.5 

Observations  by  Sturtevant,6  Henkel 7  and  Hills 8  upon  the 
effect  of  fatigue  on  the  yield  and  composition  of  milk  are  also 
in  accord  with  the  results  of  experiments  upon  work  and  ex- 
ercise in  showing  a  tendency  to  reduce  the  quantity  of  milk 
and  at  the  same  time  to  increase  both  the  percentage  and  the 
actual  yield  of  fat. 

Aside  from  the  question  of  the  effects  of  overexertion,  it 
appears  clear  that  a  considerable  amount  of  work  may  be  per- 
formed by  cows  without  any  serious  diminution  of  the  volume 
of  their  milk  and  with  an  actual  increase  in  the  yield  of  fat,  its 
most  valuable  ingredient.  The  lightest  work  in  Morgen's 
experiments  was  roughly  equivalent  to  hauling  a  load  of  a  ton 
if  miles  over  a  smooth  level  road.  This  is  certainly  much  more 
labor  than  the  ordinary  cow  will  perform  when  turned  loose  in 
a  comfortable  yard  or  paddock. 

1  Milch  Ztg.,  25  (1896),  331-  2  Jahresber.  Agr.  Chem.,  39  (1897),  529. 

3  Centbl.  Agr.  Chem.,  28  (1899),  492;   Expt.  Sta.  Rec.,  10  (1899),  85. 

4  Expt.  Sta.  Rec.,  12  (1901),  381.  5  Jahresber.  Tier  Chem.,  33  (1904),  382. 
6N.  Y.  (Geneva)  Expt.  Sta.,  Rpt.  1882,  p.  25. 

7  Landw.  Vers.  Stat.,  46  (1896),  329. 

8Vt.  Expt.  Sta.,  Rpts.  1894,  p.  162,  1898,  p.  367  and  1899,  p.  309. 


MILK  PRODUCTION  483 

It  is  still  true,  of  course,  that  the  energy  for  all  muscular 
exertion  is  ultimately  supplied  by  the  feed.  In  the  instance 
just  mentioned  the  extra  feed  required  for  this  purpose  may 
be  approximately  estimated,  on  the  basis  of  the  data  contained  in 
Chapter  XIV,  at  two-thirds  of  a  pound  of  digestible  matter  per 
day,  equal  to  about  eight- tenths  of  a  pound  of  maize.  The  feed 
cost  of  the  exercise  ordinarily  taken  by  cows  turned  out  in  the 
yard  must  be  insignificant  and  be  far  outweighed  by  the  tonic 
effects  of  fresh  air,  sunshine  and  freedom  on  their  health  and 
general  condition,  while  in  the  case  of  heavily  fed  cows  some 
exercise  may  possibly  be  of  advantage  in  diminishing  the  tend- 
ency to  fatten.  The  question  of  turning  out  dairy  cows  for 
exercise,  then,  virtually  reduces  itself  to  the  question  whether 
the  cost  of  the  labor  involved  is  repaid  by  the  effect  upon 
the  health  of  the  animals. 

Temperature.    Shelter 

579.  Air  temperature.  —  The  general  principles  regarding 
the  relations  between  external  temperature,  heat  production 
and  feed  supply,  already  discussed  in  Chapters  VII  (350-356), 
VIII  (395-397)  and  XII  (535-543),  apply  also  to  the  dairy  cow. 
Like  the  beef  steer,  the  well-fed  dairy  cow  in  full  flow  of  milk  is 
consuming  a  large  excess  of  feed  above  her  maintenance  ration 
and  is  producing  a  correspondingly  large  amount  of  heat. 

For  example,  in  an  experiment  reported  by  Jordan  1  the  computed 
heat  production  of  two  cows  (disregarding  slight  changes  in  weight) 
and  the  estimated  amount  of  heat  which  would  have  been  produced 
on  a  maintenance  ration  were  as  follows :  — 

TABLE  127.  —  ESTIMATED  HEAT  PRODUCTION  OF  Cows 

Cow  No.  10  Cow  No.  12 

Weight 775  Lb.  1200  Lb. 

Computed  heat  production    .     .         18.67  Therms  21.10  Therms 
Estimated   heat   production   on 

maintenance  ration    .     .     .     .         10.10  Therms  13.70  Therms 

The  heat  production  was  greater  in  one  case  by  85  per  cent  and 
in  the  other  by  54  per  cent  than  the  estimated  amount  on  maintenance, 
which  is  a  considerably  greater  excess  than  that  computed  (537)  for 
Kellner's  fattening  steers. 

1  The  Feeding  of  Animals,  The  Macmillan  Co.,  New  York,  1908,  p.  310. 


484  NUTRITION  OF  FARM   ANIMALS 

So  far  as  mere  maintenance  of  body  temperature  goes,  then, 
no  reason  appears  why  a  cow  might  not  be  subjected  to  com- 
paratively low  temperatures  without  causing  any  increased 
katabolism  for  the  sake  of  heat  production  solely.  That  the 
same  factors  of  size  and  weight,  humidity  of  air,  and  the  amount 
and  character  of  ration  as  in  the  case  of  the  steer  enter  into  the 
question  is  obvious. 

580.  Shelter,  etc.  —  The  question  of  shelter  does  not  differ 
in  principle  with  the  cow  and  with  the  steer.     The  influence  of 
precipitation,   wind,   insolation   and   temperature   of   drinking 
water  are  the  same  qualitatively  on  the  cow  as  on  the  steer  and 
the  same  reasons  which  render  shelter  desirable  in  the  one  ca^e 
apply  in  the  other. 

581.  Modifying  factors.  — The  foregoing  facts,  however,  are 
scarcely  sufficient  to  justify  the  conclusion  that  a  dairy  cow 
may  be  treated  in  this  respect  like  a  beef  steer.     In  making  a 
quantitative   application   of   these   facts   in   practice,    certain 
modifying  factors  require  consideration. 

Relative  body  surface.  —  Even  the  most  casual  comparison 
of  the  dairy  cow  with  the  beef  steer  is  sufficient  to  show  that 
they  differ  materially  in  form  and  to  raise  the  supposition  that 
the  ratio  of  body  surface  to  weight  may  vary  considerably  in 
the  two  types.  The  writer  is  not  aware  of  any  measurements 
of  body  surface  of  cows  but  one  can  hardly  avoid  the  impression 
that  the  spare  angular  form  of  the  typical  dairy  cow  exposes 
relatively  more  surface  than  the  compact,  rounded  form  of  the 
beef  animal. 

Condition.  —  Outdoor  winter  feeding  of  cattle  is  practiced 
largely  with  fattening  animals  and  it  is  with  them  that  most 
experiments  have  been  conducted.  With  such  an  animal  a 
considerable  covering  of  fat  is  usually  acquired  before  the  onset 
of  extreme  cold  weather,  while  the  typical  dairy  cow  devotes  her 
feed  to  milk  production  and  carries  very  little  body  fat.  There 
are  no  definite  data  as  to  the  protective  value  of  a  fat  covering 
but  doubtless  it  is  a  poor  conductor  of  heat  and  it  would  seem 
that  it  might  have  considerable  influence  in  reducing  radiation. 

Skin  and  hair.  —  The  skin  of  the  dairy  cow  is  reputed  to  be 
thinner  than  that  of  the  steer  and  may  therefore  be  a  better 
radiator  of  heat.  The  coat  of  hair  of  the  cow,  too,  is  apt  to  be 
shorter  and  lighter  than  that  of  the  steer,  whether  as  a  result 


MILK  PRODUCTION  485 

of  breeding  or  of  continuous  shelter  and  warm  quarters,  and  is 
to  that  extent  a  poorer  protection  against  loss  of  heat. 

For  all  these  reasons,  it  is  clear  that  the  loss  of  heat  from  the 
dairy  cow  may  well  be  more  rapid  than  that  from  the  steer  of 
like  weight  under  the  same  external  conditions  and  that  con- 
sequently the  minimum  limit  of  external  temperature  below 
which  additional  katabolism  is  caused  may  be  higher  for  the 
former  than  for  the  latter. 

582.  The    direction    of    production.  —  Another    important 
consideration  in  connection  with  the  question  of  temperature 
and  shelter  for  dairy  cows  is  that  of  their  possible   influence 
upon  the  direction  of  production.     Stress  was  laid  at  the  outset 
of  this  discussion  of  the  factors  of  milk  production  (558)  upon 
the  essential  difference  between  beef  production  and  milk  pro- 
duction due  to  the  fact  that  in  the  latter  it  is  simply  the  secre- 
tion of  a  single  gland  and  not  a  general  increase  of  the  whole 
body  which  is  desired.     The  activity  of  the  milk  gland,  how- 
ever, is  much  more  sensitive  to  external  influences  than,  for 
example,  that  of  adipose  tissue.     It  is  quite  conceivable,  there- 
fore, that  a  degree  of  cold  or  exposure  which,  from  the  standpoint 
of  heat  production  merely,  might  not  require  any  additional 
katabolism  to  maintain  the  body  temperature,  might  neverthe- 
less check  the  formation  of  milk,  especially  if  the  cow  were  sub- 
jected to  it  suddenly.     In  such  a  case  it  would  be  anticipated, 
either  that  feed  previously  used  for  milk  production  would  be 
stored  up  as  body  fat  or  else,  if  the  cow  continued  to  eat  the 
same  amount,  would  lead  to  a  stimulation  of  the  general  body 
katabolism  and  so  to  an  unnecessary  increase  in  heat  production. 

In  other  words,  exposure  to  cold  might  conceivably  neither 
increase  the  feed  consumption  nor  diminish  the  total  utilization 
of  surplus  feed  but  might,  nevertheless,  be  a  disadvantage  be- 
cause it  diverted  the  current  of  productive  activities  from  the 
formation  of  milk  to  other  and  undesired  forms  of  production. 

583.  Results  in  practice.  —  Only  meager  experimental  evi- 
dence is  available  regarding  the  practicable  or  desirable  limits 
of  temperature  for  dairy  cows. 

Plumb  r  compared  the  feed  consumption  and  milk  yield  of  two 
lots  of  purchased  cows,  one  of  which  was  turned  out  into  the  yard 
about  one  hour  per  day  on  sunny  days  while  the  other  was  turned 
1  Ind.  Expt.  Sta.,  Bui.  47  (1893),  pp.  89-96. 


486 


NUTRITION  OF  FARM  ANIMALS 


out  for  eight  hours  every  day  without  regard  to  the  weather  but  with 
some  shelter  from  the  wind.  The  cows  consumed  feed  ad  libitum. 
The  exposed  lot  ate  much  more  grain  but  somewhat  less  hay  than 
the  sheltered  lot  and  produced  161.1  pounds  more  milk.  No  proof  of 
the  comparability  of  the  two  lots  is  given. 

Brooks  1  exchanged  two  lots  of  cows  between  an  artificially  heated 
stable  kept  at  55°  F.  and  a  cooler,  unheated  one,  the  temperature  of 
which  is  not  reported.  Rather  more  milk  was  produced  in  the  warm 
stable  but  its  percentage  of  fat  was  lower. 

Richards  and  Jordan 2  recorded  the  milk  yield  of  a  number  of  cows 
upon  uniform  feed  in  alternate  periods  in  which  the  stable  tempera- 
ture was  maintained,  respectively,  at  about  45°  and  55°  F.  More 
milk  was  produced  in  three  cases  out  of  four  and  more  butter  fat  in 
two  cases  out  of  four  at  the  higher  temperature. 

Spier  3  reports  experiments  at  four  farms,  on  a  total  of  88  animals 
upon  the  relation  of  stable  temperature  and  ventilation  to  milk  yield. 
He  calls  attention  to  the  fact  that  both  these  factors  are  involved  in 
experiments  upon  the  influence  of  shelter.  The  following  table  shows 
the  results  obtained  in  two  specially  cold  periods  as  compared  with 
the  average  of  warmer  preceding  and  following  periods  and  likewise 
the  average  results  for  the  entire  experiments.  The  average  rations 
consumed  are  stated  but  there  is  no  record  of  actual  feed  consumed 
during  the  several  periods  nor  of  the  live  weights  of  the  animals. 

TABLE  128.  —  INFLUENCE  OF  VENTILATION  AND  STABLE  TEMPERATURE 
ON  MILK  PRODUCTION 


FREE  VENTILATION 

RESTRICTED  VENTILATION 

Milk  per 
Day  and 
Head 

Fat  in 
Milk 

Stable 
Temper- 
ature 

Milk  per 
Day  and 
Head 

Fat  in 
Milk 

Stable 
Temper- 
ature 

Lb. 

% 

°F. 

Lb.' 

% 

°F. 

Dec.  2O-Jan.  4 

Warm  periods    .     . 

2Q.O 

3-55 

53-76 

28.9 

3-48 

61.73 

Cold  period    .     .     . 

2Q.O 

3-5i 

41.20 

29.0 

3-53 

52.30 

Feb.  i4~Mar.  27 

Warm  periods     .     . 

25-3 

3-63 

50-3I 

25-4 

3-48 

60.  1  1 

Cold  period    .     .     . 

25-4 

3-69 

46.07 

25-5 

3-5i 

56.67 

Entire  Experiments 

Nov.  22-Mar.  27    . 

27-5 

3-55 

49.82 

27-3 

3-49 

59-40 

1  Mass.  (Hatch)  Expt.  Sta.,  Rpt.  1895,  p.  39. 

2  Wis.  Expt.  Sta.,  2ist  Rpt.,  1903-1904,  p.  143. 

3  Jour,  of  Highland  and  Agr.  Soc.,  1909,  pp.  255-306. 


MILK  PRODUCTION 


487 


The  foregoing  results  show  no  perceptible  effects  from  the  tem- 
perature fluctuations  within  the  range  of  these  experiments  either  on 
the  lots  kept  in  the  cooler  stables  from  the  start  nor  on  those  in 
warmer  quarters  when  the  temperature  of  the  latter  fell. 

Davis  l  reports  experiments  at  the  Pennsylvania  Station,  covering 
three  seasons,  in  which  comparable  lots  of  cows  were  kept  in  an  open 
shed  and  in  an  ordinary  "bank"  barn.  It  was  found  that  the  milk 
yield  of  both  was  similarly  affected  by  sudden  drops  of  temperature 
but  that  the  milk  yield  of  the  exposed  group  decreased  more  rapidly 
during  the  winter  than  did  that  of  the  sheltered  group,  the  difference 
in  the  average  daily  yield  for  the  entire  season  varying  from  practi- 
cally nothing  in  1911-1912  to  about  three  pounds  in  1913-1914.  It  was 
observed  that  the  exposed  cows  had  the  keener  appetites  and  con- 
sumed more  roughage  than  did  the  sheltered  animals.  Both  groups 
maintained  good  health.  The  amounts  of  milk  produced  per  Therm 
of  estimated  net  energy  contained  in  the  feed  and  also  per  Therm  of 
net  energy  in  excess  of  the  estimated  maintenance  requirement  were 
as  shown  in  the  following  table  from  which  it  appears  that  the  pro- 
duction by  the  sheltered  lot  was  slightly  the  more  economical. 

TABLE  129.  —  MILK  YIELDS  OF  SHELTERED  AND  EXPOSED  Cows 


PER  THERM 
NET  ENERGY 
OF  TOTAL 
FEED 

PER  THERM 
NET  ENERGY 
IN  EXCESS 
OF  MAINTE- 
NANCE 

Exposed  lot 

IQII—  12        

Lb. 
1.266 

Lb. 

2.24.4. 

IQI2—  12 

I  683 

2  ^7O 

IQI3—I4. 

I  4.^8 

2   CIC 

Average  . 

I  4.60 

2  44.3 

Sheltered  lot 
1911-12     

I.  31:4 

2.4QQ 

IQI2—  13 

I  737 

2  825 

1913-14        

I.4O2 

2.639 

Average  ....               

I  4.Q8 

2  6<?4. 

A  number  of  instances  have  also  been  reported  in  which  the  sub- 
stitution of  a  single  thickness  of  muslin  in  cow  stables  in  place  of 
glass  windows  has  proved  satisfactory. 

1  Penna.  Expt.  Sta.,  Rpt.  1913-1914,  pp.  183-226. 


488  NUTRITION  OF  FARM  ANIMALS 

On  the  whole  it  may  be  said  that  such  experiments  as  are  on 
record  agree  with  the  deductions  from  physiological  data  and 
indicate  that  the  need  for  warm  quarters  for  dairy  cows  has 
been  overemphasized,  but  are  insufficient  to  establish  the 
limits  within  which  stable  temperature  does  not  affect  yield. 
Much  doubtless  depends,  as  Spier  points  out,  upon  the  previous 
treatment  of  the  cows.  Warmly  stabled  animals  carry  a  sum- 
mer rather  than  a  winter  coat  and  a  low  temperature  seems 
likely  to  have  more  effect  on  such  animals  than  on  those  grad- 
ually accustomed  to  it  as  the  weather  grows  colder. 

Where  cows  are  kept  in  the  stable  most  of  the  time  the  ques- 
tion of  temperature  is  of  special  interest  in  its  relation  to  ventila- 
tion. Practically,  a  cow  stable  must  be  warmed  in  most  cases 
simply  by  the  heat  derived  from  the  animals  themselves  and 
a  high  temperature  can  be  obtained  only  by  means  of  more  or 
less  restricted  ventilation.  If  low  temperatures  can  be  used, 
more  perfect  ventilation,  with  its  beneficial  effects  upon  the 
health  and  vigor  of  the  animals,  is  possible. 

§  4.   THE  UTILIZATION  OF  FEED  IN  MILK  PRODUCTION 
The  utilization  of  protein 

584.  Meaning  of  utilization.  —  The  conception  of  the  utiliza- 
tion of  protein  in  milk  production  as  here  considered  is  substan- 
tially identical  with  that  of  its  utilization  in  growth  already 
discussed  (470).     It  is  the  ratio  of   the  protein  contained  in 
the  milk  to  the  least  amount  of  feed  protein  which  is  required 
to  produce  it  under  the  most  favorable  conditions. 

585.  Surplus  protein  katabolized.  —  While  it  is  evident  that 
milk  production  requires  a  liberal  supply  of  protein  in  the  ration, 
the  amount  actually  secreted  in  the  milk  is  determined  pri- 
marily by  the  individuality  of  the  animal,  precisely  as  is  the 
storage  of  protein  in  the  case  of  the  growing  animal.     It  is  not 
possible  to  increase  at  will  the  amount  of  protein  secreted  in 
the  form  of  milk  by  increasing  the  supply  of  protein  in  the  feed. 
While  it  appears  to  be  true  that  the  activity  of  the  milk  glands 
can  be  stimulated  somewhat  by  an  abundant  protein  supply 
(599) ,  it  is  nevertheless  true  that  the  animal  produces  an  amount 
of  milk  determined  essentially  by  its  capacity  and  any  surplus 
of  protein  over  that  necessary  for  this  purpose  is  katabolized 


MILK  PRODUCTION 


489 


just  as  is  the  case  with  a  surplus  supplied  to  a  young  animal,  or 
for  that  matter  to  a  mature  animal.  Feed  protein  is  substan- 
tially a  supply  of  material  and  not  a  cause  of  production. 

This  is  strikingly  illustrated  in  experiments  by  Jordan  1  in  which 
the  protein  supply  of  two  cows,  beginning  with  a  liberal  amount,  was 
gradually  diminished  to  about  one-half  and  then  gradually  increased 
again  to  the  original  quantity.  The  following  table  shows  the  aver- 
age nitrogen  balances  of  Cow  No.  12  of  the  second  series  of  experi- 
ments, the  daily  results  being  grouped  into  periods  as  indicated. 

TABLE  130.  —  AVERAGE  DAILY  NITROGEN  BALANCE  OF  Cows 


No.  OF 
DAYS 

NITROGEN 
DIGESTED 

NITROGEN 
OF  MILK 

NITROGEN 
OF  URINE 

GAIN  BY 
BODY 

Jan.  3o-Feb.  6      ... 

7 

Grams 
186.6 

Grams 
81.7 

Grams 
87.0 

Grams 
+  17-9 

Feb.  6-Feb.  16     ... 

10 

185.2 

81.4 

87.5 

+  16.3 

Feb.  i6-Feb.  26    ... 

10 

161.6 

77-5 

81.9 

+      2.2 

Feb.  26-Mar.  8    ... 

10 

130.8 

74.0 

56.5 

+  '    0.3 

Mar.  8-Mar.  18    .     .     . 

IO 

117.2 

66.6 

43-7 

+     6.9 

Mar.  i8-Mar.  28  ... 

IO 

143.6 

69.6 

61.8 

+  12.2 

Mar.  2  8-  Apr.  7     ... 

10 

171.4 

71.6 

89.2 

+  10.6 

Apr.  y-Apr.  14     ... 

7 

185-7 

71.9 

104.4 

+    9-4 

The  yields  decreased  in  quite  a  normal  way  with  the  advance  in 
lactation,  the  yield  of  protein,  like  that  of  total  milk  solids,  diminish- 
ing, while  the  percentage  of  protein  in  the  latter  remained  about  the 
same.  On  the  low  protein  rations  of  the  middle  periods  there  seems 
to  have  been  some  falling  off  in  the  amount  of  milk  protein  produced 
in  comparison  with  what  might  have  been  expected  on  an  unchanged 
ration,  but  the  difference  is  small  except  in  one  or  two  periods  in  which 
the  protein  supply  reached  the  lowest  limit.  Aside  from  this,  the 
principal  effect  of  the  variations  in  the  amount  of  digestible  protein 
supplied  was  to  increase  or  diminish  the  amount  of  nitrogen  excreted 
in  the  urine,  which,  as  the  table  clearly  shows,  rose  and  fell  with  the 
supply  of  nitrogen  in  the  food. 

586.  Estimates  of  utilization  of  protein.  —  In  attempting 
to  reach  conclusions  regarding  the  utilization  of  feed  protein 
for  the  production  of  milk  protein,  then,  it  is  evidently  necessary 
to  avoid  an  excess  of  protein  in  the  ration,  since  such  an  excess 

»N.  Y.  (Geneva)  Expt.  Sta.,  Buls.  132  (1897)  and  197  (1901). 


4QO  NUTRITION  OF  FARM  ANIMALS 

is  subject  to  rapid  katabolism,  so  that  high  protein  rations  will 
necessarily  show  a  low  apparent  utilization  of  the  protein  for 
milk  just  as  they  do  for  growth  (468) .  On  the  other  hand,  too 
small  a  supply  of  protein  may  cause  the  tissue  proteins  of  the 
body  to  be  mobilized  and  utilized  as  a  source  of  milk  protein  so 
that  a  direct  comparison  of  feed  protein  and  milk  protein  would 
give  too  high  a  result.  To  determine  the  utilization  of  feed 
protein,  therefore,  it  is  necessary,  while  maintaining  a  sufficient 
energy  supply,  to  reduce  the  protein  content  of  the  ration 
as  nearly  as  possible  to  that  which  is  just  sufficient  to  prevent 
a  loss  of  body  protein  and  then  to  compare  the  feed  protein 
minus  the  maintenance 'requirement  with  the  milk  protein. 

Such  an  experiment  obviously  requires  a  determination  of 
the  nitrogen  balance  of  the  animal,  and  relatively  few  of  the 
reported  investigations  on  milk  production  include  such  a 
determination,  while  in  none  yet  reported  has  the  sufficiency 
of  the  energy  supply  been  demonstrated  by  means  of  respira- 
tion experiments.  There  are,  however,  a  not  inconsiderable 
number  of  experiments  on  record  in  which  the  live  weights  of 
the  animals  have  been  well  maintained  and  in  which  amounts 
of  digestible  protein  but  little  greater  than  those  found  in  the 
milk  plus  those  estimated  to  be  necessary  for  maintenance  have 
been  adequate  for  the  production  of  at  least  moderate  amounts 
of  milk  without  drawing  on  the  body  protein. 

Naturally  an  exact  balance  of  the  income  and  outgo  of  nitrogen 
will  rarely  be  secured.  In  most  cases  it  is  necessary  to  compare  the 
feed  protein  with  the  algebraic  sum  of  the  milk  protein  and  the  gain 
or  loss  of  body  protein,  the  comparison  being  more  nearly  correct  as 
the  latter  factor  becomes  smaller. 

Table  131  shows  the  computed  utilization  of  the  protein 
of  a  number  of  low  protein  rations,  the  daily  maintenance 
requirement  of  crude  protein  being  estimated  as  0.6  pound  per 
1000  pounds  live  weight  in  direct  proportion  to  the  latter.  It 
includes  the  experiments  by  Jordan  upon  the  sources  of  milk 
fat,  the  results  of  one  of  which  as  regards  protein  have  just  been 
cited,  an  experiment  by  Hayward  1  the  results  of  which  as 
regards  the  nitrogen  balance  are  still  unpublished,  the  ex- 
tensive experiments  upon  the  minimum  protein  requirements 

1  Penna.  Expt.  Sta.,  Rpt.  1901-1902,  pp.  314  to  396. 


MILK  PRODUCTION 


491 


TABLE  131.  —  UTILIZATION  OF  PROTEIN  IN  MILK  PRODUCTION 


PE- 
RIOD 

NITRO- 
GEN DI- 
GESTED 

Grams 

ESTI- 
MATE 

FOR 

MAIN- 
TE- 
NANCE 

Grams 

RE- 
MAINS 

FOR 

PRO- 
DUC- 
TION 

Grams 

NITROGEN  UTILIZED 

PER- 
CENT- 
AGE 
UTIL- 
IZA- 
TION 

In 

Milk 

Grams 

In 

Body 
Gain 

Grams 

Total 

Grams 

Jordan 

Experiments  of  1897 

4 

65-5 

37-9 

27.6 

35-6 

-  3-5 

32.1 

116 

Experiments  of  1901 

5 

117.2 

52.3 

64.9 

66.6 

6.9 

73-5 

"3 

Hayward 

Cow  Cena    .     .     . 

3 

68.8 

36.8 

32.0 

33-7 

—     2.1 

31.6 

99 

Copenhagen       Lab- 

oratory 

4 

82 

32 

50 

63 

-  16 

47 

94 

Cow  10    ... 

5 

80 

32 

48 

60 

—  12 

48 

100 

6 

96 

32 

64 

62 

—      2 

60 

94 

Cow  23     ... 

4 
5 

81 
83 

35 
35 

46 
48 

59 

57 

-    9 

-  15 

50 
42 

109 
87 

4 

87 

30 

57 

56 

—      2 

54 

95 

Cow  53     ... 

5 

67 

3° 

37 

45 

-  13 

32 

86 

6 

Qi 

30 

61 

49 

+    3 

52 

85 

4 

92 

32 

60 

63 

-    5 

58 

97 

Cow  68     ...      . 

5 

80 

32 

48 

58 

-  16 

42 

88 

H 

81 

32 

49 

So 

—      2 

48 

98 

f 

4 

85 

32 

53 

52 

—      I 

5i 

96 

Cow  58    ... 

5 

64 

32 

32 

45 

-13 

32 

100 

1 

6 

93 

32 

61 

47 

+    6 

53 

87 

3 

92 

30 

62 

65 

-  16 

49 

79 

Cow  68    ... 

4 

5 

68 
66 

3° 
30 

38 
36 

59 
58 

-  26 
-  23 

33 
35 

87 
97 

6 

92 

3° 

62 

59 

-    4 

55 

87 

4 

124 

33 

9i 

83 

-  17 

66 

73 

Cow  125  ... 

5 
6 

123 
142 

33 
33 

90 
109 

83 
79 

-  12 

+    4 

7i 
83 

79 
76 

7 

148 

33 

H5 

79 

+    7 

86 

75 

Kellner 

Cow  E      .     .     .      { 

4 

96 

35 

61 

57 

+    i 

58 

95 

5 

99 

35 

64 

61 

+    i 

62 

97 

492  NUTRITION  OF  FARM  ANIMALS 

of  dairy  cows  carried  on  at  the  Laboratory  for  Agricultural 
Research  in  Copenhagen  1  and  unpublished  respiration  experi- 
ments by  Kellner.2  The  experiments  of  Hart  and  Humphrey 
mentioned  in  the  next  paragraph,  when  computed  in  the  same 
way,  also  show  a  high  percentage  utilization  of  the  digested 
protein,  although  the  gains  and  losses  of  body  protein  are 
relatively  so  considerable  as  to  disturb  the  comparison. 
Haecker's  low  protein  rations  in  1902-3-4-5,  as  noted  on  a 
subsequent  page  (602),  seem  to  afford  another  example  of  the 
high  utilization  of  feed  protein. 

While  too  much  weight  should  not  be  attached  to  the  results 
of  comparisons  like  the  foregoing,  especially  since  they  include 
a  more  or  less  uncertain  estimate  of  the  protein  requirement 
for  maintenance,  they  nevertheless  seem  to  indicate  beyond 
reasonable  doubt  that  on  low  protein  rations  the  protein  of  at 
least  some  feeding  stuffs  may  be  converted  into  milk  protein 
without  any  very  large  loss. 

587.  Relative  values  of  proteins  for  milk  production.  —  The 
considerations  advanced  in  preceding  chapters  (400,  465)  regard- 
ing the  relative  values  of  different  proteins  for  maintenance  and 
for  production  render  it  altogether  probable  that  they  also  differ 
in  value  as  sources  of  milk  protein.  No  experiments  on  this 
point  have  as  yet  been  reported,  but  Hart  and  Humphrey 3  in 
two  series  of  experiments  on  cows  have  compared  the  mixed 
proteins  of  maize,  wheat,  gluten  feed,  oil  meal  and  distillers' 
grains  with  proteins  prepared  from  milk  (784),  using  maize 
stover  and  silage  as  roughage.  They  found  the  average  per- 
centage of  the  resorbed  nitrogen  which  was  recovered  in  the 
milk  yield  plus  the  gain  (or  minus  the  loss)  of  the  body  protein 
to  be 

Skim  milk  powder 59  % 

Casein 59% 

Maize 40% 

Wheat 36% 

Gluten  feed 45  % 

Oil  meal 61  % 

Distillers'  grains 60% 

1  Denmark-Beretning  fra  den  Kgl.  Veterinea-r  of  Landbohojskoles  Laboratorium 
for  landokonomiske  Forsog.     6ode,  1906,  and  63de,  1907,  Kobenhavn.     Translated 
by  Mallevre,  Societe  de  1'Alimentation  Rationale  du  Betail.     Compte  Rendu  de 
ueme  et  i2eme  Congres. 

2  Die  Ernahrung  der  landw.  Nutztiere,  6th  Ed.,  1912,  p.  551. 

3  Jour.  Biol.  Chem.,  21  (1915),  239;   26  (1916),  457. 


MILK  PRODUCTION  493 

If  the  probable  requirement  for  protein  maintenance  be 
deducted  from  the  total  resorbed  nitrogen,  the  utilization  of 
the  remaining  protein,  calculated  as  in  the  experiments  of  the 
previous  paragraph,  was  notably  higher,  approaching  or  reach- 
ing 100  per  cent  in  several  instances. 

The  differences  observed  were  largely  due,  however,  to  fluc- 
tuations in  the  gain  or  loss  of  body  protein,  the  formation  of 
milk  protein  being  quite  uniform  from  period  to  period,  and 
this  fact  seems  to  render  the  results  of  somewhat  questionable 
relevance  as  regards  the  special  question  of  comparative  values 
as  sources  of  milk  protein,  although  they  do  show  marked 
differences  in  total  efficiency. 


The  utilization  of  energy 

588.  Net   energy   values   for   milk   production.  —  The   net 

energy  value  of  a  feeding  stuff  or  ration  for  milk  production  is 
identical  in  conception  with  that  for  fattening  (448)  or  for 
growth  (472)  already  considered.  It  is  that  part  of  the  feed 
energy  supplied  in  excess  of  the  maintenance  requirement  which 
is  recovered  in  the  product.  For  example,  if  a  cow  produces 
per  day  20  Ib.  of  four  per  cent  milk,  Containing  (604)  336 
Cals.  of  energy  per  pound,  the  total  of  6720  Cals.  would  be  the 
net  energy  value  which  must  be  supplied  in  the  ration  in  ad- 
dition to  that  required  for  maintenance. 

As  pointed  out  in  Chapter  VIII  (371),  it  cannot  be  assumed 
that  the  net  energy  values  for  maintenance,  fattening  or  growth 
apply  to  milk  production,  but  the  values  for  the  latter  purpose 
must  be  determined  by  direct  experiment.  As  yet,  very  scanty 
data  are  available  on  this  point,  the  only  results  yet  reported 
being  three  contained  in  a  brief  preliminary  paper  by  Kellner. 

589.  Complete    energy    balances.  —  Kellner 1    reports    the 
nitrogen,  carbon  and  energy  balances,  determined  as  in  his  ex- 
periments on  oxen,  of  three  cows  receiving  mixed  rations  and 
varying  considerably  in  their  milk  yield.     By  the  method  de- 
scribed in  Chapter  XVII  (768-772),  it  is  estimated  that  the  net 
energy  values  of  the  rations  and  the  percentage  utilization  of 
their  metabolizable  energy  for  fattening  would  be :  — 

1  ster  Internal.  Kongress  fur  Milchwirtschaf t,  191 1 . 


494 


NUTRITION  OF  FARM   ANIMALS 


STARCH 
VALUES 

EQUIVALENT 
NET  ENERGY  1 

NET  ENERGY 
AS  PERCENTAGE 
OF  METABOLIZ- 
ABLE  ENERGY 

Cow  A    ... 

Kgs. 
6  96 

Therms 

% 

Cow  C    . 

6  12. 

I  A.  A.A.1. 

d.6  3  s 

Cow  E 

A  SA 

AT.  8l 

Estimating  the  maintenance  requirements  of  the  animals 
from  their  live  weights  on  the  basis  of  his  average  results  on 
the  maintenance  of  oxen  (381),  Kellner  obtains  the  following 
energy  balances  showing  a  considerably  higher  utilization  for 
milk  production  than  that  computed  for  fattening. 

TABLE  132.  —  ENERGY  BALANCES  OF  DAIRY  Cows 


Cow  A 

Cow  C 

Cow  E 

Therms 

Therms 

Therms 

Income 

In  feed      .     .     .     . 

63.309 

59.096 

46.536 

Outgo 

In  feces  and  urine  . 

25.353 

23.783 

16.996 

In  methane   .     .     . 

3-803 

4.149 

3.508 

Total     .... 

29.156 

27.932 

20.504 

Metabolizable 

Total    .          ... 

-24.  I  C7 

31.164 

26.032 

Estimated   mainte- 

O'*' AOO 

O      *  t-^JLT 

nance     .     .     . 

10.114 

H.303 

10.586 

Available   for   pro- 

duction .     .     . 

24.039 

I9.86I 

15.446 

Production 

Milk     

13.007 

IO.6l7 

8.919 

Body     fat     and 

o  y    / 

protein  .     .     . 

1.782 

2.447 

0.928 

Total     .... 

15.689 

13.064 

9.847 

Utilization  of  metab- 

% 

% 

% 

olizable  energy  .     . 

65-3 

65.8 

63.8 

Computed  utilization 

for  fattening       .     . 

48.0 

46.4 

43-8 

li  Kilogram  starch  value  =  2.356  Therms  net  energy. 


MILK  PRODUCTION 


495 


The  percentage  utilization  in  milk  production  alone  may  also 
be  approximately  estimated  from  Kellner's  figures  by  sub- 
tracting from  the  metabolizable  energy  available  for  production 
the  amounts  estimated  to  be  required  for  the  production  of  the 
observed  gain  of  body  tissue.  The  results  of  this  calculation 
are  shown  in  the  following  table.  A  similar  computation  by 
Kellner  based  on  his  estimated  starch  values  gives  substantially 
the  same  results. 

TABLE  133.  —  UTILIZATION  OF  METABOLIZABLE  ENERGY  IN  MILK  PRO- 
DUCTION 


Cow  A 

Cow  C 

Cow  E 

Metabolizable  energy 
Available  for  total 
production     .     . 
Required  for  body  gain 
Available  for  milk 
production     .     . 
Recovered  in  milk  . 
Utilization     .     .     . 

24.039  Therms 
3:711       " 

19.861  Therms 
5-279      „ 

15^446  Therms 
2.118      " 

13-328      " 
8.919      " 
66.91% 

20.328      " 
13.907 
68.41'% 

14-582      " 
10.617      " 
72.80% 

590.  Partial  energy  balances.  —  Partial  energy  balances  of 
two  cows  which  made  but  slight  gains  in  live  weight  are  re- 
ported by  Jordan,1  the  maintenance  requirement  being  esti- 
mated from  the  live  weight  and  the  excretion  of  methane  com- 
puted from  the  digestible  carbohydrates.  Assuming  that  there 
was  no  gain  or  loss  of  fat  or  protein  by  the  body,  the  following 
comparisons  can  be  made :  — 

TABLE  134.  —  UTILIZATION  OF  METABOLIZABLE  ENERGY  IN  MILK  PRO- 
DUCTION 


COW   12 

Period  i 

Period  2 

Period  3 

Metabolizable  energy  .  . 
Estimated  maintenance  . 

27.320  Therms 
10.152 

32.118  Therms 
13-846     " 

31.718  Therms 
13-846     ' 

30.335  Therms 
13-846     ' 

Energy  in  milk  .... 
Utilization  

17.168     " 
8-4SI     ' 
49-23% 

18.272     " 
11.176     " 
61.16% 

17.872     " 
10.169     ' 
56.90% 

16.489     " 
10.547     ' 
63.96% 

1  N.  Y.  (Geneva)  Expt.  Sta.,  Bui.  197,  pp.  24-32  and  2oth  Rpt.  (1901),  p.  29. 


496  NUTRITION  OF  FARM  ANIMALS 

Eckles  1  has  likewise  determined  partial  energy  balances  of 
ten  milking  cows  for  an  entire  year  on  rations  just  sufficient  to 
maintain  their  live  weight.  In  these  experiments  the  percentage 
digestibility  of  the  rations  is  computed  for  eight  of  the  cows  on 
the  basis  of  results  obtained  in  digestion  trials  on  five  of  the 
animals,  while  the  maintenance  requirement  of  all  but  one  of  the 
cows  was  determined  in  live  weight  experiments  after  the  cows 
were  dried  off,  with  the  results  reported  in  Chapter  VIII  (381). 

Estimating  the  metabolizable  energy  of  the  rations  at  3.7 
Therms  per  kilogram  of  digestible  organic  matter  (753)  and  com- 
puting the  results,  exactly  as  in  Jordan's  experiments,  on  the 
assumption  of  no  gain  or  loss  by  the  body,  the  following  values, 
for  the  percentage  utilization  in  milk  production  are  obtained. 

TABLE  135.  —  PERCENTAGE  UTILIZATION  OF  METABOLIZABLE  ENERGY  IN 
MILK  PRODUCTION 

Cow  No.  206 63.36  % 

Cow  No.  304 67.60% 

Cow  No.  400 66.90  % 

Cow  No.  43 5I-36% 

Cow  No.  62 72.82% 

Cow  No.  4 60.24% 

Cow  No.  27 62.89% 

Cow  No.  63 50.35  % 

Average 61.94% 

Haecker,2  in  discussing  the  results  of  extensive  experiments 
with  the  dairy  herd  of  the  Minnesota  Experiment  Station,  has 
compared  the  digestible  nutrients  of  the  feed  and  the  solids  of 
the  milk  by  reducing  both  to  their  carbohydrate  equivalent.3 
Subtracting  the  estimated  maintenance  requirement  from  the 
total  carbohydrate  equivalent  ("  nutriment  ")  of  the  feed,  he 
finds  that  of  the  remainder  from  50.25  per  cent  to  66.22  per 
cent  was  recovered  in  the  milk,  the  general  average  for  nine 
years  being  54.65  per  cent,  while  the  live  weights  of  the  cows 
were  in  general  maintained.  This  seems  to  indicate  a  decidedly 
lower  utilization  of  energy  than  that  computed  in  Kellner's, 
Jordan's  and  Eckles'  experiments.  It  must  be  noted,  however, 

1  Mo.  Expt.  Sta.,  Research  Bui.  7. 

2  Minn.  Expt.  Sta.,  Bui.  140  (1914),  p.  45. 

3  The  fat  of  the  feed  is  multiplied  by  the  factor  2.2  and  that  of  the  milk  by  2.25 
and  the  product  added  to  the  carbohydrates  and  protein.     The  sums,  which  are 
called  "  nutriment,"  are,  of  course,  approximately  proportional  to  the  energy  con- 
tent of  the  milk  and  the  metabolizable  energy  of  the  feed  respectively. 


MILK  PRODUCTION  497 

that  the  digestibility  of  the  rations  in  Haecker's  experiments 
was  estimated  from  average  figures  which,  according  to  Eckles' 
results  (722),  are  probably  too  high  for  cows  in  milk,  although 
on  the  other  hand  Haecker's  estimate  for  the  maintenance  re- 
quirement also  seems  high. 

591.  Net  energy  values  for  milk  probably  greater  than  for 
fattening.  —  A  comparison  of  Kellner's  results  (589)  with  those 
obtained  by  the  same  author  1  and  by  Armsby  and  Fries  2  for 
the  utilization  of  metabolizable  energy  in  either  maintenance, 
growth  or  fattening   seems   to  indicate   clearly  that   the  net 
energy  values  for  milk  production  are  distinctly  higher  than 
those  for  the  latter  purposes,  although  no  direct  comparisons 
on  the  same  feeding  stuff  or  ration  can  be  made. 

Both  Jordan's  and  Eckles'  results  tend  to  confirm  this  con- 
clusion, which  is  further  strengthened  by  the  fact,  to  which 
Eckles  calls  attention,  that  with  one  exception  the  actual  energy 
content  of  the  milk  in  his  experiments  was  greater  than  the  net 
energy  value  available  in  the  ration  producing  it  as  computed 
by  the  use  of  Kellner's  factors. 

Unfortunately,  no  results  upon  the  net  energy  values  of 
single  feeding  stuffs  or  nutrients  for  milk  production  have  yet 
been  reported,  so  that  it  is  impossible  at  present  to  make  any 
exact  quantitative  comparisons. 

592.  Cause  of  higher  net  energy  values  for  milk  production. 
—  The  apparently  higher  net  energy  values  for  milk  produc- 
tion as  compared  with  tissue  production  may  be  plausibly  as- 
cribed to  the  difference  in  the  composition  of  the  products. 
As  shown  in  Chapters  X  and  XI,  the  organic  matter  of  the  in- 
crease in  fattening  consists  chiefly  of  fat  (441-443)  and  even  in 
the  case  of  growth  fat  makes  up  a  considerable  proportion  of  it 
(458)  except  in  extreme  youth.     In  average  milk,  on  the  com- 
trary,  protein  and  milk  sugar  constitute  two-thirds  of  the  total 
organic  matter  and  carry  over  one-half  of  the  total  energy. 

It  seems  not  improbable  that  the  conversion  of  digestible 
protein  into  milk  protein,  or  of  digestible  carbohydrates  into 
milk  sugar,  may  involve  a  comparatively  small  expenditure 
of  energy  as  compared  with  the  synthesis  of  fat  from  carbo- 
hydrates or  protein.  If  such  be  the  case,  the  organic  matter 

1  Landw.  Vers.  Sta.,  53  (1900),  i. 

2  Jour.  Agr.  Research,  3  (1915),  435;  7  (1916),  379. 


498 


NUTRITION  OF  FARM   ANIMALS 


of  the  milk  would  retain  a  larger  percentage  of  the  chemical 
energy  of  the  digestible  matter  from  which  it  was  formed  than 
would  the  increase  of  body  tissue  which  that  same  digestible 
matter  could  produce. 

593.  Computation  of  equivalent  net  energy  values  for  fat- 
tening. —  Let  it  be  assumed  that  the  digestible  protein  and 
carbohydrates  of  the  feed  may  be  converted  into  the  corre- 
sponding compounds  of  milk  without  loss  and  that  the  expendi- 
ture of  energy  in  the  production  of  milk  fat  from  carbohydrates 
is  the  same  as  that  observed  by  Kellner  (769)  for  the  production 
of  body  fat.  Then  each  gram  of  protein  or  carbohydrates  in 
the  milk  would  require  the  supply  in  the  feed  of  one  gram  of 
digestible  protein  or  carbohydrates  respectively,  while  each 
gram  of  milk  fat  if  manufactured  from  carbohydrates  would 
require  about  3.9  grams  of  the  latter. 

The  corresponding  amounts  of  energy  recovered  in  milk 
production  and  in  fattening  respectively  would,  according  to 
the  foregoing  assumptions,  be  as  follows :  — 

TABLE  136.  —  COMPUTED  ENERGY  RECOVERED  IN  MILK  PRODUCTION  AND 
IN  FATTENING 


SUPPLIED  IN  FEED 

PRODUCED  IN  MILK 

ENERGY 
RECOVERED 
IN  MILK 

ENERGY 
RECOVERED 
IN  FATTEN- 
ING l 

i     gram  protein 
i     gram  carbohydrates 
3.9  grams  carbohydrates 

i  gram  protein 
i  gram  carbohydrates 
i  gram  fat 

5.7    Cals. 
4.1    Cals. 
9.23  Cals. 

2.24  Cals. 
2.37  Cals. 
9.23  Cals. 

On  this  basis,  it  is  easy  to  compute  approximately  the  amount 
of  net  energy  for  fattening  which  would  be  required  for  the 
production  of  a  given  amount  of  milk  of  known  composition. 
Thus  average  four  per  cent  milk,  according  to  Table  144  (604), 
contains  3.08  per  cent  of  protein,  4.85  per  cent  of  carbohy- 
drates and  4.0  per  cent  of  fat.  The  actual  amount  of  energy 
contained  in  a  pound  of  such  milk  would  be  336  Cals.,  while 
the  amount  of  energy  which  would  have  been  recovered  from 
the  same  feed  if  used  for  fattening  would  have  been  only  252 
Cals.  Conversely,  an  amount  of  feed  containing  252  Cals.  of 
net  energy  as  computed  from  the  results  of  fattening  experi- 

1  Kellner's  factors. 


MILK  PRODUCTION 


499 


ments  would  suffice  to  support  the  storage  of  336  Cals.  of 
energy  in  four  per  cent  milk.  The  method  of  computation  is 
shown  in  the  following  table. 

TABLE   137.  —  ENERGY  RECOVERED  IN  FOUR  PER  CENT  MILK  AND  IN 

FATTENING 


ENERGY  RECOVERED  IN 
MILK 

EQUIVALENT  ENERGY  RE- 
COVERED IN  FATTENING 

Protein     .... 
Carbohydrates  .     . 
Fat                ... 

5.7     X  3.08  =  17.5  Cals. 
4.1     X  4.85  =  19.8  Cals. 
9.23  X  4.00  =  36.9  Cals. 

2.24  X  3.08  =    6.9  Cals. 
2.37  X  4-85  =  1  1.5  Cals. 
0.23  X  4.00  =  36.0  Cals. 

Total  per  100  grams 
Total  per  pound     . 

74.2  Cals. 
336     Cals. 

5^3  Cals. 
252     Cals. 

594.  Kellner's  results.  —  Confirmation  of  this  hypothesis 
is  afforded  by  the  results  of  Kellner's  respiration  experiments 
(589).  In  substantially  the  way  just  outlined,  Kellner  com- 
putes that  while  the  actual  chemical  energy  of  the  milk  solids  pro- 
duced by  his  cow  A  was  13.907  Therms,  this  was  equivalent  to 
only  10.367  Therms  of  net  energy  value  for  fattening,  and  there- 
fore, that  a  ration  supplying  this  amount  in  excess  of  that  re- 
quired for  maintenance  and  body  gain  should  be  sufficient  to 
support  the  observed  milk  production.  For  the  three  cows  for 
which  results  are  reported,  the  requirements  for  net  energy  as 
thus  computed  compared  with  the  estimated  net  energy  values 
of  the  rations  were  as  follows :  — 


TABLE  138. 


NET  ENERGY  VALUES  FOR  FATTENING  IN  KELLNER'S  EX- 
PERIMENTS 


Cow  A 

Cow  C 

Cow  E 

Total  in  ration 

Therms 
1  6  400 

Therms 
I  A  4.4.3 

Therms 

1  1  4.O  3 

Required  for  maintenance 

4.  ^04 

c  137 

4806 

Required  for  body  gain  

1  1.  806 

1.782 

9.306 
2.447 

6-597 
.928 

Available  for  milk  production       .... 
Computed  requirement  for  milk  produc- 
tion 

10.024 
10  367 

6.859 
6  O7  ? 

5-669 

6  O7O 

500  NUTRITION  OF   FARM   ANIMALS 

The  amounts  of  net  energy  actually  available  for  milk  pro- 
duction correspond  quite  closely  with  the  amounts  computed 
to  be  required  according  to  the  foregoing  assumptions,  and 
Kellner  states  that  this  was  also  the  case  in  a  considerable 
number  of  his  unpublished  experiments,  although  in  others, 
especially  those  in  which  a  surplus  of  feed  was  given,  the  agree- 
ment was  far  from  being  so  good,  the  difference  in  one  case 
reaching  24  per  cent. 

Quite  in  harmony  with  the  general  conclusions  of  the  fore- 
going paragraphs  is  the  statement  by  Eckles  1  that  in  his  ex- 
periments "  A  therm  of  energy  in  the  feed  produced  more  energy 
in  milk  when  the  per  cent  of  fat  was  low  than  when  it  was  high. 
Apparently  a  given  amount  of  feed  is  more  efficient  when  used 
to  produce  milk  medium  to  low  in  fat.  It  appears  from  this 
that  the  production  of  fat  is  a  greater  tax  upon  the  animal  than 
is  the  production  of  other  constituents  of  the  milk  carrying 
equal  energy  value." 

§  5.  FEEDING  FOR  MILK  PRODUCTION 

595.  Feeding  a  secondary  factor.  —  As  has  already  been 
urged,  the  feeding  of  a  milking  animal  is  in  a  certain  sense  a 
secondary  factor  in  dairying.  The  possibilities  of  successful 
milk  production  depend  primarily  upon  the  capacity  of  the 
animals  as  milk  producers  and  upon  the  maintenance  of  such 
an  environment  as  will  give  free  play  to  this  capacity.  Feed, 
on  the  other  hand,  while  equally  necessary, »is  after  all  essentially 
the  supply  of  raw  material  upon  which  the  animal  mechanism 
works  and  cannot  greatly  stimulate  production,  though  it  may 
limit  it  for  lack  of  material. 

The  same  thing  is  substantially  true,  of  course,  of  all  forms 
of  productive  feeding,  but  it  is  especially  the  case  in  the  feeding 
of  dairy  animals  for  the  reason  already  noted  (558),  that  it  is 
the  product  of  a  single  gland  and  not  a  general  increase  of  body 
tissue  which  is  desired.  Improper  rations,  therefore,  may  in 
this  case  not  only  limit  the  total  production  but,  even  if  suffi- 
cient in  quantity,  may  if  deficient  in  quality  deflect  production 
from  milk  to  fattening,  or  possibly  to  greater  muscular  activity, 
and  thus  fail  to  utilize  fully  the  milk-producing  capacity  of  the 

1  Loc.  dt.,  p.  137. 


MILK  PRODUCTION  501 

animals.     Feeding,   therefore,   while  in   a   sense   a   secondary 
factor  is  nevertheless  an  important  one. 

596.  Feed  requirements.  —  Regarded  solely  as  a  source  of 
material  for  the  formation  of  milk,  the  daily  ration  must,  of 
course,  contain  an  adequate  amount  of  protein  and  ash  and 
a  quantity  of  non-nitrogenous  nutrients   sufficient  to  furnish 
material  for  the  manufacture  of  the  non-nitrogenous  ingredi- 
ents of  the  milk,  while  it  must  also  supply  enough  energy  for 
the  physiological  activities  of  the  body,  including  maintenance 
and  the  energy  expended  in  the  processes  of  milk  formation. 

In  addition  to  this,  however,  there  must  be  taken  into  con- 
sideration the  possibility  of  the  presence  or  absence  in  the  feed 
of  substances  which  may  have  a  specific  effect  on  the  milk 
gland,  either  by  stimulating  or  depressing  its  action  as  a  whole 
or  by  affecting  qualitatively  the  character  of  its  action  and  so 
the  composition  of  the  milk.  There  is,  of  course,  a  possibility 
of  such  specific  effects  in  other  forms  of  production,  but  it  is 
most  obvious  in  milk  production  for  evident  reasons  and  has 
been  most  studied  in  that  connection. 

Protein  requirements  for  milk  production 

597.  Milk  rich  in  protein.  —  The  physiological  purpose  of 
milk  production  is,  of  course,  to  support  the  growth  of  the  young. 

The  essential  feature  of  growth,  however  (462),  is  the  pro- 
duction of  new  protein  tissue,  which,  in  the  suckling  animal, 
is  relatively  rapid,  and  in  order  to  support  this  growth  the  milk 
must  contain  protein  in  amount  more  or  less  proportional  to 
the  rate  of  growth  of  the  species.  Cow's  milk  is  decidedly 
protein  in  character,  the  ratio  of  protein  to  non-nitrogenous 
ingredients  corresponding  roughly  with  that  of  the  increase 
made  by  an  animal  three  months  old  (556) .  Moreover,  in  the 
case  of  the  cow,  man  has  been  able  to  increase  greatly  the  natural 
milk-producing  capacity,  with,  of  course,  a  corresponding  in- 
crease in  the  total  amount  of  milk  protein  formed.  Even  the 
moderate  daily  yield  of  20  pounds  of  milk  of  average  composi- 
tion contains  over  0.6  pound  of  protein,  while  the  extraordinary 
yields  of  champion  cows  contain  several  times  this  amount. 

598.  Minimum  protein  requirement.  —  Just  as  in  the  case  of 
growth,  it  is  evident  that  the  least  amount  of  digestible  protein 


502  NUTRITION  OF  FARM  ANIMALS 

which  can  possibly  meet  the  requirements  of  the  milk-producing 
animal  is  the  quantity  required  for  the  maintenance  of  the  body 
protein  plus  the  actual  amount  of  protein  contained  in  the  milk 
yielded.  For  example,  if  a  looo-pound  cow  is  to  produce  daily 
25  pounds  of  milk  containing  3.2  per  cent  of  total  protein, 
it  is  evident  that  her  ration  must  contain  in  digestible  form 
at  least  the  0.8  pound  of  protein  contained  in  the  milk  plus 
the  approximate  0.6  pound  presumably  required  for  body 
maintenance,  or  a  total  of  approximately  1.4  pounds.  A  less 
supply  than  this  must  evidently  result  either  in  a  falling 
off  in  the  milk  yield  or  in  a  conversion  of  body  protein  into 
milk  protein. 

How  much  more  than  this  minimum  amount  must  be  sup- 
plied by  an  adequate  ration  will  depend  upon  the  percentage 
utilization  of  the  feed  protein  in  the  sense  already  discussed  in 
§  4  of  this  chapter  (584-586),  i.e.,  upon  the  proportion  of  it 
capable  of  conversion  into  milk  protein.  Thus  in  the  illustra- 
tion just  employed,  if  80  per  cent  of  the  surplus  feed  protein 
can  be  utilized  the  protein  requirement  would  be  i  .o  pound  for 
milk  production  plus  0.6  pound  for  maintenance,  or  1.6  pound 
instead  of  1.4  pound.  The  case  is  parallel  with  that  of  the 
protein  requirement  for  growth  discussed  in  Chapter  XI  (484- 
491)  and  in  both  instances  the  experimental  data  available  are 
insufficient  for  a  final  conclusion,  although  the  probabilities 
appear  to  indicate  the  possibility  of  a  high  percentage  utilization 
under  favorable  conditions. 

599.  Protein  as  a  stimulus  to  the  milk  glands.  —  The  fore- 
going considerations  do  not,  however,  exhaust  the  subject.  In 
them  it  has  been  tacitly  assumed  that  the  amount  of  milk  protein 
manufactured  by  the  milk  glands  is  substantially  fixed.  It 
seems  well  established,  however,  that  in  addition  to  furnishing 
material  for  the  manufacture  of  milk  protein,  the  nitrogenous 
matter  of  the  feed  may  act  to  some  extent  as  a  stimulus  to  the 
glands,  causing  a  more  active  secretion  not  only  of  protein  but 
of  all  the  milk  solids.  In  other  words,  it  would  appear  that  a 
greater  or  less  surplus  of  protein  over  the  amount  indicated  by 
calculations  like  the  foregoing  is  necessary  if  it  is  desired  to  take 
full  advantage  of  the  milk-producing  capacity  of  the  animal  or 
to  delay  as  much  as  possible  the  natural  shrinkage  in  milk  due 
to  advancing  lactation. 


MILK  PRODUCTION  503 

That  such  is  the  case  has  long  been  taught,  but  many  of  the 
early  experiments  upon  which  this  teaching  was  based  are 
inconclusive  in  that  they  relate  to  the  effect  of  adding  protein- 
rich  feeding  stuffs  to  relatively  light  rations  low  in  protein.1 
The  total  digestible  matter  (energy  supply)  as  well  as  the  protein 
in  the  rations  was  thus  increased,  sometimes  by  a  considerable 
amount,  the  quality  of  the  protein  sometimes  improved, 
and  the  proportions  of  the  ash  ingredients  more  or  less  altered, 
while  the  possibility  of  the  presence  in  the  added  feed  of  specific 
stimulating  substances  (617-621)  must  be  reckoned  with.  It  is 
illogical,  therefore,  to  ascribe  the  beneficial  effect  entirely  to 
the  increase  in  digestible  protein,  although  this  was  doubtless 
one  of  the  factors. 

Jordan's  investigations.  —  Of  more  recent  investigations  in 
which  these  sources  of  uncertainty  were  largely  avoided  those 
of  Jordan,  some  of  the  results  of  which  as  regards  the  utilization 
of  protein  have  already  been  cited  (585),  afford  a  good  example 
and  may  serve  to  illustrate  the  general  method  of  such  experi- 
ments. Beginning  with  a  ration  fairly  high  in  protein,  the 
proportion  of  this  nutrient  was  gradually  reduced  to  a  com- 
paratively low  figure  and  then  gradually  increased  again  to  the 
original  amount  by  an  exchange  in  the  rations  between  a  nearly 
pure  protein  (wheat  gluten)  and  either  maize  or  rice  meal. 
The  total  digestible  matter  was  thus  kept  practically  constant 
while  the  probability  of  any  specific  effect  was  reduced  to  a 
minimum. 

The  actual  yields  of  total  milk  solids  and  of  milk  protein  in 
the  several  periods  are  recorded  in  Table  139  and  together 
afford  a  fairly  accurate  measure  of  the  amount  of  production. 
Before  drawing  conclusions  as  to  the  influence  of  the  varying 
protein  supply,  however,  it  is  necessary  to  take  account  of  the 
natural  shrinkage  in  milk.  Assuming  that  the  rate  of  falling 
off  in  milk  due  to  advancing  lactation,  as  shown  by  the  differ- 
ence between  the  first  and  last  periods,  was  uniform  (571), 
the  actual  yields  of  solids  and  of  protein  as  compared  with 
those  which  would  have  been  anticipated  had  the  feed  re- 
mained unchanged,  were  as  follows :  — 

1  Compare  Wolff's  summary  in  Ernahrung  der  landw.  Nutztiere,  1876,  pp.  500- 
550- 


504 


NUTRITION  OF  FARM   ANIMALS 


TABLE   139.  —  INFLUENCE  OF   PROTEIN   SUPPLY   ON  MILK  PRODUCTION 
(Results  per  day  and  head) 


CRUDE 

YIELD  OF  MILK 
SOLIDS 

YIELD  or  MILK 
PROTEIN 

GAIN 

PRO- 

OF 

PERIOD 

TEIN 

BODY 

DI- 

PRO- 

GESTED 

Com- 
puted 

Ob- 
served 

Com- 
puted 

Ob- 
served 

TEIN 

Lb. 

Lb. 

Lb. 

Lb. 

Lb. 

Lb. 

I 

1.70 

2.72 

2.72 

0.64 

0.64 

+  0.03 

2 

1.42 

2-59 

2.28 

0.62 

0.62 

+  0.05 

Experiment  of  1897 

.  3 

1.85 

2.49 

2.22 

0.60 

o-59 

+  0.40 

4 

0.90 

2.38 

1.87 

0.58 

0.49 

—  0.05 

5 

0.41 

2.24 

I-67 

0.56 

0.44 

-0.43 

6 

1.58 

1.96 

1.96 

0.51 

0.51 

+  0.46 

i 

2-57 

4-55 

4-55 

1.  12 

1.  12 

+  0.25 

2 

2.63 

4.41 

4.20 

I.IO 

1.  12 

+  0.30 

3 

2.  2O 

4.28 

4.02 

1.  08 

1.07 

o 

Experiment  of  1901     . 

4 
5 

1.  80 
1.  60 

4.14 
4.01 

3-77 
3-50 

1.  06 
1.05 

I.O2 
0.92 

o 

+  0.08 

6 

1.98 

3.87 

3-57 

1.03 

0.96 

+  0.17 

7 

2-35 

3-73 

3-65 

I.OI 

0.99 

+  0-13 

,8 

2-55 

3.60 

3-6o 

0.99 

0.99 

+  0.12 

Although  the  low  protein  rations  were  able  to  support  a  con- 
siderable milk  production  without  causing  the  body  protein  to 
be  drawn  upon  materially,  nevertheless,  a  more  liberal  supply 
of  digestible  protein  was  accompanied  by  a  distinctly  greater 
production  of  both  total  milk  solids  and  milk  protein. 

Morgen's  investigations.  —  The  extensive  investigations  of 
Morgen  and  his  associates  l  upon  milk  production  by  sheep 
include  a  large  number  of  trials  in  which  an  exchange  between 
comparatively  pure  protein  on  the  one  hand  and  starch  or  oil 
on  the  other  was  made  in  the  rations.  The  results,  therefore, 
afford  valuable  data  regarding  the  influence  of  the  protein 
supply  as  distinguished  from  the  possible  effects  of  associated 
factors.  In  nearly  all  instances  the  ration  of  the  low  protein 
period  contained  a  considerable  surplus  of  digestible  protein 
above  the  total  of  milk  protein  plus  maintenance  protein.  In 
the  following  table,  computed  by  the  writer,  the  experiments 

1  Landw.  Vers.  Stat.,  61  (1904),  i ;  62  (1905),  251 ;  64  (1906),  93 ;  66  (1907),  63. 


MILK  PRODUCTION 


505 


have  been  grouped  according  to  the  amount  of  this  surplus,  and 
the  average  percentage  increase  in  the  yield  of  milk  solids  and 
of  milk  fat  which  resulted  from  an  increase  of  the  feed  protein 
has  been  computed  for  each  group. 

TABLE   140.  —  INFLUENCE  OF  PROTEIN   SUPPLY  ON  MILK  PRODUCTION 


SURPLUS  l  PROTEIN  AS  PER 
CENT  OF  MILK  PROTEIN 

PERCENTAGE  IN- 
CREASE or  YIELD 

NUM- 

BER OF 
EX- 

In Low  Protein 

RATIONS 

PERI- 

Rations 

In  High 

MENTS 

Protein 

Rations 

Milk 

Milk 

Range 

Average 

Solids 

Fat 

Less  than 

I 

150 

121 

231 

+  27.4 

+  23-5 

Protein      substituted 

5 

150-249 

194 

334 

+    7-2 

-     7-6 

for  fat 

Q 

2^0—  340 

200 

CAQ 

+     2.1 

—  IO.I 

y 

2 

^  o     o^y 
350-449 

411 

o^y 

525 

+     8.9 

2 

450-549 

450 

412 

-     9.6 

-  14.5 

19 

7 

150-249 

214 

348 

+  12.8 

+    6.6 

6 

250-349 

311 

437 

+  18.9 

+    7-1 

Protein      substituted 

8 

350-449 

374 

429 

+  7.1 

+    5-5 

for  carbohydrates  . 

4 

450-549 

492 

641 

+    8.8 

+    5-6 

i 

550-649 

637 

742 

+  25.6 

+  27.6 

2 

650-749 

669 

534 

+  69-5 

+  54-7 

3 

750- 

802 

897 

+  20.3 

+  18.4 

3i 

On  the  whole,  Morgen's  investigations  seem  to  furnish  con- 
clusive evidence  of  a  stimulating  effect  of  protein  on  milk  pro- 
duction. Even  when  the  protein  supply  already  largely  exceeded 
the  minimum  demand,  a  further  addition  was  in  most  instances 
followed  by  a  distinct  increase  in  the  yield  of  milk  solids  and 
usually  in  that  of  milk  fat.  It  should  be  said,  however,  that  a 
respectable  minority  of  the  individual  experiments  failed  to 
show  this  effect.  Of  the  nineteen  single  trials  in  which  protein 
was  substituted  for  fat,  eleven  showed  an  increased  yield  of 
milk  solids  and  six  an  increased  yield  of  milk  fat.  Out  of  the 

1  Digestible  protein  minus  requirements  for  maintenance  and  for  growth  of  wool. 


506  NUTRITION  OF  FARM  ANIMALS 

thirty-one  trials  in  which  protein  was  substituted  for  carbo- 
hydrates, twenty-six  showed  an  increased  yield  of  milk  solids 
and  twenty-one  an  increased  yield  of  milk  fat.  In  thirteen  out 
of  the  entire  fifty  experiments,  therefore,  the  presence  of  ad- 
ditional protein  failed  to  cause  an  increase  in  the  milk  solids, 
while  in  twenty-three  trials  it  failed  to  produce  an  increase  of 
milk  fat. 

600.  Effect  of  protein-rich  feeds.  —  In  addition  to  investiga- 
tions like  those  noted  in  the  last  paragraph,  in  which  the  effect 
of  an  interchange  of  practically  pure  nutrients  was  studied,  a 
considerable  number  of  experiments  are  on  record  in  which  an 
enrichment  of  a  ration  in  digestible  protein  has  been  effected 
by  an  interchange  of  feeding  stuffs,  as  for  example,  by  the 
substitution  of  cottonseed  meal  for  maize  meal. 

In  all  these  experiments  the  low  protein  rations  contained, 
with  one  or  two  exceptions,  a  surplus  of  digestible  protein  above 
the  milk  protein  plus  the  estimated  maintenance,  yet  a  further 
increase  of  digestible  protein  was  followed  by  a  larger  yield 
of  milk  per  unit  of  organic  matter  digested,  the  increase  rang- 
ing from  i  per  cent  to  39  per  cent.  As  in  the  experiments 
described  in  the  previous  paragraph,  the  results  appear  some- 
what capricious,  showing  no  consistent  relation  between  the 
excess  of  protein  supplied  and  the  relative  increase  of  milk  pro- 
duction secured. 

It  should  be  added  that  in  many  of  these  experiments  the 
proteins  of  the  low-protein  rations  consisted  to  a  considerable 
extent  of  maize  protein,  which  has  since  been  shown  to  be  of 
inferior  nutritive  value  (783) . 

601.  Protein  fed  in  American  practice.  —  On  the  basis  of 
experiments  and  observations,  Wolff  l  recommended  a  standard 
for  dairy  feeding  calling  for  2.5  pounds  of  digestible  protein 
daily  per  1000  pounds  of  live  weight.     Although  later  modified 
by  Lehmann,  this  standard  was  for  many  years  almost  uni- 
versally accepted  on  Wolff's  authority,  supported  by  the  un- 
doubted fact  that  in  many  instances  the  addition  of  protein-rich 
feeding  stuffs  to  ordinary  farm  rations  materially  increased  the 
milk  yield.     Later   observations,   however,   seem   to   indicate 
that  while  protein  is  important  the  amount  necessary  in  practice 
has  been  somewhat  overestimated. 

1  Die  Ernahrung  der  landw.  Nutzticre,  1876,  p.  548. 


MILK  PRODUCTION 


5°7 


Woll l  was  the  first  to  make  an  extensive  study  of  dairy 
practice  in  the  United  States  as  regards  the  protein  supply, 
finding  that  very  many  successful  dairymen  were  using  rations 
supplying  materially  less  protein  than  was  called  for  by  Wolff's 
standard.  The  average  of  all  the  rations  reported  as  compared 
with  Wolff's  standard  was  as  follows :  — 

TABLE  141.  —  DIGESTIBLE  MATTER  IN  DAIRY  RATIONS 


WOLFF'S  STAND- 
ARD 

WOLL'S  AVER- 
AGE 

Dry  matter  •  

24.0  Lb. 

2AXI  Lb. 

Digestible  matter 
Protein 

2X  Lb. 

2.15  Lb. 

Carbohydrates    
Fat 

12.5  Lb. 
o  4.  Lb. 

13.27  Lb. 
0.74  Lb. 

Nutritive  ratio  ...          .          .... 

i  :  ^.4 

i  :  S.Q 

Woll  points  out  that  this  average,  while  it  does  not  represent 
any  scientific  investigation  of  milk  production,  expresses  the 
results  of  American  feeding  experience,  and  although  it  does  not 
demonstrate  either  that  less  protein  would  not  be  sufficient  or 
that  more  would  not  be  advantageous,  it  does  afford  a  safe 
guide  for  practice,  and  indicates  that  rations  containing  less 
protein  than  the  Wolff  standard  calls  for  are  probably  more 
profitable. 

Somewhat  similar  observations  were  reported  by  Phelps 2 
in  1892-1893  with  the  additional  feature  that  in  several  in- 
stances the  rations  fed  were  subsequently  modified  at  the  sug- 
gestion of  the  experimenter  and  the  yield  on  the  new  ration 
determined.  Phelps  recommends  a  supply  of  1.9  to  2.5  pounds 
digestible  protein  per  head  according  to  the  productiveness  of 
the  cow,  the  amount  to  be  based  on  the  yield  of  milk  rather  than 
on  the  live  weight,  and  believes  such  rations  will  give  more 
economical  production  than  those  containing  less  protein. 

602.  Experiments  on  herds.  —  Haecker 3  has  reported  ex- 
tensive observations  and  experiments  on  the  protein  supply 

1  Wis.  Expt.  Sta.,  Buls.  33  (1892)  and  38  (1894). 

2  Conn.  (Storrs)  Expt.  Sta.,  Rpt.  1897,  pp.  17-66. 

3  Minn.  Expt.  Sta.,  Buls.  71,  79,  and  140. 


508 


NUTRITION  OF  FARM   ANIMALS 


of  the  dairy  herd  of  the  Minnesota  Station,  leading  to  the  con- 
clusion that  the  Wolff-Lehmann  standard  calls  for  unnecessarily 
large  amou'nts  of  protein. 

During  nine  years,  yields  which  were  regarded  as  normal  and 
satisfactory,  either  on  the  basis  of  total  amounts  produced  or 
of  feed  consumed  per  unit  of  milk,  were  secured  on  rations  con- 
taining, with  the  exception  of  the  year  1895-1896,  about  2 
pounds  of  digestible  protein  per  1000  pounds  live  weight.1 

During  three  of  these  years,  comparisons  were  also  made 
between  a  group  of  cows  receiving  about  2  pounds  of  digestible 
protein  per  day  and  1000  pounds  live  weight  and  one  receiving 
about  1.5  pounds.  In  the  earlier  years  the  low  protein  rations 
appeared  as  efficient  as  the  higher  ones,  but  toward  the  end  of 
the  three  years  the  low  protein  group  showed  deficient  vitality, 
apparently  indicating  a  lack  of  protein. 

In  all  nine  years,  the  (estimated)  digestible  protein  in  the 
high  protein  rations  supplied  a  considerable  surplus  over  the 
protein  of  milk  plus  maintenance.  Estimating  the  mainte- 
nance requirement  of  protein  at  0.7  per  1000,  Haecker  makes 
the  following  comparisons : 2 

TABLE  142.  —  PROTEIN  SUPPLY  OF  DAIRY  HERD 


DIGESTIBLE  PROTEIN 

AVAILABLE 

YEAR 

PROTEIN 
IN  MILK 

PROTEIN 
TO  i  POUND 
PROTEIN 
IN  MILK 

In  Feed 

For  Main- 
tenance 

Available 
for  Milk 

Lb. 

Lb. 

Lb. 

Lb. 

Lb. 

1894-1895  .... 

2.00 

0.67 

1-33 

0.814 

•63 

1902-1903  .... 

.92 

.62 

1.30 

•793 

.64 

1903-1904  .... 

•97 

.64 

i-33 

•747 

.78 

1904-1905  .... 

^21 

_^ 

liH2 

^769 

.68 

Average  .... 

•95 

•64 

1-31 

.781 

.68 

1905-1906  .... 

•63 

.60 

1.03 

.772 

•33 

1906-1907  .     .     .     . 

•74 

.64 

I.IO 

•803 

•37 

1907-1908  .... 

•75 

.61 

1.14 

•823 

•38 

1908-1909  .... 

.86 

.66 

i.  20 

.828 

1-45 

Average  .... 

1.74 

•63 

i.  ii 

.806 

1.38 

1  Bui.  140,  p.  43. 


2  Ibid.,  p.  54. 


MILK  PRODUCTION 


5°9 


The  protein  content  of  the  milk  from  the  low  protein  groups 
is  not  reported,  but  an  approximate  estimate  indicates  that  it 
could  not  have  been  much  less  than  the  surplus  of  feed  protein 
over  maintenance,  thus  furnishing  further  instances  of  an  ap- 
parently high  percentage  utilization  of  feed  protein  (586). 
While  the  indications  are  that  such  very  low  protein  rations 
were  inadequate,  it  seems  clear  that  a  surplus  of  40  or  50  per 
cent  of  available  protein  over  that  contained  in  the  milk  was 
ample  to  support  normal  production. 

Woll 1  has  reported  a  nine-year  series  of  observations  on  the 
dairy  herd  of  the  Wisconsin  Station,  the  time  being  divided  into 
three  periods  of  three  years  each,  during  the  first  and  third  of 
which  the  rations  had  a  nutritive  ratio  of  1:7,  while  during  the 
second  three  years  it  was  i :  6.  The  estimated  digestible  pro- 
tein consumed  per  day  by  cows  weighing  slightly  over  1000 
pounds  was 

Average  of  periods  A  and  C  1.76  pounds. 
Average  of  period  B  1.97  pounds. 


TABLE  143.  —  SURPLUS  or  AVAILABLE  PROTEIN  IN  HERD  RATIONS 


AVAILABLE 
PROTEIN 

MILK 
PROTEIN 

SURPLUS  OF 
AVAILABLE 
PROTEIN 

Lb. 

Lb. 

Per  Cent 

Period  A,  Low  protein  .  .  .  .  < 
Average  .  .  .  . 

1.03 
1.41 
1.18 

1.  21 

0.72 
0.80 
0.69 
0.74 

43 
76 

71 
63 

Period  C,  Low  protein  .  .  .  .  < 
Average 

0.82 
I.  II 
1.07 
I.OO 

0.58 

0-73 

0.76 

O.6o 

4i 
52 
4i 
4? 

Period  B,  High  protein  .  .  .  .  < 
Average  

1-54 
1.18 

1.22 

i«3i 

0.70 

o-59 

0.63 

0.64 

1  2O 
100 

94 
105 

VVis.  Expt.  Sta.,  Research  Bui.  13. 


510  NUTRITION  OF  FARM  ANIMALS 

The  results  for  the  entire  year  and  likewise  for  the  winter  rations 
showed  on  the  whole  a  somewhat  greater  and  a  decidedly  more 
economical  average  production  on  the  smaller  supply  of  pro- 
tein. The  protein  content  of  the  milk  is  not  stated,  but  esti- 
mating it  at  3.38  per  cent  and  allowing  0.6  pound  per  1000  for 
protein  maintenance,  the  approximate  surplus  of  thfe  available 
protein  (digestible  protein  minus  maintenance  requirement) 
over  the  milk  production  in  the  winter  rations  was  as  shown 
in  Table  143  in  each  of  the  nine  years. 

603.  Summary.  —  In  view  of  the  great  differences  between 
individual  cows  both  as  to  yield  and  composition  of  milk,  it  is 
clear  that  no  one  figure  can  express  the  protein  requirement  for 
milk  production  per  day  and  head,  but  that  it  must  vary  with 
the  amount  and  character  of  the  milk  produced. 

It  appears  to  be  fairly  well  established  (586)  that  the  digesti- 
ble feed  protein  of  ordinary  mixed  rations  may  be  converted 
into  milk  protein  without  any  very  great  loss  and  that  conse- 
quently a  moderate  rate  of  milk  production  may  be  maintained, 
at  least  for  a  time,  on  rations  furnishing  a  comparatively  small 
surplus  of  digestible  protein  over  the  milk  protein  plus  the 
requirement  for  maintenance. 

On  the  other  hand,  however  (599,  600),  both  experiments  with 
pure  proteins  and  those  in  which  an  increase  in  the  protein  con- 
tent of  rations  has  been  secured  by  the  use  of  protein-rich  feeds 
seem  to  indicate  clearly  a  stimulating  influence  of  excess  protein 
on  milk  production,  although  in  the  majority  of  cases  the  effect 
was  not  very  large.  Contrary  to  what  might  have  been  antici- 
pated, however,  an  increase  in  the  digestible  protein  of  the  ration 
appears  to  have  been  on  the  whole  quite  as  effective  with  ani- 
mals already  on  a  high  plane  of  protein  nutrition,  i.e.,  receiving 
a  large  surplus  over  the  minimum  requirement  as  with  those 
on  a  much  lower  level  of  protein  supply.  This  appears 
with  especial  clearness  in  Morgen's  experiments  on  sheep. 
The  results  therefore  fail  to  indicate  the  limits  within  which 
this  stimulating  effect  is  manifest  or  to  establish  any  quantitative 
relation  between  the  surplus  protein  supplied  and  the  additional 
milk  yielded.  They  afford  no  basis,  therefore,  for  any  estimate 
of  the  extent  to  which  a  stimulation  of  milk  production  by  means 
of  excess  protein  will  be  economically  profitable  under  any  given 
conditions. 


MILK  PRODUCTION 


The  experiments  by  Haecker  and  by  Woll  on  herds  (602) 
seem  to  justify  the  conclusion  that  in  commercial  milk  produc- 
tion in  the  United  States  a  ration  supplying,  in  addition  to  the 
maintenance  requirement,  digestible  protein  equal  to  150  to 
1 60  per  cent  of  the  milk  protein  yielded  is  ample  in  this  respect 
to  sustain  a  normal  rate  of  milk  production  and  may  be  dis- 
tinctly more  profitable  than  a  ration  richer  in  protein.  It  is 
not  impossible,  however,  that  when  circumstances  warrant 
the  effort  to  secure  the  maximum  production  possible  to  the 
animal  a  more  liberal  supply  of  protein  would  be  advantageous. 

Energy  requirements  for  milk  production 

604.  Energy  content  of  milk.  —  As  in  other  forms  of  stock 
feeding,  the  principal  factor  in  determining  the  energy  required 
in  the  feed  is  the  amount  of  chemical  energy  contained  in  a 
unit  of  product.  In  the  case  of  milk  production  this  factor 
varies  through  a  wide  range  on  account  of  the  large  differences 
in  composition  of  milk  due  to  individual  and  breed  differences, 
stage  of  lactation,  etc. 

Haecker  1  has  arranged  the  results  of  analyses  of  543  samples 
of  milk  in  ten  groups  according  to  the  fat  content.  His  averages, 
together  with  the  energy  content  per  pound  of  milk  as  computed 
by  the  writer,  are  as  shown  in  the  following  table :  — 

TABLE  144.  —  COMPOSITION  AND  ENERGY  VALUE  OF  MILK 


NUMBER  OF 

COMPOSITION 

TOTAL 
ENERGY  PER 
POUND 

Samples 

Milkings 

Fat 

Protein 

Carbohy- 
drates 

% 

% 

% 

Cals. 

— 

— 

2-5 

2-55 

4-45 

253 

47 

658 

3-o 

2.68 

4.60 

278 

55 

770 

3-5 

2.81 

4-75 

3°6 

57 

798 

4.0 

3.08 

4.85 

336 

116 

1624 

4-5 

3-27 

4-97 

365 

103 

1442 

5-0 

3-45 

4-99 

390 

89 

1246 

5-5 

3.65 

4.92 

415 

39 

546 

6.0 

3-82 

4.91 

440 

24 

336 

6-5 

4.02 

4.90 

467 

13 

182 

7.0 

4.22 

4.84 

492 

Minn.  Expt.  Sta.,  Bui.  140,  p.  51. 


512  NUTRITION  OF  FARM  ANIMALS 

If  there  were  available  definite  knowledge  regarding  the  net 
energy  values  of  feeding  stuffs  for  milk  production,  the  fore- 
going figures  for  the  total  energy  of  the  milk  would  serve 
as  a  basis  for  estimating  the  net  energy  supply  required  for 
the  production  of  a  given  yield  of  milk  for  any  one  of  the 
ten  grades,  25  pounds  of  4  per  cent  milk,  for  example,  requiring 
336  X  25  =  8400  Cals.  of  net  energy  in  the  feed. 

605.  Equivalent  energy  values  for  fattening.  —  In  the  ab- 
sence of  determinations  of  the  net  energy  values  of  feeding  stuffs 
for  milk  production  (588)  it  is  impossible  to  make  direct  use,  in 
the  manner  just  indicated,  of  the  foregoing  data  regarding  the 
energy  content  of  milk.  Pending  such  determinations,  however, 
it  appears  possible  to  estimate  the  net  energy  requirements  in 
the  feed  of  dairy  cows  in  another  way,  viz.,  by  computing  from 
the  composition  of  the  milk,  in  the  manner  already  described 
(593),  the  amount  of  fattening  which  is  equivalent  in  energy 
requirement  to  a  unit  of  milk  yield.  Thus  it  was  estimated, 
on  certain  assumptions,  that  the  amount  of  feed  energy  required 
for  the  production  of  one  pound  of  average  4  per  cent  milk  would, 
if  applied  to  fattening,  have  produced  a  gain  of  only  252  Cals. 
in  place  of  the  336  Cals.  actually  present  in  the  milk.  Accord- 
ingly, a  ration  containing,  in  excess  of  maintenance,  252  Cals. 
of  net  energy  for  fattening  would  have  been  adequate  to  pro- 
duce a  pound  of  milk  containing  336  Cals.  of  energy.  In 
this  way  the  amount  of  net  energy  required  for  the  production 
of  one  pound  of  milk  of  each  of  the  grades  included  in  the 
previous  table  may  be  computed. 

By  this  device  of  reducing  the  total  energy  content  of  the  milk 
to  the  equivalent  amount  of  net  energy  for  fattening,  it  appears 
possible  to  utilize  the  net  energy  values  of  feeds  obtained  by 
Kellner  and  others  in  maintenance  or  fattening  experiments 
as  a  basis  for  computing  rations  for  milk.  Such  a  method  is,  of 
course,  provisional,  and  the  basis  for  it  at  present  is  somewhat 
slender,  but  it  seems  the  best  one  now  available.  In  its  actual 
use  for  computing  rations,  however,  it  appears  necessary  also 
to  take  into  account  the  fact  shown  by  Eckles  (722)  that  with 
well-fed  cows  the  digestibility  of  the  rations  is  on  the  average 
some  5  per  cent  lower  than  the  average  digestion  coefficients 
which  are  used  in  computing  net  energy  values.  Accordingly, 
the  figures  for  the  equivalent  energy  for  fattening  as  computed 


MILK  PRODUCTION 


513 


for  the  several  grades  of  milk  have  been  increased  by  5  per  cent, 
giving  the  following  results,  which  may  be  used  provisionally 
to  compute  from  the  figures  of  Table  VII  of  the  Appendix 
the  rations  required  for  the  production  of  milk  of  different 
grades. 

TABLE  145.  —  EQUIVALENT  ENERGY  VALUES  FOR  FATTENING 


PER  CENT  FAT  IN  MILK 

EQUIVALENT  ENERGY  VALUES  PER  LB. 

i                OF  MlLK1 

Cals. 

2-5 

190 

3.0 

214 

3-5 

238    , 

4.0 

265^*"* 

4-5 

291 

5.0 

315 

5-5 

338 

6.0 

361 

6-5 

385 

7.0 

408 

606.  Concurrent  fattening.  —  Were  all  the  surplus  feed  above 
the  maintenance  requirement  applied  to  milk  production,  it 
would  be  a  comparatively  simple  matter  to  compute  the  amount 
of  feed  energy  required  in  a  daily  ration.  Thus,  if  a  cow  weigh- 
ing 1000  pounds  were  capable  of  producing  25  pounds  of  4.5 
per  cent  milk  daily,  the  net  energy  required  in  her  ration  would 
be  computed  as  follows :  - 


For  milk  production  25  Ib.  of  milk  ©291  Cals. 
For  maintenance 


7.275  Therms 

6.000  Therms 

13.275  Therms 


Attention  has  been  called  several  times,  however,  to  the 
fact  that  in  the  milking  animal  at  least  two  forms  of  production 
are  possible,  viz.,  milk  and  increase  of  body  tissue  (fattening), 
only  the  former  of  which  is  usually  desired.  To  these  may 
perhaps  be  added,  as  a  third  form  of  production,  a  possible 
stimulation  of  the  incidental  muscular  activity  of  the  animal 
by  heavy  feeding  (609).  Evidently  if  conditions  are  such  that 

1  Including  5  per  cent  allowance  for  difference  in  digestibility. 
2  L 


514  NUTRITION  OF  FARM  ANIMALS 

part  of  the  feed  energy  is  diverted  to  these  other  purposes,  the 
ration  must  supply  more  net  energy  per  pound  of  milk  than 
would  be  necessary  if  all  the  latter  were  utilized  for  milk  pro- 
duction. 

607.  Influence  of  plane  of  nutrition.  —  It  appears  to  be  well 
established  both  by  common  experience  and  by  direct  experi- 
ment that  such  a  diversion  of  energy  from  milk  production  to 
other  forms  may  in  fact  take  place  before  the  maximum  capacity 
of  the  milk  glands  is  reached.     On  moderate  rations,  the  net 
energy,   after   satisfying   the   maintenance   requirement,   may 
apparently  be  utilized  entirely  for  milk  production.     As  the 
feed  is  increased,  however,  the  animal  does  not  continue  to 
utilize  all  the  available  net  energy  for  milk  production  up  to 
the  limit  of  its  capacity  and  then  suddenly  begin  to  utilize  any 
surplus  for  fattening.     On  the  heavier  rations  the  concentration 
of  the  digested  nutrients  in  the  body  fluids  increases,  the  organ- 
ism reaches  a  higher  plane  of  nutrition,  and  at  a  point  varying 
with  different  individuals  this  greater  concentration  of  available 
material  causes  fattening  to  begin,  which,  so  to  speak,  robs  the 
milk  glands  of  feed  intended  for  milk  production. 

608.  Influence  of  individuality.  —  The  individuality  of  the 
animal  is  a  most  important  factor  in  this  connection.     With 
cows  having  an  inherited  tendency  toward  fattening,  as  in  the 
so-called  beef  breeds,  this  point  at  which  energy  begins  to  be 
divided  between  milk  production  and  fattening  may  be  reached 
on  comparatively  light  rations.     Such  animals  can  be  brought 
up  to  their  maximum  milk-producing  capacity    only  at  the 
expense  of  a  considerable  expenditure  of  feed  for  concurrent 
fattening  and  are  likely  to  be  unprofitable  for  dairy  purposes. 
On  light  rations,  giving  a  moderate  yield  of  milk,  the  mainte- 
nance requirement  constitutes  too  large  a  proportion  of  the  feed 
cost,  while  with  heavier  feeding  production  is  directed  too 
largely  to  fattening. 

With  the  typical  dairy  animal,  on  the  other  hand,  having 
but  a  slight  tendency  to  fatten,  the  feed  may  be  increased  well 
towards  the  amount  required  to  support  the  maximum  capacity 
of  the  milk  glands,  or  in  exceptional  cases  even  up  to  that  point, 
without  causing  any  material  diversion  to  fattening.  Such 
animals,  especially  if  of  large  milk-producing  capacity,  are  the 
profitable  dairy  animals  so  far  as  the  cost  of  feed  is  concerned. 


MILK  PRODUCTION  515 

The  relations  between  feed  supply,  milk  production  and  fatten- 
ing outlined  in  the  foregoing  paragraphs  have  been  clearly 
demonstrated  in  a  number  of  investigations  on  dairy  feeding, 
such  as  those  of  Waters,  Caldwell  and  Weld  l  and  of  Waters 
and  Hess  2  at  the  Pennsylvania  station,  those  by  Woll  and 
Carlyle3  at  the  Wisconsin  station,  and  especially  those  by 
Haecker  4  at  the  Minnesota  station. 

609.  Stimulation  of  katabolism.  —  But  while  the  diminish- 
ing returns  obtained  from  the  feed  of  the  dairy  cow  as  its  amount 
is  increased  beyond  a  certain  maximum  may  be  explained  in 
part  by  a  diversion  of  net  energy  from  milk  production  to  fat- 
tening, it  seems  to  be  true  also  that  heavier  feeding  may  cause 
a  larger  proportion  of  the  digested  organic  matter  to  be  oxidized, 
either  as  the  result  of  greater  muscular  activity  or  by  a  direct 
stimulation  of  the  katabolic  processes.     This  is  especially  evident 
in  breed  tests  in  which  heavy  rations  have  been  consumed. 
Striking  illustrations  of  it  are  afforded  by  the  results  of  the 
tests  of  dairy  breeds  at  the  Louisiana  Purchase  Exposition  in 
1904  as  computed  by  Haecker 5  and  by  the  extensive  comparisons 
of  German  breeds  reported  by  Hansen.6 

610.  Diminishing  returns  from  feed.  —  It  is  evident  from 
the  foregoing  that,  with  the  possible  exception  of  cows  of  a  very 
pronounced  dairy  type,  the  maximum    yield  of  milk  can  be 
secured  only  at  the  expense  of  a  simultaneous  production  of 
more  or  less  body  fat  and  perhaps  also  of  a  stimulation  of  the 
katabolic  processes  of  the  body.     Consequently,  beyond  the 
point  at  which  this  fattening  or  stimulation  begins,  the  milk 
production  per  unit  of  net  energy  in  the  feed  must  necessarily 
be  a  diminishing  one,  and  it  is  clear  that  the  determination  of 
the  net  energy  requirements  for  milk  production  is  to  a  consider- 
able extent  an  economic  problem. 

Milk  will  be  produced  at  the  least  feed  (energy)  cost  per 
pound  when  the  ration  is  so  adjusted  as  to  produce  as  great  a 
yield  of  milk  as  is  possible  without  causing  fattening.7  If  the 

1  Penna.  Expt.  Sta.,  Rpt.  1893,  p.  24-36.        2  Ibid.,  Rpt.  1895,  p.  24-55. 

3  Wis,  Expt.  Sta.,  iyth  Rpt.  (1900),  p.  37-61. 

4  Minn.  Expt.  Sta.,  Buls.  79  and  140.  5  Minn.  Expt.  Sta.,  Bui.  106,  p.  158. 
8Landw.  Jahrb.,  35  (1906),  Ergzbd.  IV,  147-236;   37  (1908),  Ergzbd.  Ill,  236- 

410;    2er  Ber.  vom  Dikopshof  (1911),  210,  430. 

7  It  may  be  presumed  that  the  stimulating  effect  upon  the  katabolism  occurs 
chiefly  in  heavy  feeding  which  causes  fattening  also. 


51 6  NUTRITION  OF  FARM  ANIMALS 

energy  supply  is  decreased  below  this  point  the  milk  yield  will 
tend  to  fall  off  while  the  maintenance  requirement  remains 
practically  constant.  The  maintenance,  therefore,  will  consume 
a  larger  percentage  of  the  total  feed  energy  so  that,  exactly  as 
in  growth  or  in  fattening,  while  the  net  energy  requirement 
for  the  formation  of  a  unit  of  milk  remains  approximately  con- 
stant, the  total  net  energy  necessary  to  support  both  main- 
tenance and  milk  production  increases  relatively  per  unit  of 
product. 

On  the  other  hand,  if  the  feed  is  increased  so  as  to  cause  fat- 
tening or  to  stimulate  katabolism,  it  is  clear  that  the  energy 
requirements  per  unit  of  milk  produced  will  be  apparently  in- 
creased for  the  reasons  already  explained.  Such  an  increase  in 
the  feed  cost,  however,  may  be  economically  justifiable  for  the 
same  reasons  as  in  the  case  of  any  form  of  intensive  production. 
In  average  commercial  milk  production,  it  may  be  doubted 
whether  the  rations  should  be  made  heavy  enough  to  cause  any 
considerable  fattening,  and  so  far  as  this  is  the  case,  the  esti- 
mated net  energy  values  per  unit  of  milk  in  Table  145  may 
serve  as  the  basis  for  computing  rations.  If,  however,  feed  is 
relatively  cheap  and  dairy  products  high  in  price,  the  diminish- 
ing returns  due  to  heavier  feeding  may  still  be  profitable  up 
to  a  certain  point  even  though  more  energy  per  unit  of  milk 
must  be  supplied  in  order  to  support  concurrent  fattening, 
while  the  fact  that  more  or  less  of  the  fat  stored  in  the  body 
may  be  utilized  for  the  support  of  milk  production  in  the  early 
stages  of  the  next  lactation  is  also  to  be  considered. 

Fat  requirement  for  milk  production 

611.  Is  fat  essential?  —  It  was  noted  in  discussing  the  func- 
tions of  the  nutrients  (265)  and  also  in  connection  with  the  re- 
quirements for  growth  (498,  499)  that  the  presence  in  the  feed 
of  certain  fats  or  of  substances  associated  with  them  appears  to 
be  essential  to  growth.  Since  milk  production  is  in  many  re- 
spects analogous  to  growth  it  is  of  interest  to  inquire  whether 
the  fats  of  the  feed  exert  any  such  specific  effect,  either  on  milk 
production  as  a  whole  or  on  the  production  of  milk  fat. 

That  milk  fat  as  well  as  body  fat  may  be  manufactured  in 
the  body  in  large  amounts  from  other  nutrients  has  been  shown 


MILK  PRODUCTION  517 

beyond  question  by  the  experiments  of  Voit,  Ktihn  and  Fleischer, 
M.  Fleisher,  Wolff  and  especially  by  those  of  Jordan,1  while 
the  latter  investigator  demonstrated  that  milk  fat  can  be 
formed  from  carbohydrates  (553).  Jordan's  experiments  on 
cows,  as  well  as  the  later  ones  of  Morgen 2  on  sheep  and  goats, 
likewise  show  that  relatively  large  amounts  of  milk  may  be 
produced  on  rations  made  up  of  feeding  stuffs  very  poor  in  fat 
or  from  which  the  larger  part  of  the  fat  has  been  extracted. 
It  is  scarcely  feasible  to  prepare  absolutely  fat-free  rations  for 
such  animals  and  the  writer  is  not  aware  of  any  experiments  on 
milk  production  with  such  rations,  but  it  is  clear  that  at  most 
but  very  small  amounts  of  fat  can  be  regarded  as  indispensable. 
612.  Addition  of  fat  to  rations.  —  Experiments  in  which  the 
fat  content  of  ordinary  rations  has  been  increased,  either  by 
the  direct  addition  of  fat  in  one  form  or  another  or  by  the  sub- 
stitution of  fat  for  carbohydrates,  have  given  very  contradic- 
tory results.  An  increased  percentage  of  fat  in  the  milk  has 
been  very  frequently  observed,  sometimes  accompanied  by  an 
increase  in  the  actual  yield  of  fat  and  sometimes  not,  while  in 
other  cases  the  results  have  been  entirely  negative.  In  many 
instances  the  experiments  are  complicated  by  the  fact  that  the 
fat  was  simply  added  to  a  basal  ration,  thus  increasing  the 
total  amount  of  feed.3  The  most  recent  investigations  are 
those  undertaken  upon  a  common  plan  under  the  auspices  of 
the  German  Agricultural  Council  at  ten  German  experiment 
stations  with,  in  all,  196  cows,  the  results  of  which  have  been 
reported  by  Kellner.4 

The  increase  in  the  fat  of  the  rations  was  effected  by  the  substitu- 
tion of  rice  feed  5  for  rye  meal  and  starch,  so  that  fat  replaced  an 
equivalent  amount  of  carbohydrates.  The  results,  therefore,  in- 
cluded any  "specific"  effects  of  these  two  feeding  stuffs,  if  such  there 
were  (618).  Per  1000  pounds  live  weight,  the  fat-poor  rations  con- 
tained 0.25  to  0.50  pound  digestible  fat  and  the  fat-rich  0.47  to  i.io 
pounds. 

1  N.  Y.  (Geneva)  Expt.  Sta.,  Buls.  132  (1897)  and  197  (1901). 

2  Landw.  Vers.  Stat.,  61  (1904),  i ;   62  (1905),  251 ;  64  (1906),  93. 

3  Compare  Kellner,  Die  Ernahrung  der  landw.  Nutztiere,  6th  Edition,  pp.  564-566. 

4  Reichsamt  des  Innern;   fieri chte  iiber  Landwirtschaft,  Heft  i  and  2. 

5  According  to  Hansen  rice  feed  has  the  specific  effect  of  depressing  the  fat  pro- 
duction, although  this  effect  did  not  appear  manifest  in  most  of  these  experiments 
nor  in  those  of  Fingerling  (613). 


NUTRITION  OF  FARM  ANIMALS 


Grouping  the  results  regarding  the  fat  content  of  the  milk 
according  to  the  total  amount  of  milk  yielded,  it  appears  that 
an  increase  in  the  percentage  of  fat  in  the  milk  was  in  general 
associated  with  a  decrease  in  the  total  yield  and  vice  versa. 

TABLE  146.  —  EFFECT  OF  INCREASING  FAT  OF  RATIONS 


EXPERIMENTS  AT 

PERCENTAGE  IN- 
CREASE  (+)  OR 
DECREASE  (—  )  or 
MILK  YIELD 

PERCENTAGE  IN- 
CREASE  (+)  OR 
DECREASE  (—  ) 
IN  FAT  CONTENT 
OF  MILK 

Danzig     
Bonn 

-  0.5  % 

—  2  S  % 

-    9-8% 
—    66% 

Pommritz                         .          .... 

-  7Q% 

+    1  1% 

Kiel     
Breslau 

+  0.2% 
—  3  I  % 

-    5-0% 
—    o  •*  % 

Triesdorf      
\Veihenstephan 

-2.3% 

—  7  I  % 

-    2.6% 
-1-    o  6  % 

Lauchstadt 

+  21% 

—    A  8% 

Darmstadt    
Jena 

-6.7% 

+  0   S  °7n 

-    1.0% 

—  10  8% 

Average    

-2.7% 

-    3-7% 

Striking  individual  differences  in  cows,  however,  were  ob- 
served. For  example,  in  two  of  the  experiments  the  range  of 
increase  or  decrease  for  the  individual  animals  consequent  on 
the  substitution  of  fat  for  carbohydrates  was  as  follows :  — 

TABLE  147.  —  INFLUENCE  OF  INDIVIDUALITY  ON  EFFECTS  OF  FAT  INCREASE 


EXPERIMENTS  AT 

INCREASE  (+)  OR 
DECREASE  (—  )  OF 
MILK  YIELD 

INCREASE  (+)  OR 

DECREASE  (—)  IN 
FAT  YIELD 

Lauchstadt  
Weihenstephan      

Kgs. 
+  1.85  to  —  2.24 

+  0.22  tO    —    2.0Q 

Grams 
+  53  to   -  92 
+  32  to   -  42 

It  seems  clear  from  the  foregoing  results  that  under  the 
average  conditions  of  practice  no  material  advantage  can  be 
expected  from  increasing  the  digestible  fat  of  dairy  rations 


MILK  PRODUCTION  519 

above  0.4  to  0.5  pound  per  1000  pounds  live  weight,  although  a 
gain  may  result  with  individual  cows. 

613.  The  minimum  of  feed  fat.  —  On  the  other  hand,  the 
extensive  investigations  by  Morgen  and  his  associates  on  sheep 
and  goats,  already  referred  to  (599) ,  have  shown  that  with  these 
animals  an  increase  of  the  fat  content  of  rations  exceptionally 
deficient  in  this  ingredient  results  in  most  cases  in  an  increased 
yield  of  milk  solids  and  especially  in  a  specific  increase  of  the 
fat  content  of  the  milk. 

The  rations  consisted  of  a  basis  of  roughage  poor  in  fat J  to  which 
various  commercially  pure  nutrients  were  added.  Fat  in  various 
forms  was  added  to  scant  basal  rations  and  likewise  substituted  for 
carbohydrates  or  protein  in  heavier  rations.  Experiments  of  the  latter 
sort,  in  which  the  energy  content  of  the  rations  was  kept  substantially 
unchanged,  are  especially  convincing.  An  increase  of  the  fat  content 
of  the  fat-poor  rations,  either  by  direct  addition  or  by  substitution, 
up  to  0.5  to  i.o  Ib.  per  1000  Ib.  live  weight  not  only  resulted  in  a 
distinct  increase  in  the  yield  of  milk  and  of  milk  solids  but  likewise 
in  an  increased  percentage  of  fat  in  the  fresh  milk  and  in  the  milk 
solids.  This  specific  influence  of  fat  as  compared  with  protein  is 
illustrated  in  Table  140,  which  shows  that  while  a  substitution  of 
protein  for  fat  or  for  carbohydrates  increased  the  yield  of  solids, 
-the  yield  of  fat  was  decreased  in  the  former  case.  Fingerling  2  has 
likewise  shown  that  increasing  the  fat  content  of  a  ration  by  substi- 
tuting a  feed  rich  in  fat  for  one  rich  in  carbohydrates  (rice  meal  in 
place  of  barley  meal)  likewise  increases  the  fat  yield. 

This  specific  effect  of  feed  fat  on  the  production  of  milk  fat 
appears  to  be  more  marked  in  the  case  of  sheep  and  goats  than 
in  the  case  of  cows.  It  was  observed  up  to  a  limit  of  approxi- 
mately i.o  pound  per  1000  pounds  live  weight,  but  above  that 
the  results  were  if  anything  negative,  while  with  cows,  as  al- 
ready shown,  an  increase  of  the  digestible  fat  above  0.4  pound 
per  1000  pounds  live  weight  generally  produces  little  or  no 
effect.  Morgen  ascribes  the  difference  to  the  greater  relative 
production  of  fat  per  unit  of  weight  by  the  smaller  animals. 

In  ordinary  dairy  rations  fat  will  not  often  fall  below  the 
apparent  limit  of  0.4  to  0.5  pound.  Only  when  feeds  unusually 
poor  in  fat  are  used,  such  as  straw  or  inferior  grades  of  hay  or 

1  In  part  artificially  extracted.  2  Landw.  Vers.  Stat.,  64  (1906),  299. 


520  NUTRITION  OF  FARM  ANIMALS 

by-products  containing  a  minimum  of  fat,  may  a  favorable 
effect  upon  the  yield  of  milk  and  its  percentage  of  fat  be  antici- 
pated from  an  increase  in  the  supply  of  digestible  fat. 

614.  Influence  on  utilization  of  energy.  —  None  of  the  ex- 
periments on  the  influence  of  the  fat  supply  upon  milk  production 
afford  any  exact  data  regarding  the  concurrent  gain  or  loss  of 
tissue,  since  no  determinations  of  the  gaseous  excreta  were  made. 
It  is  impossible,  therefore,  to  determine  whether  the  observed 
effect  of  the  feed  fat  was  brought  about  by  a  stimulation  of  milk 
production  at  the  expense  of  fattening,  i.e.,  by  modifying  the 
direction  in  which  the  energy  of  the  feed  was  utilized,  or  whether, 
under  its  influence,  the  metabolism  in  the  milk  gland  was  actu- 
ally effected  more  economically. 

Ash  requirements  for  milk  production 

Practically  no  data  are  on  record  upon  which  a  trustworthy 
estimate  of  the  ash  requirements  of  the  dairy  cow  can  be  based. 

615.  The  outgo  in  the  milk.  —  It  is  true  that  the  outgo  of 
mineral  elements  in  the  milk  may  be  determined  without  special 
difficulty  and  that  reasonably  accurate  figures  are  available 
from  which  it  may  be  estimated.     This,  however,  is  but  a  single 
element  in  the  problem.    It  became  evident  in  considering  the 
ash  requirements  for  maintenance   in   Chapter  IX  (421-436) 
and  those  for  growth  in  Chapter  XI  (492-497)  that  neither  the 
actual  availability  of  the  mineral  elements  of  feeding  stuffs 
nor  the  influence  of  the  amount  and  quality  of  the  ash  supply 
upon  the  losses  in  feces  and  urine  has  been  sufficiently  investi- 
gated to  permit  any  satisfactory  conclusions  as  to  the  influence 
of  these  factors. 

Kellner  1  has,  however,  computed  the  approximate  require- 
ments for  calcium  and  phosphorus  from  the  outgo  in  the  milk. 
Accepting  Henneberg's  estimate  of  71.4  grams  of  calcium  and 
21.8  grams  of  phosphorus  per  1000  kilograms  live  weight  for  the 
maintenance  requirements,  he  adds  to  these  three  times  the 
average  amounts  found  in  the  milk  upon  the  somewhat  ques- 
tionable assumption  that  only  one-third  to  one-half  the  feed 
ash  is  available.  Computed  for  a  yield  of  20  pounds  of  milk 
per  day  by  a  thousand  pound  cow,  his  results  are  as  follows :  — 

1  Ernahrung  landw.  Nutztiere,  6th  Ed.,  p.  595. 


MILK   PRODUCTION  521 

TABLE  148.  —  ESTIMATED  REQUIREMENTS  FOR  MILK  PRODUCTION 


CALCIUM 

PHOS- 
PHORUS 

Grams 

Grams 

For  maintenance  per  1000  Ib.      

32 

10 

For  production  of  20  Ib.  of  milk      ....... 

29 

15 

Total 

61 

2  ^ 

616.  The  supply  in  the  feed.  —  Kellner  states  that  ordinary 
dairy  rations  will  usually  meet  the  requirements  just  stated  and 
that  only  in  exceptional  cases  will  it  be  necessary  to  supplement 
the  calcium  supply. 

Forbes  1  has  shown,  however,  that  rations  fully  adequate,  so 
far  as  organic  nutrients  are  concerned,  to  support  a  considerably 
greater  milk  production  than  that  on  which  Kellner 's  require- 
ments are  based  may  nevertheless  permit  very  material  losses 
of  mineral  ingredients,  especially  of  calcium,  magnesium  and 
phosphorus.  Complete  ash  balances  are  reported  for  six 
animals  on  three  different  rations,  all  of  which  maintained  the 
live  weights  of  the  cows  and  resulted  in  gains  of  body  protein. 
With  an  average  live  weight  of  about  935  pounds  and  an  average 
daily  milk  yield  of  about  36  pounds  (16.38  Kgs.),  the  calcium 
and  phosphorus  requirements  as  computed  according  to  Kell- 
ner's  method  and  the  actual  amounts  supplied  in  the  rations 
were :  — 

TABLE  149.  —  CALCIUM  AND  PHOSPHORUS  FOR  MILK  PRODUCTION 


CALCIUM 

PHOS- 
PHORUS 

Estimated  according  to  Kellner 
For  maintenance  —  935  Ib 

Grams 

•2  I 

Grams 

For  production  of  36  Ib.  of  milk        

4.4. 

•27 

Total    

7e 

46 

Average  contained  in  ration 

A  -I 

28 

Average  daily  losses  from  the  body      

16 

I  7 

1  Ohio  Expt.  Sta.,  Bui.  275  (1916). 


522  NUTRITION  OF  FARM   ANIMALS 

Whether  such  relatively  large  losses  by  fresh  cows  usually 
accompany  copious  milk  production  and  are  made  up  again  in 
the  later  stages  of  lactation,  and  whether  this  depletion  of  the 
mineral  reserves  of  the  body  is  one  of  the  factors  in  the  natural 
shrinkage  of  milk  production,  as  suggested  by  Forbes,  are 
matters  for  future  investigation. 

It  is  evident,  however,  that  none  of  the  foregoing  data  afford 
much  information  regarding  the  real  ash  requirements  of  dairy 
cows. 

Feed  as  a  stimulus  to  milk  production 

617.  Flavoring  substances.  —  By  flavoring  substances  is 
meant  those  whose  presence  in  small  amounts  improves  the 
odor  or  taste  of  a  feeding  stuff  or  ration  while  not  adding  ma- 
terially to  its  content  of  protein  or  energy.  In  other  words,  they 
are  substances  which  do  not  yield  matter  or  energy  to  the  body 
in  the  ordinary  sense,  but  which  may  nevertheless  affect  the 
course  or  rapidity  of  metabolism. 

That  the  flavor  or  aroma  of  feeding  stuffs  is  not  an  insignif- 
icant element  in  determining  their  commercial  value,  not  only 
for  milk  production  but  for  other  purposes,  is  well  established 
by  practical  experience.  This  superiority  is  doubtless  due 
largely  to  the  fact  that  a  palatable  feed  is  consumed  more  freely 
than  one  lacking  in  flavor.  In  the  case  of  milk  production, 
however,  it  appears  that,  within  certain  rather  narrow  limits, 
various  flavoring  materials  may  act  as  a  direct  stimulus  to  the 
milk  gland,  causing  a  greater  yield  of  milk  and  especially  of  fat. 

In  Morgen's  experiments  on  milk  production  cited  on  previous 
pages  extensive  use  was  made  of  rations  consisting  largely  of 
almost  flavorless  materials.  With  such  rations  it  was  found 
to  be  impossible  to  secure  yields  equal  to  those  obtained  from 
rations  supplying  equal  amounts  of  protein  and  energy  but 
made  up  of  normal  feeds.  The  addition  to  these  flavorless 
rations,  however,  of  such  substances  as  fennel,  anise  or  hay 
distillate,  or  the  introduction  of  malt  sprouts,  caused  a  distinct 
increase  in  the  milk  yield,  so  that,  with  rations  containing  a 
sufficiency  of  fat,  almost  or  quite  normal  results  were  secured.1 
Moreover,  a  distinct  effect  was  observed  in  increasing  the  fat 
production  and  the  percentage  of  fat  in  the  milk. 

1  Landw.  Vers.  Stat.,  61  (1904),  i- 


MILK  PRODUCTION  523 

Subsequent  experiments  by  Fingerling  1  fully  confirmed  these 
results.  The  addition  to  the  flavorless  rations,  or  to  damaged 
hay,  of  salt,  hay  distillate,  fennel,  or  even  the  impregnation  of 
rations  with  the  odor  of  the  latter  substances,  caused  a  marked 
increase  in  the  yield  of  milk  and  in  its  content  of  fat  as  well  as 
in  the  percentage  of  fat  in  the  milk  solids,  while  similar  additions 
to  normal  rations  were  without  effect.  Fingerling's  experi- 
ments likewise  show  clearly,  however,  that  this  effect  of  flavor- 
ing materials,  while  of  much  physiological  interest,  can  rarely 
be  of  much  economic  importance  and  they  lend  no  support  to 
the  claims  of  the  numerous  condimental  feeds,  milk  powders, 
etc.,  so  largely  advertised.  It  was  also  shown  that  certain 
feeding  stuffs  (malt  sprouts,  palmnut  cake,  cocoa  cake  and 
beet  molasses)  when  added  to  a  ration  of  damaged  hay  and  pure 
nutrients  increased  the  milk  and  fat  yields  to  about  the  same 
extent  as  flavoring  with  fennel.  Whether  these  effects  are  due 
to  some  form  of  nerve  stimulus,  either  general  or  specific,  or  to 
an  increased  production  of  the  hormones  of  milk  production 
(549)  does  not  appear. 

618.  Specific  effects  of  feeds.  —  The  fact  just  noted  that 
certain  feeds  stimulate  the  production  of  milk  and  of  milk  fat, 
appparently  by  their  influence  on  the  flavor  of  rations,  leads 
naturally  to  a  consideration  of  the  so-called  "  specific  "  effects 
of  feeds  in  general.  The  belief  has  long  been  held  in  practice 
that  feeding  stuffs  may  promote  milk  production  and  improve 
the  quality  of  the  milk  to  an  extent  not  fully  explained  by  the 
amounts  of  digestible  matter  or  of  energy  which  they  supply. 
On  the  other  hand,  there  has  been  no  general  agreement  as  to 
what  particular  feeding  stuffs  possess  this  power,  and  scientific 
investigators  have  been  led  to  question  the  existence  of  such 
effects,  particularly  upon  the  composition  of  milk.  A  discus- 
sion of  the  literature  of  the  subject  up  to  1903  by  Lemmermann 
and  Linkh  2  affords  striking  instances  of  the  discrepancies  be- 
tween different  experiments.  The  effects  of  such  feeds  as 
palmnut  meal,  cocoa  meal,  and  cottonseed  meal,  for  example, 
are  reported  by  different  experimenters  as  favorable,  unfavor- 
able or  indifferent. 

1  Landw.  Vers.  Stat.,  62  (1905),  u;   64  (1906),  357;  67  (1907),  253;  71  (1909), 
373;  74  (1911),  163. 

2  Landw.  Jahrb.,  33  (1903),  564. 


524  NUTRITION  OF  FARM  ANIMALS 

Defective  planning  of  experiments  is  doubtless  responsible  for 
much  of  this  confusion.  In  many  instances  the  experimenters  have 
simply  added  the  feed  to  be  tested  to  a  light  basal  ration,  as  in  the 
familiar  experiments  by  G.  Kiihn  l  on  palmnut  meal  so  frequently 
referred  to.  Others,  while  substituting  one  feeding  stuff  for  another, 
have  failed  to  show  that  the  total  amount  of  digestible  matter  sup- 
plied was  unchanged.  In  some  extensive  investigations,  for  instance, 
oil  meals  and  similar  feeds  have  been  interchanged  in  amounts  supply- 
ing equal  quantities  of  protein  without  regard  to  other  ingredients. 
Under  such  conditions  concordant  results  could  not  be  expected,  and 
one  can  but  agree  with  Lemmermann  and  Linkh  that  the  evidence  is 
inconclusive,  while  their  own  experiments,  although  indicating  specific 
effects  for  various  feeding  stuffs,  are  scarcely  more  convincing. 

Similar  negative  evidence  is  afforded  by  the  extensive  feeding 
trials  with  dairy  herds  carried  out  in  Denmark  by  Fjord,  Friis 
and  S torch  and  which  afford  the  basis  for  the  so-called  "  feed 
unit "  or  Scandinavian  system  of  comparing  rations  (702). 
In  these  trials  a  variety  of  feeding  stuffs,  including  many  re- 
puted to  have  specific  effects  on  milk  production,  were  compared 
with  ordinary  farm  grains  and  failed  to  exert  any  material 
influence  on  the  milk  secretion  other  than  what  may  be  plausibly 
explained  by  the  variations  in  the  protein  content  and  the  total 
nutrients  of  the  rations  incident  to  the  experimental  method. 
In  particular,  indications  of  a  specific  effect  on  the  production 
of  milk  fat  are  lacking. 

More  positive  results  have  been  reached,  however,  in  two 
recent  investigations,  viz.,  in  a  series  of  investigations  by  Hansen 
at  the  Agricultural  Academy  Bonn-Poppelsdorf  and  in  a  series 
of  cooperative  experiments  on  palmnut  meal  made  under  the 
auspices  of  the  German  Agricultural  Council. 

619.  Hansen's  experiments.  —  Hansen's  experiments  2  in- 
cluded nine  series  on  63  cows,  extending  over  5  years,  in  which 
the  various  feeding  stuffs  to  be  tested  were  substituted  in  a 
comparison  ration  for  others  which  appeared  to  be  indifferent 
in  this  respect.  Care  was  taken  to  keep  the  total  digestible 
nutrients  in  the  rations,  or  after  the  first  3  years,  the  estimated 
net  energy  values  (starch  values),  unchanged. 

1  Jour.  Landw.,  22  (1874),  178. 

2  Landw.  Jahrb.,  35  (1906),  125 ;  35  Ergzbd.  Bd.  IV,  327 ;  37  (1908),  Ergzbd.  Bd. 
Ill,  171 ;  40  (IQII),  Ergzbd.  Bd.  I,  129. 


MILK  PRODUCTION  525 

The  results  show  distinct  effects  of  certain  feeding  stuffs  on 
the  milk  yield  which  were  apparently  quite  independent  of  the 
supply  of  digestible  nutrients  or  of  energy  values,  or  of  the  pro- 
tein supply,  and  which  were  consistent  when  the  experiments 
were  repeated. 

Hansen  1  distinguishes  three  groups  of  these  feeding  stuffs. 
Those  of  the  first  group,  including  "  maizena  "  (apparently 
gluten  feed),  maize  and  oats,  increase  the  quantity  of  milk  but 
depress  the  percentage  of  fat,  so  that  the  total  yield  of  fat  is  not 
materially  changed.  Those  of  the  second  group,  including 
palmnut  meal,  cocoa  residues,  maize  distillers'  grains,  and  to  a 
less  degree  linseed  and  cottonseed  meal  and  the  legumes,  in- 
crease the  total  yield  of  fat  without  materially  affecting  the 
quantity  of  milk,  so  that  the  percentage  of  fat  in  the  milk  is 
increased.  Those  of  the  third  group,  including  poppy  cake, 
"  false  flax  "  2  cake,  rice  feed  and  to  a  less  degree  sesame  cake, 
diminish  the  yield  of  fat  but  do  not  sensibly  affect  the  quantity 
of  milk,  so  that  the  percentage  of  fat  is  decreased. 

In  a  subsequent  investigation 3  on  substantially  the  same  plan, 
Hansen  has  compared  the  effects  of  palmnut  cake  containing 
respectively  5.55  and  12.42  per  cent  fat  when  fed  in  different 
amounts.  He  concludes  that  the  specific  effect  increases  with 
the  proportion  of  palmnut  cake  in  the  ration  and  with  the  per- 
centage of  fat  contained  in  the  cake.  He  finds  that  to  secure 
significant  results  in  practice,  about  2  pounds  per  1000  pounds 
live  weight  of  fat-rich  cake  and  2^  to  3  pounds  of  the  poorer 
grades  are  necessary.  Different  individual  animals  have  dif- 
ferent degrees  of  susceptibility  to  the  effects  of  palmnut  cake 
but  the  result  can  be  obtained  if  sufficient  is  fed. 

The  principal  criticism  to  be  made  of  Hansen's  experiments 
is  that  the  experimental  periods  were  so  short  —  usually  7  days 
preliminary  and  7  days  for  the  experiment  proper.  It  is  not 
an  unusual  experience  in  dairy  feeding  experiments  to  see  a 
change  of  rations  followed  by  a  temporary  stimulation  of  the 
milk  production  which  is  not  sustained,  and  the  question  natu- 
rally arises  whether  the  "  specific  "  effects  which  seem  to  be 
demonstrated  in  the  first  week  or  two  would  have  continued 
for  a  longer  tune. 

1  Loc.  cit.,  Bd.  40,  pp.  187-188.  *  Camelina  Sativa. 

3  Landw.  Jahrb.,  47  (1914),  30. 


526 


NUTRITION  OF   FARM  ANIMALS 


620.  Cooperative  experiments.  —  The  cooperative  experi- 
ments under  the  auspices  of  the  German  Agricultural  Council 1 
relate  to  the  influence  of  palmnut  cake  or  meal  and  were  made 
according  to  a  common  plan  at  seven  different  institutions  with, 
in  all,  1 86  cows.  The  experimental  periods  covered  about  one 
month  each,  of  which  the  first  5  to  7  days  were  regarded  as  a 
preliminary  feeding.  The  comparison  was  between  4  pounds 
of  palmnut  meal  per  1000  pounds  live  weight  and  an  amount 
of  a  mixture  of  maize  meal  and  peanut  meal  supplying  equal 
protein  and  energy  values  (computed).  After  correcting  for 
the  advance  of  lactation,  the  substitution  of  palmnut  meal  re- 
sulted not  only  in  each  of  the  7  experiments  as  a  whole,  but  with 
nearly  all  the  individual  cows  in  a  distinct  increase  of  the  fat 
production.  The  total  quantity  of  milk  yielded  was  substan- 
tially unaffected,  so  that  the  percentage  of  fat  in  the  milk  was 
increased.  The  average  effects  of  the  palmnut  meal  were  as 
shown  in  the  following  table. 

TABLE  150.  —  EFFECTS  OF  PALMNUT  MEAL  ON  MILK  PRODUCTION 


Bonn    

DAILY  INCREASE  (+) 
OR  DECREASE  (—  )  IN 
YIELD 

PERCENTAGE  OF  FAT  IN 
MILK 

Milk 

Kgs. 

Milk  Fat 
Grams 

On  Palm- 
nut  Meal 

On  Check 
Ration 

—  0.29 
+  0.58 
+  0.28 
+  0.09 
—  0.04 
+  0.06 
+  O.O2 

+  62 
+  48 
+  22 
+  64 
+  15 
+  25 
+  13 

3.58 
3-25 
3-17 
3-51 
3.85 
3-78 
4.21 

3-24 
2.97 

3-05 
3-17 
3.68 

3-51 
4-05 

Danzig 

Griefswald     

Hamburg 

Jena           f 

Friesdorf   
\Veihenstephan 

In  general,  cows  that  were  good  milkers  seemed  more  sus- 
ceptible to  the  effects  of  the  palmnut  meal  than  those  yielding 
smaller  amounts.  It  was  also  observed  that  the  effect  did  not 
immediately  follow  the  change  of  feed  but  developed  gradually, 
reaching  its  maximum  in  the  course  of  one  or  two  weeks,  and 


Berichte  iiber  Landwirtschaft,  Heft  21  and  23. 


MILK  PRODUCTION  527 

continued  for  a  time  after  the  feeding  of  palmnut  meal  was 
discontinued.  This  fact  is  of  particular  interest  in  its  bearing 
upon  the  interpretation  of  Hansen's  results. 

The  evidence  of  these  two  series  of  experiments  seems  to  put 
the  possibility  of  a  "  specific/'  effect  of  certain  feeding  stuffs 
upon  milk  production  beyond  doubt.  They  open  up  an  inter- 
esting field  for  further  investigation,  both  as  regards  the  physio- 
logical explanation  of  the  fact  and  as  to  its  practical  significance. 

621.  Specific  effects  associated  with  fats.  —  In  view  of  what 
is  known  regarding  the  significance  of  certain  fats  (or  of  sub- 
stances associated  with  them)  for  growth  (498),  it  is  of  interest 
to  note  that  these  "  specific  "  effects  on  milk  production  seem 
to  be  associated  to  a  considerable  extent,  although  not  ex- 
clusively,  with   the   fat   consumed.     Morgen's   investigations 
(613)  show  that  the  addition  of  fat  to  his  flavorless  rations  had 
such  a  stimulating  effect  up  to  a  certain  limit.     Many  of  the 
feeding  stuffs  believed  to  exert  such   "  specific  "   effects  are 
relatively  rich  in  fat,  notably  palmnut  meal  for  which  the  result 
seems  best  established.     Moreover  in  the  case  of  the  latter 
material,  as  just  noted,  Hansen  finds  the  influence  most  marked 
with  samples  rich  in  fat.     Whether  these  effects  are  due  to  the 
fat  as  such  or  to  associated  substances,  as  is  believed  to  be  the 
case  in  growth,  is  a  matter  for  future  investigation. 

622.  Influence   on   utilization   of   energy.  —  In   conclusion, 
it  may  not  be  superfluous  to  point  out  that  the  stimulating 
effects  of  feed  on  milk  production  do  not  necessarily  imply  any 
higher  utilization  of  the  feed  energy  supplied.     Certain  feeds 
apparently  "  speed  up  "  the  metabolic  processes  in  the  udder, 
but  whether  the  increased  production  is  effected  with  an  in- 
creased or  a  decreased  efficiency  cannot  be  determined  from 
experiments  of  the  type  thus  far  made.     (Compare  Chapter 
XVII,  §  i,  737,  738.) 

623.  Influence  of  feed  on  composition  of  milk.  —  The  results 
outlined  in  the  last  few  pages  have  an  obvious  bearing  on  the 
much  discussed  question  of  the  effect  of  feeding  on  the  composi- 
tion of  milk.    That  such  an  influence  exists  has  long  been  the 
belief  of  practical  dairymen,  while  the  tendency  of  scientific 
investigation  has  been  on  the  whole  to  throw  doubt  upon  it. 
Some  writers  have  gone  so  far  as  to  practically  deny  that  the 
feeding  has  any  significant  influence  upon  the  composition  of 


528  NUTRITION  OF  FARM   ANIMALS 

the  milk,  while  others,  more  conservative,  have  contented  them- 
selves with  pointing  out  the  conflicting  nature  of  the  evidence. 

624.  Influence  on  percentage  of  fat  in  milk.  —  Since  fat  is 
the  specially  valuable  ingredient  of  milk,  the  discussion  has 
centered  around  this  substance.  An  increase  in  the  percentage 
of  fat  in  the  milk  may  result  from  an  increase  in  the  percentage 
of  total  solids,  i.e.,  a  decrease  in  the  water  content,  as  well  as 
from  a  specific  increase  in  the  fat.  The  conservative  view  on 
this  point  was  thus  summed  up  by  Jordan  in  igoS.1 

"  This  question  has  been  much  discussed  and  much  investi- 
gated from  the  work  of  Klihn  in  1868  down  to  the  present  day. 
Many  experiments  have  been  conducted  for  long  periods  and 
short  periods  in  which  very  moderate  rations  have  been  com- 
pared with  very  large  ones,  highly  nitrogenous  foods  with  those 
of  a  low  protein  content,  dry  with  green  or  succulent  materials, 
and  grains  of  the  same  class  with  one  another,  and,  in  a  great 
majority  of  cases,  the  verdict  has  been  that  '  no  consistent 
relation  appears  to  exist  between  the  quantity  or  character  of 
the  ration  and  the  composition  of  the  milk.'  The  writer  has 
examined  the  results  of  nearly  all  the  important  experiments 
of  this  character  of  which  he  could  find  a  record,  and  in  but  few 
cases  could  he  discover  that  there  was  a  material  increase  or 
decrease  in  the  proportion  of  milk  solids  which  bore  a  logical 
relation  to  variations  in  the  ration.  In  some  cases  a  temporary 
change  appeared  in  the  milk  immediately  after  a  violent  change 
in  the  ration,  but  in  most  instances  of  this  kind  there  was  very 
soon  a  return  to  the  animal's  normal  product.  In  a  small 
proportion  of  experiments,  the  milk  appeared  to  sustain  a  per- 
manent though  not  extensive  modification.  The  weight  of 
testimony  bears  out  the  statement  that  the  quality  of  milk 
cannot  be  changed  at  will  by  the  farmer,  but  is  largely  deter- 
mined by  causes  not  under  his  control,  such  as  breed  and  indi- 
viduality, although  feeding  and  treatment,  especially  the  latter, 
have  more  or  less  influence  upon  the  character  of  the  milk 
secreted." 

Much  of  the  alleged  effect  of  feeding  stuffs  upon  the  com- 
position of  milk  is  associated  with  the  question  of  the  so-called 
"  specific  "  effects  of  feeding  stuffs  (618).  As  was  pointed  out 

1  The  Feeding  of  Animals,  5th  Edition,  The  Macmillan  Co.,  New  York,  1908, 
PP-  317-318. 


MILK  PRODUCTION       ,'.  529 

in  considering  that  question,  both  the  planning  and  execution 
of  many  of  the  older  experiments  were  defective  and  their 
results  must  be  regarded  as  inconclusive.  The  more  recent 
experiments  of  Hansen  and  of  the  German  Agricultural  Coun- 
cil, on  the  other  hand,  as  well  as  the  investigations  of  Morgen, 
Fingerling  and  their  associates  upon  the  influence  of  feed  fat 
and  of  condiments  upon  milk  production,  afford  numerous  ap- 
parently unquestionable  instances  of  an  effect  of  the  ration 
upon  the  fat  content  of  the  milk. 

For  example,  the  experiments  of  the  German  Agricultural 
Council  on  palmnut  meal  (620)  showed  an  average  increase  in 
the  percentage  of  fat  ranging  in  the  different  experiments  from 
4  per  cent  to  n  per  cent,  while  individual  cows  showed  even 
more  striking  differences.  Morgen's  results  on  the  specific 
effect  of  feed  fat  when  added  to  fat-poor  rations  (613)  and  like- 
wise Fingerling 's  results  regarding  the  influence  of  condiments 
(617)  afford  even  more  striking  examples  of  the  same  effect. 
Apparently  it  must  be  admitted  that,  under  some  conditions, 
the  fat  content  of  milk  may  be  distinctly  affected  by  the  feeding 
and  that  this  effect  appears  to  be  associated  with  the  fat  supply 
of  the  ration. 

625.  Influence  on  percentage  of  fat  in  solids.  —  Further- 
more, it  appears  from  such  of  these  latter  experiments  as  in- 
cluded determinations  of  the  total  solids  of  the  milk  that  the 
increase  in  fat  content  was  essentially  a  "  one-sided  "  increase, 
i.e.,  that  the  proportion  of  fat  to  other  solids  in  the  milk  was  in- 
creased. This  was  notably  the  case  in  the  majority  of  experi- 
ments on  fat-poor  rations,  in  which  the  proportion  of  fat  in  the 
milk  solids  was  increased  by  from  12.5  per  cent  to  23.5  per  cent 
by  the  addition  of  fat  to  the  feed.  Similar  although  much  less 
marked  results  were  also  obtained  in  Fingerling's  experiments 
upon  the  influence  of  condiments. 

In  Hansen's  experiments,  too,  the  influence  on  the  fat  content 
of  the  milk  was  due,  in  the  majority  of  instances,  largely  to  an 
increase  or  decrease  of  the  percentage  of  fat  contained  in  the 
milk  solids,  the  increase  or  decrease  over  the  comparison  rations 
being  over  5  per  cent  in  fully  one-third  of  the  experiments, 
while  Lindsey l  has  confirmed  Hansen's  results  as  regards 
cocoa  meal. 

1  Mass.  Expt.  Sta.,  Bui.  155. 
2  M 


530  NUTRITION  OF  FARM  ANIMALS 

It  seems  clear  from  the  foregoing  facts  that  the  proportion  of 
fat  in  the  milk  solids,  as  well  as  the  total  yield  of  fat  and  its  per- 
centage in  the  fresh  milk,  may  be  influenced,  temporarily  at 
least,  by  the  nature  of  the  feed,  and  it  may  be  presumed  that 
some  of  the  results  obtained  on  this  point  in  the  earlier  and  less 
conclusive  experiments  did,  as  a  matter  of  fact,  represent  a  real 
effect  of  this  sort. 

626.  Significance  in  practice.  —  Too  much  stress  must  not, 
however,  be  laid  on  the  physiological  facts  apparently  estab- 
lished by  the  evidence  just  considered.  It  still  remains  true 
that  those  major  differences  in  the  composition  of  milk  from 
different  sources  which  are  of  commercial  importance  are  due 
to  breed  and  individual  differences  in  animals  (564).  As  has 
been  repeatedly  insisted,  the  prime  factor  in  successful  dairy- 
ing is  the  capacity  of  the  animal  as  a  milk  producer.  The 
quality  of  milk  best  suited  to  meet  the  demands  of  a  particular 
market  is  most  easily  and  certainly  secured  by  intelligent 
breeding  and  selection,  while  any  influence  of  the  feed  is 
essentially  a  secondary  factor.  At  the  same  time  the  results 
seem  to  indicate  that  while  feed  is  a  secondary  factor  it  is 
not  altogether  a  negligible  one.  If  it  is  possible  by  suitable 
selection  of  feed  to  permanently  increase  the  fat  yield  to  any 
such  extent  as  has  been  observed  in  short  experiments,  or  if, 
on  the  other  hand,  it  may  be  depressed  by  an  unsuitable  choice 
of  feeding  stuffs,  the  matter  is  one  of  considerable  importance 
and  might  well  be  made  the  subject  of  large  scale  cooperative 
investigations  similar  to  those  of  the  German  Agricultural 
Council  on  palmnut  meal. 


CHAPTER  XIV 
WORK  PRODUCTION 

627.  Prime  purpose  of  excess  feed.  —  Aside  from  reproduc- 
tion, the  prime  purpose  for  which  a  mature  animal  consumes 
feed  in  excess  of  its  maintenance  requirement  is  the  production 
of  the  external  mechanical  work  required  for  its  diverse  ac- 
tivities, either  natural  in  the  wild  animal  or  enforced  in  the 
domesticated  work  animal.  It  is  true  that  more  feed  may  be 
consumed  than  is  required  for  this  purpose  and  that  a  fattening 
of  the  animal  may  result.  The  latter,  however,  is  simply  a 
laying  aside  of  reserve  material  which  may  be  utilized  later 
and,  however  important  economically,  may  be  regarded  as 
physiologically  incidental.  Any  considerable  fattening  of  the 
work  animal  is  not  only  a  diversion  of  energy  from  the  main 
purpose  of  the  feeding  but  constitutes  an  extra  weight  to  be 
carried  by  the  animal,  while  if  too  extensive  it  may  interfere 
with  heart  action  and  respiration. 

Since  horses  or  mules  are  substantially  the  working  animals 
of  the  United  States,  the  following  discussion  will  have  refer- 
ence chiefly  to  these  animals. 


§  i.  THE  PHYSIOLOGY  OF  WORK  PRODUCTION 

Nature  of  muscular  work 

628.  The  muscles.  —  Mechanical  work  is  performed  by  an 
animal  by  means  of  its  muscles  (84,  85),  of  which  there  are  two 
kinds  called,  respectively,  striped,  or  striated,  and  smooth,  or 
non-striated,  muscles  from  the  appearance  of  the  microscopic 
fibers  of  which  they  are  composed.  The  skeletal  muscles,  by 
means  of  which  external  work  is  performed,  are  striated  muscles. 
They  are  also  called  voluntary  muscles  because  they  are  inner- 

S31 


532  NUTRITION  OF  FARM  ANIMALS 

vated  from  the  cerebro-spinal  system  and  are  under  the  con- 
trol of  the  will.  The  muscles  of  the  internal  organs  are  chiefly 
non-striated  muscles,  the  heart  being  the  conspicuous  exception, 
and  are  to  a  very  limited  degree  subject  to  the  will,  being  in- 
nervated from  the  sympathetic  nervous  system.  In  the  study 
of  work  production,  therefore,  we  have  to  do  chiefly  with  the 
phenonena  of  striated  voluntary  muscles. 

The  physiology  of  the  muscle  and  of  muscular  contraction 
is  a  very  complex  subject  and  wide  differences  of  opinion  exist 
regarding  many  aspects  of  it.  All  that  is  attempted  here  is  to 
outline  such  general  features  as  seem  necessary  for  a  proper 
comprehension  of  its  relations  to  nutrition. 

629.  Contraction.* — When    a   suitable    stimulus,    which   in 
the  living  animal  is  usually  a  nerve  stimulus,  is  applied  to  a 
muscle  it  contracts,  that  is,  it  tends  to  grow  shorter  and  thicker. 
This  change  is  brought  about  by  a  shortening  and  thickening  of 
the  individual  fibers  of  which  the  muscle  is  built  up.     A  single 
stimulus,  such,  for  example,  as  that  caused  by  the  making  or 
breaking  of  an  electric  circuit,  gives  rise  to  what  is  known  as 
a  simple  muscular  contraction  or  twitch.     If  such  a  stimulus  is 
repeated  with  sufficient  frequency  it  produces  a  series  of  simple 
contractions  which  fuse  together,  resulting  in  a  state  of  contrac- 
tion which  continues,  subject  to  the  effects  of  fatigue,  as  long 
as  the  stimulus  acts.     This  form  of  muscular  contraction  has 
received  the  name  of  "  tetanus."     In  the  living  animal  the 
ordinary  contractions  of  the  muscles,  brought  about  by  the 
nervous  system,  even  those  that  seem  but  momentary,  are 
essentially  tetanic  in  their  character. 

The  term  contraction  as  used  in  connection  with  the  physi- 
ology of  muscle  does  not,  however,  necessarily  imply  an  actual 
shortening  of  the  muscle.  Contraction  may  either  be  isotonic 
or  isometric.  When  the  muscle  in  contracting  overcomes  a 
constant  resistance,  as,  for  example,  in  raising  a  weight,  the 
contraction  is  said  to  be  isotonic.  When,  on  the  other  hand,  the 
points  of  attachment  of  the  muscle  are  fixed,  evidently  no  work 
can  be  done  in  the  mechanical  sense  but  the  muscle  still  con- 
tracts in  the  physiological  sense,  i.e.,  exerts  a  pull.  Such  a  con- 
traction is  called  an  isometric  contraction. 

630.  Chemical  changes  in  contraction.  —  In  a  muscular  con- 
traction,  either  isotonic  or  isometric,   there  occurs  a  rapid 


WORK  PRODUCTION  533 

katabolism  of  materials  contained  in  the  muscle  or  brought  to 
it  by  the  circulation  together  with  a  corresponding  transfor- 
mation of  their  chemical  energy.  This  katabolism  is  in  effect 
an  oxidation,  yielding  chiefly  carbon  dioxid  and  water,  but  as 
to  the  details  of  the  process,  the  views  of  physiologists  differ. 

Certain  general  features  of  muscular  katabolism  are  fairly  well 
made  out.  First  the  immediate  accompaniment  of  contraction  is 
not  an  oxidation  but  a  rapid,  almost  explosive,  breaking  down  of  a 
substance  or  substances  present  in  the  muscle,  causing  the  produc- 
tion of  carbon  dioxid.  It  has  been  shown,  according  to  Zuntz  and 
Loewy,  that  the  muscle  contains  no  free  oxygen.  Nevertheless,  it 
contracts  instantaneously  when  stimulated,  while  the  effects  upon 
the  blood  supply  follow  later,  circulation  and  respiration  being  stimu- 
lated by  the  carbon  dioxid  and  other  products  formed.  Further- 
more, it  has  been  shown  that,  under  certain  conditions  at  least,  a 
muscle  may  continue  to  contract  and  give  off  carbon  dioxid  in  the 
entire  absence  of  oxygen. 

With  continued  activity  of  the  muscle,  there  is  established  more  or 
less  distinctly  a  state  of  equilibrium  with  the  increased  blood  supply, 
oxygen  being  taken  up  by  the  muscle  and  carbon  dioxid  given  off, 
while,  according  to  a  number  of  experimenters,  the  dextrose  of  the 
blood  also  disappears  during  its  passage  through  the  muscle.  Other 
products  of  muscular  katabolism,  notably  lactic  acid  and  potas- 
sium mono-phosphate  —  the  so-called  fatigue  products  —  tend  to 
accumulate  in  the  muscle  and  diminish  and  finally  suspend  its  ability 
to  respond  to  a  stimulus.  Fatigue  of  the  muscles  usually  results 
from  a  gradual  accumulation  of  these  substances  and  not  from  lack 
of  material  to  be  katabolized. 

631.  Energy  transformations.  —  The  katabolism  of  matter 
which  takes  place  in  muscular  contraction  implies  an  equiva- 
lent conversion  of  chemical  energy  into  kinetic  energy.  The 
energy  thus  transformed  appears  finally  in  the  two  forms  of  heat 
and  visible  motion  (work)  though  the  ratio  between  the  two 
may  vary  widely  under  different  conditions.  As  regards  the 
intermediate  stages  of  this  process,  relatively  little  certain 
knowledge  is  yet  available.  Broadly,  it  may  be  said  that 
there  are  two  possible  general  views.  The  first  of  these  con- 
siders that  the  potential  energy  of  the  material  katabolized  is 
first  converted  into  heat,  and  that  subsequently  a  portion  of 
this  heat  is  converted  into  mechanical  motion.  The  second 


534  NUTRITION  OF  FARM  ANIMALS 

general  view  considers  that  heat  and  work  are  simultaneously 
produced,  a  portion  of  the  energy  taking  one  form  and  a  portion 
the  other.  The  former  view  has  been  supported  by  no  less 
distinguished  an  authority  than  Englemann,  but  nevertheless 
it  has  not  been  generally  accepted  by  physiologists.  In  par- 
ticular, it  is  difficult  to  conceive  of  the  existence  in  a  muscle 
of  sufficient  temperature  differences  to  account  for  its  observed 
efficiency.  In  other  words,  the  muscle  is  not  in  general  re- 
garded as  being  a  heat  engine.  The  prevailing  view,  stated  in 
the  broadest  outline,  is  that  in  the  chemical  changes  conse- 
quent on  a  stimulus,  energy  is  in  part  liberated  as  heat  and  in 
part  expended  in  producing  or  maintaining  tension  of  the  muscle 
fibers.  To  use  a  simple  illustration,  it  is  as  if  by  some  process 
the  elasticity  of  a  cord  supporting  a  weight  were  to  be  sud- 
dently  increased.  The  cord  would  contract  and  the  weight 
would  be  lifted  for  a  certain  distance.  In  isotonic  contraction, 
that  is,  when  the  muscles  are  free  to  shorten,  the  increased  ten- 
sion set  up  does  mechanical  work.  In  isometric  contraction 
this  increased  tension  is  also  finally  converted  into  heat,  as  for 
example  in  the  case  of  muscular  contraction  applied  to  simply 
sustaining  a  weight.  In  this  case  no  work  in  the  mechanical 
sense  is  done,  but  energy  is  expended  in  what  has  sometimes 
been  called  "  static  work."  A  familiar  illustration  of  "  static 
work  "  is  the  muscular  effort  required  in  standing. 

632.  Tonus.  —  In  the  foregoing  paragraphs  it  has  been 
tacitly  assumed  that  before  and  after  a  contraction  the  muscle 
is  absolutely  relaxed.  Such  is  not  normally  the  case.  Even 
in  a  state  of  rest,  so-called,  there  is  a  greater  or  less  degree  of 
tension  of  the  muscles,  especially  during  the  wakening  hours, 
known*  as  tonus  or  tonic  contraction.  In  other  words,  the 
living  muscle  is  slightly  on  the  stretch,  as  is  shown  by  the  fact 
that  it  gapes  open  when  cut  or  shortens  when  its  connections 
with  the  bone  are  severed.  This  tension,  like  the  much  greater 
one  set  up  in  active  contraction,  is  maintained,  in  part  at  least, 
by  a  continual  katabolism  in  the  muscle,  which  respires,  taking 
up  oxygen  and  giving  off  carbon  dioxid.  In  other  words,  the 
"  resting  "  muscle  is  in  a  state  of  slight  isometric  contraction 
and  is  doing  "  static  work."  According  to  the  principles  just 
enunciated,  all  the  energy  transformed  in  such  a  muscle  finally 
takes  the  form  of  heat,  so  that,  as  indicated  in  Chapter  VII 


WORK  PRODUCTION  535 

(348),  muscular  katabolism  is  the  most  important  source  of 
heat  in  the  animal  body.  The  degree  of  tonus  and  conse- 
quently the  rate  of  heat  production  seems  to  vary  at  different 
times  and  in  different  bodily  conditions.  During  profound 
sleep  it  is  much  reduced.  It  is  probably  increased  by  all  con- 
ditions which  favor  the  development  of  a  vigorous  muscular 
system.  What  is  ordinarily  spoken  of  as  a  muscular  contrac- 
tion, therefore,  and  especially  a  tetanic  contraction,  is  in  a  sense 
an  enormous  increase  of  a  condition  already  existing  in  the 
muscle. 

Secondary  effects  of  muscular  exertion 

The  great  increase  of  the  muscular  katabolism  during  the 
performance  of  work  gives  rise  to  important  secondary  effects, 
particularly  upon  the  circulation  and  respiration.  It  is  a 
familiar  fact  that  in  active  exercise  the  heart  action  is  largely 
increased  and  the  breathing  becomes  deeper  and  more  rapid, 
and  that  ordinarily  the  limit  to  muscular  exertion  is  set,  not 
by  the  power  of  the  muscles  themselves  but  by  the  ability  of 
the  heart  and  lungs  to  keep  pace  with  the  demands  upon  them. 

633.  Circulation.  —  The  circulating  blood  is  the  medium  by 
which  oxygen  is  conveyed  to  the  muscles  and  carbon  dioxid 
and  other  products  of  their  katabolism  removed.  The  latter 
function  is  of  special  importance  because  an  accumulation  in 
the  muscle  of  the  products  of  its  own  katabolism  speedily  re- 
duces and  ultimately  suspends  its  power  to  contract.  In  mus- 
cular exercise,  therefore,  an  increase  in  the  rate  of  circulation  is 
essential  to  the  continued  activity  of  the  muscles.  For  ex- 
ample, in  experiments  by  Chauveau  and  Kaufmann  l  the 
ratio  between  the  circulation  in  the  resting  as  compared  with 
the  active  muscle  in  the  living  animal  varied  between  i :  3.35 
and  i :  6.60.  Zuntz  and  Hagemann,2  in  their  investigations 
upon  the  work  of  the  heart,  found  the  average  amount  of  blood 
passing  through  the  heart  of  a  horse  per  minute  to  be  during 
rest  29.16  liters  and  during  work  53.03  liters.  By  this  increase 
in  the  rate  of  circulation  .through  the  muscles  the  carbon  di- 
oxid and  other  injurious  products  of  the  muscular  katabolism 

1  Comptes  rend.,  104,  1126,  1352,  1409. 

2  Landw.  Jahrb.,  27  (1898),  Supp.  Ill,  405. 


536  NUTRITION  OF  FARM  ANIMALS 

are  rapidly  removed  and  an  abundant  supply  of  oxygen  is  en- 
sured. In  fact,  it  is  usually  true  that  during  work  which  is  not 
excessive  the  venous  blood  contains  less  carbon  dioxid  and 
more  oxygen  than  during  rest. 

Since  the  heart  is  a  muscular  organ,  it  is  obvious  that  this 
increase  in  the  circulatory  activity  must  add  materially  to  its 
metabolism.  In  the  performance  of  work,  therefore,  there  is 
an  expenditure  of  matter  and  energy,  not  only  for  the  work  of 
the  skeletal  muscles,  but  likewise  for  the  additional  work  of  the 
heart.  Zuntz  and  Hagemann  in  their  experiments  upon  the 
horse  just  mentioned  compute  that  during  moderate  work  the 
katabolism  due  to  the  work  of  the  heart  amounts  to  3.8  per 
cent  of  the  total  katabolism  of  the  body. 

634.  Respiration.  —  The  greater  activity  of  the  circulation 
consequent  upon  muscular  exertion  would  be  futile  were  not 
provision  made  for  more  efficient  aeration  of  the  blood  in  the 
lungs  through  an  increased  activity  of  the  respiration.  Under 
the  stimulus  of  the  carbon  dioxid  and  other  katabolic  products 
of  muscular  activity  which  enter  the  blood,  the  respiratory  move- 
ments are  increased  in  frequency  or  depth  or  both,  as  described 
in  Chapter  IV  (194),  thus  making  possible  a  more  rapid  gaseous 
exchange  between  the  blood  and  the  air  in  the  lungs.  This 
action  is  usually  so  efficient  that  the  expired  air  during  work 
contains  a  smaller  proportion  of  carbon  dioxid  than  it  does 
during  rest,  notwithstanding  the  fact  that  the  total  quantity 
eliminated  is  much  greater.  Since  respiration,  like  circu- 
lation, is  maintained  by  muscular  action,  it  is  true  in  the  former 
case  as  in  the  latter  that  a  greater  activity  of  the  function  neces- 
sitates a  greater  metabolism  for  that  purpose. 

Effect  of  work  upon  protein  katabolism 

As  already  indicated,  knowledge  of  the  details  of  muscular 
katabolism  is  still  meager.  The  student  of  nutrition,  however, 
is  less  directly  interested  in  these  details  than  he  is  in  knowing 
the  aggregate  effect  of  the  performance  of  work  upon  the  ex- 
penditure of  matter  and  energy  by  the  body  under  varying 
conditions,  since  it  is  this  latter  which  must  be  made  good  by 
the  feed  supply.  Much  effort  has  therefore  been  devoted  to 
studies  of  the  influence  of  muscular  exertion  upon  the  kind  and 


WORK  PRODUCTION  537 

amount  of  material  broken  down  in  the  body  during  work.  It 
will  be  convenient  to  consider  the  effects  of  muscular  work,  first 
upon  the  protein  katabolism  and  second  upon  the  katabolism 
of  non-nitrogenous  material. 

635.  Early  views.  —  Since  the  muscles,  by  means  of  which 
work  is  performed,  consist  largely  of  protein,  it  was  not  un- 
natural for  the  early  physiologists  to  suppose  that  the  sub- 
stance of  the  muscle  itself  was  consumed  and  yielded  the  energy 
for  the  work  done.     This  was  Liebig's  view,  although  it  does 
not  seem  to  have  been  based  upon  any  actual  experimental 
results.     He  taught  that  work  was  performed  at  the  expense 
of  a  katabolism  of  protein   in    the    muscles,   causing  an  in- 
creased excretion  of  nitrogenous  by-products  and  an  increased 
demand  for  protein  in  the  feed,  while  the  carbohydrates  and 
fats  of  the  feed  were  regarded  as  simply  heat  and  fat  producing 
materials. 

636.  Analogy  with  engine.  —  The  analogy  drawn  in  Chapter 
VI  (274-276)  between  the  body  and  an  engine,  however,  might 
of  itself  lead  one  to  question  the  truth  of  this  view.     An  engine 
does  not  do  work  by  burning  up  its  own  substance  but  by  burn- 
ing fuel  material,  and  if  it  is  well  constructed  the  wear  due  to 
the  work  imposed  upon  it  is  comparatively  slight.     It  might 
be  reasonably  expected,  therefore,  that  the  machinery  of  the 
animal  body  would  prove  to  be  at  least  as  perfectly  constructed 
as  an  artificial  machine  and  at  least  equally  capable  of  convert- 
ing the  energy  of  fuel  material  into  work  without  destroying 
the  materials  entering  into  its  own  structure.     That  such  is 
indeed  the  case  under  normal  conditions  was  first  shown  by 
Carl  Voit,  whose  results  have  been  fully  confirmed  by  later 
investigators. 

Voit's  first  investigation l  was  upon  a  dog  alternately  resting 
and  doing  considerable  work  on  a  treadmill  both  when  fasting  and 
upon  a  liberal  meat  diet.  The  results  are  shown  in  the  first  of  the 
two  following  tables,  while  the  second  contains  the  average  results 
of  a  later  series  of  similar  experiments  by  Pettenkofer  and  Voit  2 
on  a  man. 

1  Untersuchungen  iiber  den   Einfluss  des  Kochsalzes,    des  Wassers,  und   der 
Muskelbewegungen  auf  den  Stoffwechsel.  1860.     Summarized  by  E.  v.  Wolff  in 
Die  Ernahrung  der  landw.  Nutzthiere,  pp.  386-388. 

2  Ztschr.  f.  Biol.,  2  (1866),  478. 


538  NUTRITION  OF   FARM  ANIMALS 

TABLE  151.  —  EFFECT  OF  WORK  ON  PROTEIN  KATABOLISM  OF  A  DOG 


NUMBER  OF  EXPERI- 
MENT 

MEAT 
EATEN 

WATER 
DRUNK 

URINE 
EXCRETED 

UREA 
EXCRETED 

Grams 

Grams 

Grams 

Grams 

I 

O 

fRest 

258 

1  86 

14-3 

\Work 

872 

Sl8 

16.6 

[Rest 

123 

145 

11.9 

II        

o 

\  Work 

527 

1  86 

12.3 

[Rest 

125 

143 

10.9 

fRest 

182 

1060 

109.  8 

m         .  . 

I  =^OO 

<  Work 

657 

1330 

117.2 

[Rest 

140 

1081 

109.9 

IV     

1500 

/Work 
\Rest 

412 
63 

1164 
1040 

114.1 
110.6 

TABLE  152.  —  EFFECT  OF  WORK  ON  PROTEIN  KATABOLISM  OF    A  MAN 


NUMBER  OF 
EXPERIMENTS 

UREA  EX- 
CRETED 

Fasting 
Rest       

2 

Grams 
26.5 

Work 

I 

2^  O 

Average  diet 
Rest 

? 

^  6 

Work 

2 

168 

In  the  case  of  the  man,  while  there  was  a  great  increase  in  the 
amount  of  carbon  dioxid  and  water  excreted,  there  was  practically 
no  increase  in  the  excretory  nitrogen.  With  the  dog  fasting  or  on  a 
meat  diet  only,  there  was  in  every  case  a  small  increase  which  Voit 
attributes  to  a  deficiency  of  non-nitrogenous  nutrients  and  not  to  the 
direct  effect  of  muscular  exertion. 

637.  Influence  of  non-nitrogenous  nutrients.  —  While  Voit's 
results  seem  quite  in  harmony  with  present  conceptions  of  the 
animal  organism  as  essentially  a  converter  of  energy,  they 
aroused  considerable  criticism  at  the  time  and  led  to  an  extended 
controversy  as  to  the  source  of  muscular  energy.  The  effect 


WORK  PRODUCTION 


539 


of  work  upon  the  protein  katabolism  was  repeatedly  investi- 
gated under  the  most  varied  conditions  with  results  which  ap- 
peared upon  their  face  to  be  conflicting.  Some  observers  found 
a  marked  increase  in  the  excretion  of  nitrogen  during  or  following 
work,  while  in  other  investigations  no  such  effect  was  apparent. 
The  key  to  these  conflicting  results  seems  to  have  been  first 
discovered  by  Kellner  in  1879  in  experiments  upon  the  work 
horse.1  He  found  that  so  long  as  the  total  amount  of  feed  was 
ample,  variations  in  the  quantity  of  work  performed  were 
without  effect  upon  the  protein  katabolism.  If,  however,  the 
work  was  increased  to  an  amount  sufficient  to  cause  a  falling 
off  in  the  weight  of  the  animal,  thus  indicating  that  the  energy 
supply  was  insufficient,  the  excretion  of  nitrogen  in  the  urine 
increased  promptly.  Furthermore,  it  was  found  that  if  either 
carbohydrates  or  fat  were  added  to  a  ration  which  was  just 
sufficient  to  enable  the  animal  to  perform  a  given  amount  of 
work,  the  demands  upon  the  animal  could  be  correspondingly 
increased  without  causing  any  increase  in  the  protein  katab- 
olism. This  may  be  illustrated  by  the  following  summary  of 
an  experiment  in  which  the  addition  to  the  ration  consisted  of 
starch  and  in  which  the  amount  of  work  performed  is  expressed 
in  the  number  of  revolutions  of  the  sweep  power  dynamometer 
used. 


TABLE  153.  —  EFFECT  OF  STARCH  ON  PROTEIN  KATABOLISM  OF  WORKING 

HORSE 


WORK,  REVO- 

NITROGEN 

LIVE 

DYNAMOMETER 

Digested 

In  Urine 

WEIGHT 

Grams 

Grams 

Kgs. 

T 

300 

121.  1 

107.2 

540.0 

Il-a 

600 

121.  1 

IIO.2 

538.3 

H-b 

Without  starch     .     . 

600 

121.    . 

115.6 

533-1 

III 

500 

121. 

109.4 

532.5 

IV 

400 

121. 

IOQ.6 

530.7 

JTJ      With  starch      .     .     . 

/8oo 
\6oo 

I  2O. 
120. 

IIS-S 

109.6 

5I7.I 
5I5-4 

Landw.  Jahrb.,  8  (1870),  701 ;  9  (1880),  651. 


540  NUTRITION  OF  FARM   ANIMALS 

The  effect  of  even  a  small  excess  of  work  in  increasing  the 
nitrogen  excretion  of  the  horse  was  so  sharp  that  Kellner  even 
attempted  to  determine  how  much  work  could  be  performed  at 
the  expense  of  a  given  weight  of  starch  or  fat  by  increasing  the 
demand  upon  the  animal  up  to  the  point  where  it  just  failed  to 
cause  an  increase  in  the  nitrogen  excretion  and  a  fall  in  live 
weight. 

A  considerable  number  of  more  recent  experiments  have  fully 
confirmed  Kellner's  conclusion  that  a  deficiency  of  non-nitrog- 
enous nutrients  is  the  chief  cause  of  the  increased  protein 
katabolism  which  sometimes  occurs  during  work  and  have  shown 
that  in  the  presence  of  a  sufficient  amount  of  fats  and  especially 
of  carbohydrates  even  severe  work  can  be  performed  without 
increasing  the  nitrogen  excretion.  Indeed,  moderate  work  con- 
tinued for  a  number  of  days  has  in  some  cases  been  accompanied 
by  a  gain  of  nitrogen,  a  fact  apparently  quite  in  accord  with  the 
common  experience  that  the  muscles  are  strengthened  by  ex- 
ercise. It  is  clear  triat  the  body  normally  uses  non-nitrogenous 
materials  as  the  source  of  the  energy  expended  in  muscular  work, 
exactly  as  it  does  in  the  case  of  the  energy  required  for  its  inter- 
nal activities.  Only  when  the  supply  of  non-nitrogenous  materi- 
als is  inadequate  does  it  resort  to  the  katabolism  of  protein  as  a 
source  of  energy  for  external  work,  precisely  as  it  does  during 
fasting  or  on  exclusive  protein  feeding  as  a  source  of  energy  for 
internal  work  (339,  407). 

Effect  of  work  upon  the  katabolism  of  non-nitrogenous  matter 

638.  Gaseous  exchange  increased.  —  In  striking  contrast 
with  the  minimal  effect  of  work  upon  the  excretion  of  nitrogen 
is  its  very  marked  effect  in  increasing  the  consumption  of  oxygen 
and  the  excretion  of  carbon  dioxid  and  water.  This  increase 
is  too  obvious  from  common  experience  and  too  well  estab- 
lished scientifically  to  require  more  than  an  illustration.  The 
fact  of  such  an  increase  was  shown  in  the  researches  of  Lavoisier 
and  confirmed  by  the  earlier  experimenters  in  this  field,  such 
as  Scharling  in  1843,  Him  in  1857  and  especially  Smith  in  1859. 
The  investigations  of  Pettenkofer  and  Voit  in  1866,  however, 
appear  to  have  been  the  first  to  be  executed  according  to  modern 
methods.  Their  results  regarding  the  influence  of  work  upon 


WORK  PRODUCTION 


541 


the  protein  katabolism  have  already  been  cited  (636)  but  may 
be  repeated  in  connection  with  those  obtained  with  the  aid  of 
the  respiration  apparatus. 

TABLE  154. — INFLUENCE  OF  WORK  ON  GASEOUS  EXCHANGE  OF  MAN 


NUMBER 
OF  Ex- 

UREA 
Ex- 

CARBON 
DIOXID 

WATER  EXCRETED 

OXYGEN 
TAKEN 

MENTS 

CRETED 

EXCRETED 

In  Urine 

Evapo- 
rated 

UP 

Fasting 

Grams 

Grams 

Grams 

Grams 

Grams 

Rest       .... 

2 

26.5 

716 

1006 

821 

762 

Work     .... 

I 

25.0 

1187 

746 

1777 

1072 

Average  diet 

Rest       .... 

3 

33-6 

928 

1218 

931 

832 

Work     .... 

2 

36.8 

1209 

H55 

1727 

981 

639.  Effects  are  immediate.  —  Experiment  confirms  the  com- 
mon observation  that  the  increased  pulmonary  exchange  conse- 
quent upon  muscular  exertion  begins  almost  immediately, 
reaches  its  maximum  in  a  very  short  time  and  disappears 
promptly  when  the  work  ceases.  This  is  especially  true  of  the 
absorption  of  oxygen,  of  which  no  considerable  amount  ap- 
pears to  be  stored  up  in  the  body  in  the  free  state.  In  the  case 
of  the  excretion  of  carbon  dioxid,  more  or  less  of  this  gas  can 
be  held  in  solution  in  the  blood  and  lymph  and  there  is  conse- 
quently some  slight  lag  in  its  excretion. 

In  view  of  this  prompt  adjustment  of  the  respiration  to  the 
amount  of  work,  determinations  of  the  pulmonary  exchange  by 
some  one  of  the  forms  of  respiration  apparatus  described  in 
Chapter  VI  (297-299)  are  especially  useful  in  studying  the  effects 
of  work  upon  the  katabolism.  The  use  of  this  method  renders 
it  possible  to  compare  the  gaseous  exchange  during  periods  of 
work  with  that  of  the  same  animal  at  rest  and  thus  to  deter- 
mine very  sharply  the  additional  oxygen  consumption  and 
carbon  dioxid  excretion  caused  by  a  measured  amount  of 
work.  The  comparative  simplicity  of  the  apparatus  required, 
the  ease  with  which  the  respiratory  changes  can  be  followed  in 
short  periods,  and  the  fact  that  both  oxygen  and  carbon  dioxid 


542  NUTRITION  OF  FARM   ANIMALS 

can  be  determined,  have  led  to  the  extensive  use  of  this  method 
for  investigations  upon  work  production. 

640.  Nature    of    non-nitrogenous    material    katabolized.  — 
Since  under  normal  conditions  muscular  exertion  does  not  in- 
crease the  protein  katabolism,  it  follows  that  the  substances 
oxidized  for  the  performance  of  work  must  be  substantially 
either  carbohydrates  or  fats.     If  the  former,  each  volume  of 
carbon  dioxid  given  off  will  correspond  to  an  equal  volume  of 
oxygen  taken  up ;    that  is,  the  respiratory  quotient  (296)  will 
be  i.o.     On  the 'other  hand,  if  the  material  oxidized  consists 
solely  of  fat,  the  respiratory  quotient  will  be    approximately 
0.7,  while  if  both  are  being  consumed,  it  will  have  an  intermediate 
value.     Moreover,  it  is  comparatively  simple  to  calculate  from 
the  respiratory  quotient  the  proportions  in  which  the  two  are 
being  katabolized.     Investigations  of  this  sort  show  that  the 
proportions  of  fat  and  carbohydrates  katabolized  for  the  per- 
formance of  work  may  vary  within  wide  limits,  both  groups 
being  readily  available  as  sources  of  energy. 

Sources  of  energy  for  muscular  work 

641.  Proteins    vs.    non-nitrogenous    matter.  —  Liebig's    as- 
sumption (635)   of   an  increase  of    the  protein  katabolism  in 
muscular  contraction  implied  that  the  proteins  were  the  source 
of  the  energy  manifested,  and  this  view  prevailed  for  many  years. 
When  Voit,  in  1860,  showed  (636)  that  muscular  exertion  is  not 
necessarily  accompanied  by  any  material  increase  in  the  protein 
katabolism,  the  inference  seemed  unavoidable  that  non-nitrog- 
enous materials  were  the    main  sources  of    muscular  energy. 
This  conclusion,  however,  was  too  radical  to  be  at  once  ac- 
cepted in  opposition  to  Liebig's  authority  and  numerous  in- 
genious, but  not  always  convincing,  hypotheses  were  advanced  to 
explain  the  observed  phenomena  on  the  assumption  that  the 
proteins  were,  nevertheless,  the  source  of  the  energy  expended. 

642.  Fick  and  Wislicenus'  experiment.  —  The  first  attempt, 
however,  at  a  quantitative  comparison  of  the  work  performed 
with  the  energy  available  from  the  protein  katabolized  during 
its  performance  was  the  famous  experiment  of  Fick  and  Wis- 
licenus 1  in  1866.     These  observers  made  an  ascent  of  the  Faul- 

1  Vrtljschr.  Naturf.  Gesell.  Zurich,  10,  317. 


WORK  PRODUCTION  543 

horn,  a  Swiss  mountain  6418  feet  high,  after  having  abstained 
from  nitrogenous  food  for  17  hours,  and  found  that  the  amount 
of  protein  katabolized  during  the  six  hours  occupied  by  the 
ascent  and  the  seven  succeeding  hours  of  rest,  as  measured  by 
the  urea  excreted,  was  insufficient,  according  to  their  com- 
putations, to  account  for  more  than  about  one- third  of  the  energy 
required  to  lift  their  bodies  to  the  height  of  the  mountain,  mak- 
ing no  allowance  for  the  work  of  the  internal  organs  nor  for 
those  muscular  exertions  which  did  not  contribute  directly  to 
the  work  done.  They  observed  no  considerable  increase  in 
the  urinary  nitrogen  over  that  excreted  before  the  ascent. 

643.  Protein  insufficient  as  source  of  energy.  — It  is  true 
(637)  that  with  an  insufficient  supply  of  non-nitrogenous  ma- 
terials in  the  feed  muscular  exertion  may  lead  to  an  increase  in 
the  protein  katabolism,  but  in  the  many  comparisons  which  have 
been  made  since  the  time  of  Fick  and  Wislicenus  by  far  more 
refined  methods  than  were  available  to  them,  this  increase  has 
been  shown  to  be  entirely  inadequate  to  furnish  the  energy  for 
the  work  performed.     Moreover,  even  the  supposition  that  the 
energy  of  the  total  protein  katabolized  was  all  applied  to  work 
production  usually  fails  to  account  for  the  energy  expended. 

The  facts,  then,  first,  that  the  chief,  and  often  the  only,  effect 
of  muscular  work  is  to  increase  the  katabolism  of  non-nitrog- 
enous material;  second,  that  even  the  total  protein  katab- 
olism is  in  most  cases  insufficient  to  supply  the  energy  ex- 
pended in  work ;  and  third,  that,  as  Kellner  (637)  has  shown, 
the  addition  of  non-nitrogenous  nutrients  to  the  ration  enables 
more  work  to  be  done ;  demonstrate  beyond  cavil  that  under 
ordinary  conditions  of  nutrition  it  is  the  non-nitrogenous  in- 
gredients of  the  body  and  of  the  feed  which  supply  most  or  all 
of  the  energy  expended  in  the  performance  of  work. 

644.  Functions    of    proteins.  —  The    foregoing    statements 
should  not  be  understood  as  an  assertion  that  the  proteins 
play  no  part  in  the  production  of  muscular  work.     In  the  first 
place,  their  katabolism  furnishes  a  considerable  amount  of  non- 
nitrogenous  products  (229, 233)  and  that  these  products  are  avail- 
able to  supply  energy  for  work  has  been  strikingly  shown  by 
Pfluger.     He  maintained  a  dog  for  about  nine  months  on  an 
exclusive  diet  of  almost  fat-free  meat  and  showed  that  on  this 
diet  the  animal  was  capable  of  performing  large  amounts  of 


544  NUTRITION  OF  FARM  ANIMALS 

work.  Aside  from  the  small  quantities  of  fat  and  glycogen  con- 
tained in  the  meat  the  energy  for  work  under  these  conditions 
could  have  been  derived  only  from  the  proteins  or  their  cleavage 
products.  These  results  show  clearly  that  protein  may  be  used 
to  a  large  extent  as  a  source  of  muscular  energy,  but  it  is  never- 
theless true  that  under  ordinary  conditions,  and  particularly 
with  farm  animals,  the  main  supply  of  energy  is,  as  already 
stated,  through  the  non-nitrogenous  ingredients  of  the  feed. 

It  is  by  no  means  impossible,  however,  that  a  certain  amount 
of  protein  katabolism  may  be  necessary  in  a  muscular  contrac- 
tion. Such  a  contraction  is  a  function  of  the  protoplasm  of 
the  muscle  fibers  and  it  is  conceivable  that  a  portion  of  the 
energy  arising  from  the  katabolism  of  the  proteins  and  nucleo- 
proteins  of  the  muscle  and  ordinarily  appearing  as  heat  in  the 
resting  muscle  may  be  switched  off,  so  to  speak,  to  aid  in  pro- 
ducing the  contraction.  In  other  words,  it  is  possible  that  a 
certain  level  of  protein  metabolism  may  be  necessary  in  order 
to  maintain  the  most  favorable  conditions  for  transforming 
the  potential  energy  of  non-nitrogenous  materials  into  work.1 
Such  a  fact  would,  of  course,  have  an  important  bearing  upon 
the  amount  of  protein  required  for  a  working  animal,  but  at  pres- 
ent the  matter  belongs  in  the  realm  of  speculation. 


§  2.    THE  EFFICIENCY  OF  THE  BODY  AS  A  MOTOR 

General  results 

646.   Body   substance  is  immediate  source   of   energy.  — 

While  the  energy  expended  in  work  production  is  of  course  de- 
rived ultimately  from  the  feed  consumed,  its  immediate  source, 
as  stated  in  §i  (630),  is  the  katabolism  of  body  substance,  and 
an  animal  may  perform  a  considerable  amount  of  labor  in  the 
fasting  state  at  the  expense  of  stored-up  material.  It  will  aid 
in  the  discussion  of  the  somewhat  complicated  question  of  the 
efficiency  of  the  animal  as  a  prime  motor  to  consider  first  the 
efficiency  with  which  the  body  utilizes  this  stored-up  energy, 
i.e.,  to  inquire  what  percentage  of  the  total  energy  of  the  body 
material  katabolized  for  work  production  is  recovered  in  the 

1  Compare  Armsby,  Principles  of  Animal  Nutrition,  pp.  207-209. 


WORK  PRODUCTION  545 

work  done,  deferring  to  the  following  section  a  study  of  the 
efficiency  of  the  animal  as  a  converter  of  feed  energy  into  use- 
ful work  and  of  the  feed  requirements  of  work  animals. 

646.  Mechanical  efficiency  of  muscle.  —  A  muscle  may  be 
regarded  as  a  machine  for  the  conversion  of  chemical  energy 
into  mechanical  work  and  one  may,  therefore,  speak  of  its 
efficiency  in  somewhat  the  same  sense  as  of  that  of  a  steam 
engine  or  an  electric  motor.     By  efficiency  in  this  sense  is  meant 
the  proportion  of  the  total  energy  mobilized  during  a  contrac- 
tion which  is  recovered  in  the  work  done.     Thus  if  an  isolated 
muscle  lifts  a  weight  of  ten  grams  through  one  centimeter,  it 
does    10    gram    centimeters    of    work,    equivalent    (308)    to 
0.2344  X  io~4  gram  calories.     If  the  increased  katabolism  caused 
in  the  muscle  by  its  contraction  were  shown  to  be  0.4688  X  io~4 
gram     calories,    the    efficiency    of     the    muscle    would    be 
0.2344  -r-  0.4688  =  50  per  cent,  that  is,  50  per  cent  of  the  total 
energy  mobilized  would  be  recovered  as  mechanical  work. 

Much  experimental  work  has  been  devoted  to  the  study  of 
the  single  muscle  as  a  machine.  The  subject  is  a  complicated 
one,  and  unanimity  of  views  upon  it,  especially  as  to  the  mecha- 
nism of  muscular  contraction,  has  by  no  means  been  reached. 
As  regards  the  efficiency  of  the  muscle  as  a  converter  of  energy, 
however,  one  fact  is  perfectly  well  established,  viz.,  that  it 
varies  within  quite  wide  limits,  depending  especially  upon  the 
load  as  related  to  the  capacity  of  the  muscle  and  upon  the  de- 
gree of  shortening. 

647.  Mechanical  efficiency  of  the  body  as  a  whole.  —  If  the 
amount  of  energy  mobilized  in  each  muscle  concerned  in  the 
performance  of  a  certain  form  of  work  were  known,  it  is  con- 
ceivable that,  assuming  each  muscle  to  act  with  its  maximum 
efficiency,  an  average  theoretical  efficiency  might  be  computed 
for  the  whole  group  of  muscles.     The  conditions  for  the  max- 
imum efficiency  of  a  muscle,  however,  seldom  or  never  obtain 
in   the   working   animal,  and   consequently  this  hypothetical 
efficiency  is  not  attained.     Of    its  many  muscles,  some  serve 
largely  or  wholly    to    maintain  the    relative  positions  of    the 
different  parts  of  the  body,  i.e.,  their  contractions  are  isometric 
(629)  and  consequently  have  an  efficiency  approaching  zero. 
Others  contract  to  a  varying  extent  and  under  loads  less  than 
the  maximum.     Some  muscles,  owing  to  their  anatomical  re- 

2  N 


546  NUTRITION  OF  FARM  ANIMALS 

lations,  work  at  a  less  mechanical  advantage  than  others,  while 
the  extent  to  which  a  group  of  muscles  is  called  into  action  will 
vary  with  the  nature  of  the  work.  Moreover,  the  performance 
of  labor  by  an  animal  sets  up  various  secondary  activities, 
notably  of  the  circulatory  and  respiratory  organs  (633,  634), 
which  consume  their  share  of  energy  and  yet  do  not  contribute  di- 
rectly to  the  performance  of  the  work,  and  the  extent  of  these 
secondary  activities  varies  with  the  nature  and  the  severity  of 
the  work.  Some  of  these  sources  of  loss  of  energy  are  anal- 
ogous to  the  radiation  losses  from  the  cylinder  of  a  heat  engine, 
while  others  are  comparable  with  the  internal  resistances  of  the 
engine  itself. 

Determinations  of  the  efficiency  of  the  isolated  muscle,  there- 
fore, afford  no  adequate  means  of  estimating  the  efficiency  of 
the  body  as  a  whole  and  the  latter  must  be  determined  by  di- 
rect experiment.  Such  a  determination  is  made  by  causing 
the  animal  to  perform  a  measured  amount  of  work  under  con- 
ditions which  also  permit  the  measurement,  either  directly  as 
heat  or  by  the  methods  of  indirect  calorimetry  described  in 
Chapter  VI,  of  the  total  body  energy  metabolized. 

Thus  in  experiments  by  Benedict  and  Cathcart l  upon  a  man 
riding  a  bicycle  ergometer,  the  subject  breathed  through  the 
mouthpiece  of  a  Benedict  universal  respiration  apparatus 
(298),  by  means  of  which  the  oxygen  consumption  and  the  car- 
bon dioxid  elimination  could  be  determined.  From  these 
data  the  amount  of  energy  metabolized  in  the  body  was  com- 
puted and  compared  with  the  amount  of  mechanical  work  done 
as  measured  by  the  ergometer.  For  example,  in  one  of  these 
tests  the  energy  output  per  minute  as  computed  from  the  res- 
piratory exchange  was  6.32  Cals.,  while  the  mechanical  work 
done  per  minute  was  equivalent  to  1.02  Cals.  In  other  words, 
i. 02  -f-  6.32  =  16.1  per  cent  of  the  total  energy  output  was 
recovered  as  useful  work,  the  remainder  taking  the  form  of 
heat. 

648.  Gross  and  net  efficiency.  —  Comparisons  like  that  of 
the  preceding  paragraph  give  what  is  called  the  gross  efficiency 
of  the  body,  i.e.,  they  show  what  proportion  of  the  total  energy 
metabolized  during  work  is  recovered  in  the  useful  work  done. 
It  is  analogous  to  the  efficiency  of  an  engine  as  computed  from 

1  Muscular  Work;  Carnegie  Inst.  of  Washington,  Publication  No.  187  (1913). 


WORK  PRODUCTION  547 

a  comparison  of  the  brake  horse  power  with  the  steam  con- 
sumption. 

But  the  body  katabolizes  matter  and  liberates  energy  for 
other  purposes  than  the  performance  of  external  work,  —  i.e.,  it 
has  a  maintenance  requirement  for  the  support  of  its  internal 
work  (341,  342)  analogous  in  some  respects  to  the  energy  re- 
quired to  run  an  engine  without  load.  The  subject  of  Benedict 
and  Cathcart's  experiment  produced  during  rest  (lying  on  a 
couch)  1.09  Cals.  of  heat  per  minute.  If  this  maintenance  re- 
quirement be  subtracted  from  the  total  energy  output  during 
work  there  is  left  5.23  Cals.,  as  the  additional  energy  output 
required  for  the  performance  of  the  1.02  Cals.  of  measured  exter- 
nal work.  %  Computed  in  this  way  an  efficiency  of  1.02  -f-  5.23 
=  19.5  per  cent  results.  This  has  been  called  the  net  efficiency. 
It  shows  the  utilization  of  that  portion  of  the  energy  output 
which  is  expended  in  the  physiological  processes  required  for 
the  production  of  external  work  as  distinct  from  the  various 
forms  of  internal  work  included  in  the  maintenance  requirement. 
In  computing  the  net  efficiency  in  this  way  difficulty  arises  in 
deciding  upon  the  proper  deduction  to  be  made.  Thus  in  an 
experiment  like  that  just  cited,  one  may  subtract  from  the 
total  energy  output  of  the  body  during  work,  not  only  the 
energy  expenditure  for  maintenance  during  rest  but  likewise 
that  caused  by  sitting  on  the  ergometer  and  causing  it  to  rotate 
without  load,  and  the  remainder  may  be  regarded  as  the  energy 
metabolized  for  the  performance  of  the  useful  work.  The 
total  output  of  energy  being  6.32  Cals.  per  minute  during  the 
work,  it  was  determined  that  the  same  subject  metabolized  1.13 
Cals.  more  energy  per  minute  when  riding  without  load  than 
when  at  rest.  The  added  load  in  the  work  experiment,  there- 
fore, required  the  expenditure  of  6.32  —  (1.09  -f-  1.13)  =  4.10 
Cals.  per  minute  for  the  performance  of  1.02  Cals.  of 
work,  from  which  an  efficiency  of  24.9  per  cent  may  be  com- 
puted. Similarly,  in  experiments  with  the  work  horse  one  may 
subtract  the  energy  expended  during  horizontal  locomotion  in- 
stead of  that  metabolized  during  rest  and  compare  the  remainder 
with  the  useful  work  done.1 

1  For  a  discussion  of  the  various  base  lines  for  the  computation  of  efficiency, 
compare  Benedict  and  Cathcart's  publication  already  cited,  pp.  112-136,  and  also 
Reach,  Biochem.  Ztschr.,  14  (1908),  430;  Landw.  Jahrb.,  37  (1908),  1053. 


548  NUTRITION  OF  FARM  ANIMALS 

This  method  of  computation  is  unlike  any  usually  employed  by 
the  engineer,  and  Schreber  1  has  criticized  it  severely.  The  engineer 
is  accustomed  to  estimate  the  losses  due  to  the  internal  resistance  of 
an  engine  by  a  comparison  of  brake  horse  power  and  indicated  horse 
power.  No  method  exists,  however,  for  determining  the  indicated 
horse  power  of  the  animate  motor,  if  indeed  it  permits  of  any  cor- 
responding conception,  and  only  the  method  of  comparison  just  out- 
lined is  available.  It  is  as  if  the  engineer  had  no  indicator  and  esti- 
mated the  efficiency  of  his  engine  by  deducting  from  the  total  steam 
consumption  that  required  to  run  the  engine  empty  and  compared 
the  remainder  with  the  external  work  done.  The  internal  work  of 
the  animal,  however,  like  that  of  the  engine,  is  largely  mechanical. 
If,  on  the  basis  of  Zuntz's  computation  of  the  efficiency  in  locomo- 
tion (652),  it  may  be  assumed  that  this  internal  work  is  performed 
with  approximately  the  same  efficiency  as  the  external  work,  then 
the  net  efficiency  of  the  animal  will  be  somewhat  analogous  to  the 
efficiency  of  the  steam  in  the  cylinder  of  the  engine. 

649.  Gross  efficiency  variable.  —  It  should  be  observed  that 
while  the  net  efficiency  may  be  regarded  as  .substantially  con- 
stant under  a  considerable  variety  of  conditions,  the  gross  effi- 
ciency will  vary  with  the  ratio  of  work  done  (load)  to  main- 
tenance requirements.  Thus  if  Benedict  and  Cathcart's 
subject  had  done  only  half  as  much  work  per  minute  with  the 
same  net  efficiency,  his  gross  efficiency  would  have  been  only 
13.7  per  cent  instead  of  16.1  per  cent. 

Total  energy  expended  per  minute. 

For  mechanical  work,  0.51  Cal.  -r-  0.195  =    2-62  Cals. 

For  maintenance  1.09  Cals. 

Total  3.71  Cals. 
Recovered  in  work  done  0.51  Cals. 

Gross  efficiency  13.7  per  cent 

Up  to  the  point  at  which  the  net  efficiency  begins  to  be  affected, 
the  gross  efficiency  will  increase  with  increasing  load  as  Bene- 
dict and  Cathcart  show  experimentally  to  be  the  case.  This 
influence  of  the  maintenance  requirement  upon  the  computa- 
tion of  the  utilization  of  energy  is  identical  with  that  to  which 
attention  has  already  been  called  in  connection  with  the  utili- 
zation for  material  products.  If  the  useful  work  performed 

1  Arch.  Physiol.  (Pfliiger),  159  (1914),  276, 


WORK  PRODUCTION  549 

be  reduced  to  zero,  as  for  example  in  horizontal  locomotion, 
the  gross  efficiency  of  course  also  becomes  zero. 

650.  Efficiency  per  day.  —  The  figures  for  either  gross  or 
net  efficiency  show  the  efficiency  for  the  time  during  which  the 
work  is  being  done.  Since,  however,  it  is  not  practicable  to  stop 
the  animal  machine  when  the  demand  for -work  ceases,  the 
efficiency  for  the  entire  24  hours,  i.e.,  the  degree  to  which  the 
body  energy  is  utilized  in  practice,  will  evidently  vary  with 
the  number  of  hours  work  done  per  day.  Thus  if  Benedict  and 
Cathcart's  subject  had  been  able  to  work  8  hours  per  day  at 
the  same  rate  as  in  the  experiment  just  cited,  his  gross  efficiency 
for  the  24  hours  would  have  been  as  follows :  — 

Energy  expended 

480  minutes  work  @  6.32  Cals.  =  3034  Cals. 

960  minutes  rest  @  1.09  Cals.    =  1046  Cals. 

4080  Cals. 
Work  done 

480  minutes  @  1.02  Cals.  =  490  Cals. 

Efficiency  per  day  12.01  per  cent 

On  the  other  hand,  if  he  had  worked  only  one  hour  per  day, 
it  may  be  presumed  that  both  the  net  and  gross  efficiency  of  the 
work  production  during  the  hour  of  work  would  have  been 
substantially  the  same  but  the  efficiency  for  the  24  hours  would 
have  been  much  lower,  viz., 

Energy  expended 

60  minutes  work  @  6.32  Cals.  =379  Cals. 
1380  minutes  rest  @  1.09  Cals.     =  1504  Cals. 

1883  Cals. 
Work  done 

60  minutes  work  @  1.02  Cals.  =    61  Cals. 
Efficiency  per  day  3.24  per  cent 

In  discussions  of  the  efficiency  of  a  man  or  an  animal  as  a 
motor,  a,nd  particularly  in  comparisons  with  artificial  motors, 
it  is  essential  to  distinguish  clearly  whether  the  net,  or  the  gross 
efficiency  is  meant  and  likewise  to  base  the  comparisons  upon 
the  performance  per  day.  Since  the  net  is  apparently  less 
affected  than  the  gross  efficiency  by  variations  in  the  intensity 
and  duration  of  the  work,  it  appears  to  be  the  most  logical 


550  NUTRITION  OF   FARM   ANIMALS 

method  of  comparison  in  the  case  of  the  animal  as  well  as  being 
the  most  convenient  in  practice. 

651.  Analysis  of  total  work.  —  A  quadruped  performs  work 
by  means  of  locomotion,  with  or  without  draft,  either  horizon- 
tally or  on  an  inclined  plane.     The  work  which  it  performs 
may  therefore  be  subdivided  into  work  of  locomotion,  work  of 
draft  and  work  of  ascent  and  the  efficiency  for  each  form  com- 
puted separately.     The  same  is  of  course  true  of  man,  but  in 
addition  other  forms  of  work,  such  as  turning  a  crank  with 
the  hands  or  with  the  feet  (stationary  bicycle)   or  lifting  a 
weight  directly  may  be  performed.     The  method  of  analyzing 
the  work  of  a  quadruped  has  been  worked  out  especially  by 
Zuntz  and  may  be  conveniently  illustrated  from  Zuntz  and 
Hagemann's  investigations  on  the  work  horse.1     The  methods 
of  indirect  calorimetry  were  used,  carbon  dioxid  production 
and  oxygen  consumption  being  determined  with  the  Zuntz  ap- 
paratus (279)  and  the  corresponding  energy  output  calculated. 
The  work  was  done  upon  a  special  tread-power  located  in  the 
open  air,  and  during  the  rest  experiments  the  animal  likewise 
stood  in  the  tread  power.     The  inclination  of  the  platform  of 
the  power  could  be  varied,  and  it  could  also  be  driven  by  a  steam 
engine,  so  that  by  setting  it  horizontal  the  work  performed  by 
the  animal  was  reduced  to  that  of  locomotion  alone.     The  dis- 
tance traveled  was  measured  by  a  revolution  counter  and  in  the 
experiments  on  draft  the  animal  pulled  against  a  dynamometer. 
The  apparatus  used  is  illustrated  in  Chapter  VI,  Fig.  33  (313). 

652.  Horizontal  locomotion.  —  This  is  an  important  factor 
in  work  production,  since  it  requires  the  expenditure  of  con- 
siderable energy  in  successive  liftings  of  the  body  at  each  step 
and  the  overcoming  of  internal  resistances.     The  energy  thus 
expended  does  not  ultimately  produce  any  work  in  the  me- 
chanical sense,  but  all  appears  as  heat.     The  work  of  locomotion, 
therefore,  is  in  a  sense  not  useful  work  although  necessarily  in- 
cident to  the  performance  of  the  work. 

If  the  tread  power  be  set  horizontal  and  driven  by  a  motor, 
the  total  energy  output  by  the  subject  will  measure  what  may 
be  called,  by  analogy  with  the  gross  efficiency  (648),  the  gross 
expenditure  in  locomotion.  Subtracting  the  energy  output 
during  rest  (standing)  from  the  total  output  during  locomotion 

iLandw.  Jahrb.,  18  (1889),  i;  23  (1894),  125;  27,  Ergzbd.  Ill,  (1898). 


WORK  PRODUCTION  551 

shows  of  course  the  expenditure  in  the  latter  exclusive  of  that 
required  to  maintain  the  body  upright  (work  of  standing), 
or  what  may  be  called  the  net  expenditure. 

On  the  average  of  thirty-five  trials  upon  locomotion  at  a  walk, 
Zuntz  and  Hagemann  found  the  net  expenditure  of  energy  by 
the  horse  per  meter  of  horizontal  locomotion  (after  correcting 
in  the  manner  described  in  the  next  paragraph  for  the  small 
amount  of  work  of  ascent  due  to  the  fact  that  the  tread  power  was 
not  exactly  horizontal)  to  be  as  follows  per  kilogram  of  weight : 

At  a  speed  of  78  meters  per  minute  .  .  .  3256  gram  calories 
At  a  speed  of  90.16  meters  per  minute  .  .  .  3666  gram  calories 
At  a  speed  of  98.11  meters  per  minute  .  .  .  3929  gram  calories 

The  actual  amount  of  mechanical  work  done  in  horizontal 
locomotion  and  converted  into  heat  cannot  be  measured  di- 
rectly. Zuntz  and  Hagemann,  however,  have  computed  it  by 
means  of  a  formula  proposed  by  Kellner  1  and  by  comparison 
with  the  figures  just  given,  compute  a  net  efficiency  of  about 
35  per  cent. 

653.  Work  of  ascent.  —  The  animal  may  also  perform  work 
by  drawing  or  carrying  a  load  up  a  hill.  Taking  the  simpler 
case  of  carrying  a  load,  the  total  output  of  energy  would  be 
expended  for  three  purposes,  viz.,  maintenance  (resting  value), 
locomotion,  and  lifting  the  weight  of  the  load  plus  body  in  op- 
position to  gravity.  Zuntz  separates  the  two  latter  factors  from 
each  other  by  a  comparison  of  two  experiments  in  which  the  ratio 
of  distance  traveled  to  ascent,  i.e.,  the  angle  of  ascent,  differs. 

Thus  in  the  thirty-five  trials  with  nearly  horizontal  locomo- 
tion the  average  energy  output  per  kilogram  of  live  weight,  after 
deducting  the  maintenance  requirement,  was  0.4035  gram  calo- 
ries per  meter  traveled.  During  the  same  time,  however,  the  body 
was  lifted  through  0.4395  centimeters,  equivalent  to  0.004395 
kilogram  meters  of  work  of  ascent  per  kilogram  of  live  weight. 
In  thirteen  experiments  on  ascending  a  moderate  grade,  the 
average  energy  expended  in  excess  of  maintenance  per  kilogram 
live  weight  was  1.0795  gram  calories  per  meter  traveled,  while 
the  work  of  ascent  was  0.107041  kilogram  meters  per  kilogram. 
Letting  x  equal  the  energy  per  kilogram  required  for  one  meter 
of  horizontal  locomotion  and  y  the  energy  required  for  the 

1  Landw.  Jahrb.,  9  (1880),  658. 


552  NUTRITION  OF  FARM  ANIMALS 

performance  of  one  kilogram  meter  of  work  of  ascent,  the  two 
following  equations  may  be  formulated  :  — 


x  +  0.004395  y  =  0-4035 

x  +  0.107041  y  =  1.0795  cals. 

From  these  equations  the  values  of  x  and  y  can  be  computed 
to  be  as  follows  :  — 

x  =  0.3746  cals.     y  =  6.5856  cals. 

Since  one  kilogram  meter  is  equivalent  to  2.344  cals.,  it  fol- 
lows that  the  net  efficiency  in  the  work  of  ascent  was 
2.344  -T-  6.5856  =  35.73  per  cent.  In  effect,  the  net  efficiency  in 
work  of  ascent  is  computed  by  deducting  from  the  total  energy 
output  the  amounts  expended  for  maintenance  and  for  hori- 
zontal locomotion  and  comparing  the  remainder  with  the  meas- 
ured work  of  ascent.  The  results  given  in  the  previous  para- 
graph for  the  energy  expended  in  locomotion  were  computed 
according-  to  this  scheme. 

654.  Work  of  draft.  —  The  net  efficiency  in  draft  was  com- 
puted by  a  similar  method.     The  tread  power  was  set  nearly 
horizontal.     On  the  average  of  sixteen  trials  the  total  energy  out- 
put in  excess  of  maintenance  per  kilogram  live  weight  and  per 
meter  traveled  was  1.5021  cals.,  the  work  of  ascent  0.005115 
kilogram  meters  and  the  work  of  draft  0.153127  kilogram  meters. 
Letting  z  equal  the  energy  expended  in  the  performance  of  i 
kilogram  meter  of  work  of  draft,  the  following  equation  may 
be  formulated:  — 

x  +  0.005115  y  +  0.153127  z  =  1.5021  cals. 

Substituting  average  values  for  x  and  y,  the  value  of  z  is 
7.143  cals.,  equivalent  to  a  net  efficiency  of  32.84  per  cent. 

655.  Correction  for  speed.  —  In  experiments  made  at  a  walk 
it  was  found  that  the  expenditure  of  energy  per  meter  increased 
materially  as  the  speed  increased,  as  is  illustrated  by  the  aver- 
ages already  cited  (652)  and  is  shown  more  fully  in  a  succeed- 
ing paragraph  (663).     In  computing  the  efficiency  of  work  of 
ascent  or  draft,  it  is  necessary  to  take  account  of  this  fact. 
The  method  of  doing  so  is  a  method  of  approximation,  the  de- 
tails of  which  need  not  be  gone  into  here.1 

1  Compare  Armsby,  Principles  of  Animal  Nutrition,  pp.  507-508. 


WORK  PRODUCTION 


553 


656.  Summary.  —  The  following  table  contains  a  summary 
of  Zuntz  and  Hagemann's  results  regarding  the  efficiency  of 
the  body  of  the  horse  as  a  motor.  As  is  apparent  from  the 
foregoing  explanations,  the  table  shows  the  net  efficiency  in 
the  various  forms  of  work  into  which  the  total  work  done  can 
be  separated  in  the  manner  just  described  (651,  654). 

TABLE  155.  —  NET  EFFICIENCY  OF  THE  HORSE  IN  DIFFERENT  FORMS  OF 

WORK 


WORK  AT  A  WALK 

WORK  AT  A  SLOW  TROT 

Net  Expendi- 
ture of  Energy 

Net 
Effi- 
ciency 

Net  Expenditure 
of  Energy 

Net 
Effi- 
ciency 

cals. 

Kgm. 

% 

cals. 

Kgm. 

% 

For  i  kgm.  work  of  ascent,  without 

load  : 

6  8508 

2  9Il6 

34-3 

7.3647  l 

3.1300 

3I.Q61 

1  8  i  %  grade 

6  0787 

2  9660 

For  i  kgm.  work  of  ascent,  with  load: 

158%  grade 

36  2 

For  /  kgm.  work  of  draft: 

1.5%  grade      '     . 
8.5%  grade      

7-5I90 
10.3360 

3-I960 
4-3930 

31-3 
22.7 

7.4240     ! 
10.0780  2 

3-iSSo1 
4.28202 

3i-7j 
23-4* 

Locomotion  per  kg.  mass  per  meter 

without  load  : 

Speed  of  2.91  miles  per  hr.      ... 
Speed  of  3.36  miles  per  hr.      ... 
Speed  of  3.66  miles  per  hr.     .     .     . 
The  same  with  load  on  back  : 

0.3256 
0.3666 
0.3929 

O.S4781 

Speed  of  3.36  miles  per  hr.     .     .     . 

0.3914 

0.6O07  * 

657.  Relative  utilization  of  fats  and  carbohydrates.  —  In 
view  of  Chauveau's  theory4  that  fat  must  first  be  converted 
into  dextrose,  with  the  elimination  as  heat  of  a  considerable 
portion  of  its  energy,  before  it  can  serve  directly  as  a  source  of 
energy  for  the  physiological  processes,  it  becomes  of  much  in- 
terest to  inquire  to  what  relative  extent  the  energy  of  fats  and 
carbohydrates  is  utilized  in  muscular  work. 

In  Zuntz  and  Hagemann's  extensive  investigations,  particularly 
in  those  upon  the  horse,  there  were  very  considerable  variations 
in  the  proportions  of  fat  and  carbohydrates  katabolized.  The 
individual  trials  in  which  the  same  kind  of  work  was  per- 

1  Single  experiment.  2  Two  experiments.    Work  probably  excessive. 

3  Independent  of  speed. 

4  Compare  Armsby,  Principles  of  Animal  Nutrition,  pp.  153-154  and  399-405. 


554 


NUTRITION  OF  FARM   ANIMALS 


formed  also  show  in  many  cases  similar  variations.  Notwith- 
standing this,  however,  the  percentage  of  energy  utilized  did 
not  vary  materially  in  these  instances  and  there  is  no  indica- 
tion of  any  such  differences  as  would  be  expected  according  to 
Chauveau's  theory. 

The  question  has  also  been  investigated  directly  by  Zuntz 
and  his  associates  in  experiments  on  dogs  and  on  man.  In 
these  experiments,  the  feed  consisted  as  largely  as  possible  of 
the  nutrient  to  be  tested  (protein,  carbohydrates  or  fat,  respec- 
tively), so  that  the  body  metabolism  was  largely  at  its  expense. 
The  method  of  investigation  was  substantially  the  same  as 
that  which  has  just  been  described.  The  final  results  for  the 
energy  metabolism  per  kilogram  and  meter  traveled  were :  — 

TABLE  156.  —  COMPARISON  OF  NUTRIENTS  FOR  WORK  PRODUCTION 


RESPIRATORY 
QUOTIENT 

ENERGY  METAB- 
OLISM PER 
KILOGRAM   AND 
METER 

Proteins  only      

0.78 

Gram  calories 
2.58 

Chiefly  fat 

O  74. 

2  4.3 

Chiefly  fat  (body  freed  from  carbohydrates  by 
phloridzin)  

O.7I 

2.71 

Miuch  sugar  with  proteins 

O  71 

2  71 

Much  sugar  and  little  proteins       ... 

088 

2  6l 

The  differences  are  quite  small,  while,  as  Zuntz  points  out,  if 
2.6  cals.  represent  the  demand  for  energy  per  unit  of  work  when 
carbohydrates  are  the  source  it  should,  according  to  Chauveau's 
theory,  rise  to  about  3.68  cals.  when  the  energy  is  derived  ex- 
clusively from  fat. 

Later  and  more  elaborate  experiments  on  man  led  to  the  same 
conclusion.  Atwater  and  Benedict,1  Benedict  and  Milner,2 
and  Benedict  and  Cathcart3  also  report  experiments  upon 
men  which,  while  not  regarded  as  conclusive,  indicate  a  pos- 
sible slight  inferiority  of  fats  but  one  not  at  all  comparable  with 
that  demanded  by  Chauveau's  theory.  On  the  whole,  then, 

1  U.  S.  Dept.  of  Agric.,  Office  Expt.  Stas.,  Bui.  136  (1903),  182. 

2  U.  S.  Dept.  of  Agric.,  Office  Expt.  Stas.,  Bui.  175  (1907),  234. 

3  Muscular  Work ;   Carnegie  Institution  of  Washington,  Publ.  No.  187  (1913),  145. 


WORK  PRODUCTION  555 

the  conclusion  seems  warranted  that  if  any  difference  exists 
in  the  utilization  of  the  energy  of  fats  and  of  carbohydrates  it 
is  too  small  to  be  of  much  practical  significance. 

Conditions  affecting  efficiency 

658.  Efficiency   varies.  —  As   appears   from    the   foregoing 
summary  (656),  the  net  efficiency  of  the  animal  body  as  a 
motor  is  comparatively  high  in  the  case  of  the  horse,  considerably 
exceeding  in  most  instances  30  per  cent.     It  may  be  said  in  a 
broad  general  way  that  with  this  animal  about  one-third  of  the 
energy  metabolized  for  a  specific  form  of  muscular  exertion  (i.e., 
in  excess  of  maintenance  or  of  maintenance  plus  locomotion)  is 
recovered  in  the  mechanical  work  done.    It  is  also  evident, 
however,  that  the  organism  has  no  one  fixed  degree  of  efficiency 
but  that  the  latter  may  vary  through  a  somewhat  wide  range 
under  different  conditions. 

659.  Forms  of  work  done.  —  The  experiments  thus  far  cited 
refer  largely  to  work  done  by  walking  horizontally  or  up  a 
grade,  with  or  without  draft.     Of  all  the  forms  of  work  yet  in- 
vestigated, the  ascent  of  a  moderate  grade  or,  in  other  words, 
the  lifting  of  the  body  by  the  legs,  appears  to  be  the  one  which 
is  performed  most  economically,  a  net  efficiency  of  over  36 
per  cent  being  reported  both  for  the  horse  and  for  man.     This 
percentage,  however,  decreases  considerably  as  the  angle  of 
ascent  is  increased.     For  horizontal  locomotion,  as  already  noted 
(652),  Zuntz  computes  an  efficiency  of  35  per  cent.     Draft  up  a 
slight  grade  was  performed  somewhat  less  efficiently  in  the 
case  of   the    horse,    the  percentage  being  approximately  31, 
while  draft  up  an  8-J  per  cent  grade  was  done  with  an  efficiency 
of  less  than  23  per  cent. 

Other  forms  of  work  appear  to  be  performed  with  a  less 
degree  of  efficiency.  Thus  experiments  on  man  in  which  the 
work  was  done  by  turning  a  crank  with  the  hands  have  shown 
decidedly  lower  efficiencies  than  those  in  which  the  work  was 
done  on  a  treadmill.  The  same  was  true  in  the  experiments  of 
Benedict  and  Cathcart  on  man,  in  which  the  work  was  done  upon 
a  stationary  bicycle,  the  maximum  figures  computed  l  for  the 
net  efficiency  of  6  subjects  ranging  from  20.4  to  25.2  per  cent. 

1  Loc.  cit.,  p.  125. 


556  NUTRITION  OF  FARM  ANIMALS 

Species.  —  The  difference  just  noted  between  the  efficiency 
of  the  human  body  and  that  of  the  horse  is  evidently  due  largely 
to  differences  in  the  kind  of  work  performed,  since  the  work  of 
ascent  is  done  with  about  equal  efficiency  in  both  cases.  Klein  l 
finds  that  the  work  of  ascent  is  performed  by  the  ox  with  about 
the  same  net  efficiency  as  by  the  horse  but  that  the  former 
animal  expends  much  more  energy  in  horizontal  locomotion  per 
unit  of  distance  traveled  than  does  the  horse,  viz.,  about  0.53  to 
0.55  gram  calories,  per  meter  distance  and  kilogram  live  weight. 

660.  Individuality.  —  Zuntz   and   Hagemann's    experiments 
upon  the  horse  show  interesting  individual  differences  between 
animals,  presumably  due  to  differences  in  conformation.     For 
example,  Horse  No.  XIII  carried  a  given  load  on  his  back  with 
less  expenditure  of  energy  than  did  Horse  No.  III.     Horse  No. 
II  expended  more  energy  than  Horse  No.  Ill  in  horizontal 
locomotion  at  a  walk  but  less  in  trotting.     No.  II  likewise 
utilized  energy  to  a  slightly  less  extent  than  No.  Ill  in  ascend- 
ing a  grade  and  to  a  considerably  less  extent  in  horizontal  draft 
but,  on  the  other  hand,  like  No.  XIII,  carried  a  load  on  his 
back  more  economically  than  No.  III. 

The  possible  bearing  of  these  facts  upon  questions  of  heredity 
and  breeding  opens  up  an  interesting  field  of  speculation. 

661.  Training  and  fatigue.  —  It  is  a  familiar  experience  that 
any  unaccustomed  form  of  work  is  much  more  fatiguing  at  first 
than  it  is  later.     This  is  due  in  part  to  the  fact  that  in  making 
unfamiliar  motions  more  accessory  groups  of  muscles  are  called 
into  activity  than  are  necessary  later  when  more  skill  has  been 
acquired.     The  experience  of  a  learner  on  the  bicycle  is  an  ex- 
cellent example  of  this.     In  the  second  place,  however,  simple 
exercise  of  a  group  of  muscles  in  a  particular  way  seems  to  in- 
crease their  average  mechanical  efficiency. 

This  effect  may  be  illustrated  by  the  results  of  two  series 
of  experiments  by  Gruber  upon  himself  in  which  he  de- 
termined the  carbon  dioxid  excreted  during  work.  Thus  in 
hill  climbing  the  amounts  excreted  in  twenty  minutes  were :  — 

Series  I : 

Hill  climbing  without  practice 40.98  grams 

Hill  climbing  after  12  days'  practice    ....     32.22  grams 

^entbl.  Physiol.,  26  (1912),  722. 


WORK  PRODUCTION  557 

Series  II : 

Hill  climbing  without  practice 38.83  grams 

Hill  climbing  after  14  days'  practice    .     .     .     .     31.00  grams 

That  the  less  use  of  accessory  muscles  is  not  the  only  cause 
of  this  increase  in  efficiency  is  indicated  by  experiments  upon 
convalescents,  which  have  shown  that  the  gradual  strengthening 
of  the  muscles  results  in  a  more  economical  performance  of 
their  work,  largely  independent  of  any  special  training  for  a 
particular  kind  of  work. 

Conversely,  fatigue  has  been  shown  by  numerous  observers 
to  materially  increase  the  relative  amount  of  metabolism  per 
unit  of  work.  Schnyder  l  summarizes  the  matter  in  the  state- 
ment that  it  is  not  the  work  itself  but  the  muscular  effort  re- 
quired which  determines  the  amount  of  metabolism,  a  conclu- 
sion which  seems  to  have  anticipated  Hill's  results  2  regarding 
the  relation  of  muscular  tension  to  metabolism. 

662.  Intensity  of  Work.  —  It  has  already  been  shown  (649) 
that  the  gross  efficiency  of  the  body  tends  to  increase  with  the 
intensity  of  work,  i.e.,  with  the  number  of  units  of  work  per- 
formed in  a  unit  of  time,  for  the  reason  that  the  proportion 
of  the  total  energy  expended  which  is  devoted  to  useful  work 
increases.     On  the  other  hand,  common  observation  tends  to 
show  that  this  can  be  true  only  within  limits,  and  that  excessive 
work  is  performed  uneconomically. 

The  intensity  of  the  work  may  be  increased  by  increasing 
either  the  speed,  the  load  moved,  or  the  angle  of  ascent.  It 
would  be  anticipated,  therefore,  that  an  undue  increase  of  any 
one  of  these  factors  would  result  in  a  diminished  net  efficiency. 

663.  Influence  of  speed.  —  That  great  speed  in  horizontal 
locomotion  involves  a  largely  increased  expenditure  of  energy  is 
evident.     The  race  horse  or  the  track  athlete  traveling  a  mile 
at  top  speed  obviously  metabolizes  vastly  more  energy  than 
one  traveling  the  same  distance  at  a  moderate  rate. 

In  the  case  of  the  horse,  Zuntz  and  Hagemann's  results  on 
horizontal  locomotion  at  a  walk  (652)  show  an  increased  net 
expenditure  of  energy  per  kilogram  weight  and  meter  distance 
with  increased  speed,  while  locomotion  at  a  trot  showed  no 
distinct  increase  up  to  a  speed  of  about  7^  miles  an  hour. 

1  Ztschr.  Biol.,  33  (1896),  289.  2  Jour.  Physiol.  (London),  42  (19"),  i. 


558  NUTRITION  OF  FARM  ANIMALS 

Much  study  has  been  expended  upon  horizontal  locomotion  in 
man.  The  somewhat  extensive  literature  of  the  subject  as  sum- 
marized by  Benedict  and  Murschhauser l  shows  clearly  a  marked  in- 
crease in  the  net  expenditure  of  energy  per  unit  of  locomotion  as  the 
speed  increases.  Brezina  and  Reichel 2  found  that  beyond  a  certain 
maximum  speed  (about  80  meters  per  minute)  it  became  an  exponen- 
tial function  of  the  velocity,  while  below  that  speed  only  slight  varia- 
tions were  shown. 

The  influence  of  speed  upon  the  net  efficiency  in  work  of  ascent 
seems  to  be  much  less  marked  than  that  upon  the  expenditure  in 
locomotion.  No  results  upon  the  horse  are  available.  With  man, 
Brezina,  Kolmer  and  Reichel 3  in  experiments  on  a  tread  power  found 
that  the  net  expenditure  per  kilogram  and  meter  distance  in  walking 
up  a  grade  was  substantially  independent  of  speed  at  velocities  con- 
siderably below  the  maximum  just  indicated.  Since  this  was  found 
to  be  true  also  of  horizontal  locomotion,  it  follows  that  the  efficiency 
in  work  of  ascent  must  also  have  been  nearly  independent  of  the  speed. 

Benedict  and  Cathcart 1  found  that  both  the  net  and  gross  efficiency 
in  work  done  on  their  bicycle  ergometer,  which  might  be  regarded  as 
a  form  of  draft,  decreased  as  the  speed  increased.  In  none  of  the 
various  experiments  cited  was  there  any  air  resistance,  the  work  being 
done  on  a  stationary  apparatus.  In  actual  practice  this  is  an  im- 
portant factor  at  high  speeds,  increasing  very  much  more  rapidly 
than  the  speed. 

664.  Influence  of  gait.  —  According  to  Zuntz  and  Hage- 
mann's  results  (656)  an  increase  of  speed  in  the  horse  obtained 
by  a  change  of  gait  from  a  walk  to  a  trot  involves  a  notable 
increase  in  the  net  energy  expended  for  locomotion  per  unit  of 
weight  and  distance,  although  an  increase  in  the  trotting  speed 
up  to  a  moderate  limit  causes  no  further  increase.  With  man, 
on  the  contrary,  Benedict  and  Murschhauser  find  that  locomo- 
tion at  a  given  speed  is  performed  more  economically  in  running 
than  in  walking. 

Such  differences  are  doubtless  brought  about  to  a  consider- 
able extent  by  differences  in  the  height  to  which  the  body 
is  lifted  at  each  step  and  the  degree  to  twhich  extraneous 
motions,  such  as  swinging  the  arms  in  rapid  walking,  are 
brought  into  play. 

1  Carnegie  Institution  of  Washington,  Publication  No.  231  (1915),  pp.  12-28. 

2  Biochem.  Ztschr.,  63  (1914),  170. 

3  Biochem.  Ztschr.,  65  (1914),  16  and  35. 

4  Carnegie  Institution  of  Washington,  Publication  No.  187  (1913),  138. 


WORK  PRODUCTION 


559 


665.  Influence  of  load.  —  With  the  horse,  Zuntz  and  Hage- 
mann  find  that  carrying  a  load  on  the  back  causes  a  distinct 
increase  in  the  net  expenditure  for  horizontal  locomotion  per 
unit  of  mass  moved.     The  work  of  ascent,  on  the  contrary, 
was  performed  with  at  least  as  high  an  efficiency  by  an  animal 
carrying  a  weight  as  by  one  without  load.     With  man,  Bene- 
dict and  Cathcart  find  the  net  efficiency  but  little  affected  by  the 
amount  of  resistance  in  their  bicycle  ergometer.     Brezina  and 
Reichel  find  that  at  moderate  speeds  the  load  carried  by  a  man 
affects  but  slightly  the  net  expenditure  per  kilogram  and  meter 
distance  but  that  above  the  point  at  which  the  speed  begins 
to  affect  the  latter,  the  increase  is  greater  as  the  load  is  increased. 

666.  Influence  of  grade.  —  The  net  efficiency  with  which 
work  of  ascent  is  done  decreases  as  the  grade  is  made  steeper. 
Zuntz  and  Hagemann  in  their  experiments  upon  the  horse  ob- 
served a  decrease  of  the  efficiency  from  34.3  per  cent  to  33.7  per 
cent  as  the  grade  was  increased  from  10.7  per  cent  to  18.1  per 
cent,  while  for  work  of  draft  the  efficiency  was  31.3  per  cent  on  a 
0.5  per  cent  grade  but  only  22.7  per  cent  on  an  8.5  per  cent  grade. 

That  the  same  is  true  in  the  case  of  man  is  illustrated  in  experi- 
ments by  Loewy,  who  obtained  the  following  results  on  three 
different  individuals. 

TABLE  157.  —  INFLUENCE  OF  GRADE  ON  NET  EFFICIENCY  IN  WORK 
PRODUCTION 


GRADE  PER  CENT 

NET  EFFICIENCY 

A.  L. 

J.L. 

L.  Z. 

23 
30.5 
36.6 

34-3 
34-3 
29.0 

36.1 
32.6 

32.3 

36.6 
36.6 
32.2 

The  same  conclusion  was  reached  in  the  recent  investigations 
of  Brezina  and  his  associates  1  on  man.  From  an  extensive 
series  of  experiments  they  compute  the  net  efficiency  to  have 
been  approximately :  — 

1  Biochem.  Ztschr.,  63  (1914),  170;  65  (1914),  16. 


560  NUTRITION  OF  FARM  ANIMALS 

GRADE  NET  EFFICIENCY 

10%  39% 

20%  3I% 

30%  27% 

§  3.   FEED  REQUIREMENTS  FOR  WORK 

As  is  the  case  in  feeding  for  other  purposes,  the  working  animal 
needs  to  be  supplied  with  an  adequate  amount  of  energy  in 
available  form  and  with  certain  specific  forms  of  matter,  par- 
ticularly proteins  and  ash  ingredients. 

The  requirements  of  matter 

667.  Functions  of  protein.  —  As  shown  in  Chapter  IX  (418), 
the  daily  protein  requirement  of  the  horse  for  simple  mainte- 
nance is  apparently  about  the  same  as  that  of  other  farm  ani- 
mals, viz.,  approximately,  0.6  pound  of  digestible  crude  protein 
per  1000  pounds  live  weight,  although  the  experimental  data 
are  rather  scanty. 

It  appeared  in  §  i  of  this  chapter  (641-643)  that  the  energy  ex- 
pended in  muscular  work  is  practically  derived  from  the  katab- 
olism  of  carbohydrates  and  fats,  the  protein  katabolism  being 
unaffected  by  work  so  long  as'an  ample  supply  of  non-nitrog- 
enous nutrients  is  available.  One  might  at  first  thought  be 
inclined  to  conclude,  therefore,  that  the  simple  addition  of  non- 
nitrogenous  material  to  a  maintenance  ration  would  suffice  to 
enable  it  to  support  a  corresponding  amount  of  work  production 
and  that  a  maintenance  ration  of  digestible  protein  would  also 
be  a  sufficient  supply  for  the  working  horse.  Such  a  conclu- 
sion would,  however,  be  premature.  It  is  quite  conceivable 
that  in  order  to  maintain  the  muscle  as  an  efficient  instrument 
for  converting  chemical  energy  into  mechanical  work,  a  higher 
plane  of  protein  metabolism  may  be  necessary  than  is  required 
to  support  it  in  nitrogen  equilibrium  when  doing  no  work, 
while  the  possibility,  for  example,  of  a  favorable  influence  of 
an  abundant  protein  supply  on  the  blood  circulation  and  on 
the  nervous  system  should  not  be  overlooked.  In  fast  work 
especially,  the  demand  of  the  animal  for  oxygen  reaches  a 
high  level.  Since  the  blood  is  the  vehicle  by  which  oxygen  is 
introduced  into  the  body,  an  adequate  stock  of  blood,  or 


WORK  PRODUCTION  561 

more  particularly  of  haemoglobin,  would  be  necessary  and  a 
liberal  supply  of  protein  seems  to  assist  in  securing  this.  If 
any  of  these  conjectures  should  prove  to  be  true  the  proteins 
may  play  a  not  insignificant  role  in  the  production  of  muscular 
work  without  any  evidence  of  the  fact  appearing  in  the  total 
nitrogen  excretion. 

668.  The  protein  requirement.  —  No  specific  investigations 
regarding  the  minimum  protein  requirement  of  the  work  horse 
seem  to  have  been  made,  but  the  extensive  experiments  of 
Wolff,  Grandeau,  Miintz  and  others  referred  to  on  previous 
pages  afford  numerous  instances  in  which  entirely  satisfactory 
results  were  obtained  from  rations  comparatively  low  in  pro- 
tein, although  in  none  of  them  was  the  supply  reduced  to  the 
maintenance  requirement.  Similarly,  in  Langworthy's  ex- 
tensive compilation  1  of  rations  fed  in  practice,  numerous  ex- 
amples of  low  protein  rations  are  to  be  found. 

In  fact,  it  would  be  difficult  to  compound  from  ordinary  feed- 
stuffs  a  ration  sufficient  to  support  any  considerable  amount  of 
work  without  introducing  more  protein  than  is  presumably 
required  for  simple  maintenance.  Such  being  the  case,  the 
principal  point  to  be  taken  into  consideration  is  the  effect  of  a 
reduced  protein  supply  upon  the  digestibility  of  the  ration  (723- 
725).  Any  ration  carrying  sufficient  protein  to  ensure  normal 
digestion  would  doubtless  furnish  ample  protein  for  work 
production  in  all  ordinary  cases,  with  the  possible  exception  of 
work  at  high  speed.  A  nutritive  ratio,  computed  in  the  usual 
way  (709),  of  i :  10  or  i :  12  would  unquestionably  ensure  ample 
protein  for  slow  work,  and  probably  for  moderately  rapid  work 
also.  In  the  case  of  man,  as  is  well  known,  experience  or  tra- 
dition have  led  to  the  general  employment  of  high  protein 
rations  by  athletes.  On  the  other  hand,  however,  Chittenden  2 
has  shown  that  the  protein  supply  of  athletes  and  soldiers,  as 
well  as  that  of  men  of  sedentary  occupations,  may  be  reduced 
much  below  the  usual  level  without  loss  of  efficiency.  Even  in 
these  experiments,  however,  the  protein  supply  was  much  higher 
than  the  amounts  which  recent  experiments  have  shown  to  suf- 
fice for  the  maintenance  of  nitrogen  equilibrium  in  man  at  rest 
or  doing  only  light  work. 

1  U.  S.  Dept.  Agri.,  Office  Expt.  Sta.,  Bui.  125  (1903). 

2  Physiological  Economy  in  Nutrition,  1904. 
2  O 


562  NUTRITION  OF  FARM   ANIMALS 

669.  Ash  requirements.  —  As  pointed  out  in  previous  chap- 
ters, the  ash  requirements  of  an  animal  deserve  greater  con- 
sideration than  they  generally  receive,  while  in  the  case  of 
growth,  at  least,  the  presence  of  certain  accessory  substances 
in  the  ration  is  necessary.  So  far  as  the  working  horse  is  con- 
cerned, however,  no  sufficient  data  seem  available  for  a  dis- 
cussion of  these  topics. 


The  energy  requirement 

670.  Economic,  or  over-all  efficiency.  —  In  the  preceding 
section  certain  comparisons  were  made  between  the  efficiency  of 
the  animal  body  as  a  prime  motor  and  that  of  artificial  engines. 
The  animal  body,  however,  is  not  only  a  prime  motor  but  in- 
cludes also  the  furnace  in  which  the  fuel  is  burned  and  resembles 
in  this  respect  a  complete  power  plant,  such  as  a  locomotive, 
for  example,  rather  than  an  engine. 

Just  as  the  energy  of  the  fuel  of  a  locomotive  is  subject  to 
certain  losses  due  to  incomplete  combustion  and  to  radiation  of 
heat  before  the  steam  reaches  the  cylinders,  so  portions  of  the 
energy  of  the  feed  escape  in  the  excreta  or  are  expended  in  the 
various  processes  incident  to  the  formation  in  the  body  of  those 
substances  whose  katabolism  yields  the  energy  for  a  muscular 
contraction. 

Since  these  losses  and  expenditures  are  largely  unavoidable, 
they  constitute  part  of  the  energy  requirements  of  the  work 
animal,  and  from  the  economic  point  of  view  the  efficiency  of 
the  animal  is  measured  by  a  comparison  of  the  total  feed  energy 
with  the  work  done.  This  might  be  called  the  economic  effi- 
ciency, comparable  to  the  over-all  efficiency  of  a  steam  plant  as 
computed  by  a  comparison  of  coal  consumption  with  the  brake 
horse  power  obtained.  Any  such  comparisons,  of  course, 
must  take  account  of  the  maintenance  requirement  of  the 
animal  when  doing  no  work  and  must  therefore  be  made  on  the 
basis  of  the  24-hour  output  of  work  (650). 

Few  satisfactory  direct  determinations  of  the  economic  effi- 
ciency of  work  animals  in  the  foregoing  sense,  i.e.,  of  the  re- 
lation of  the  work  done  to  the  feed  (or  total  feed  energy)  required 
for  its  performance,  have  yet  been  reported. 


WORK  PRODUCTION  563 

The  extensive  investigations  on  the  work  horse  initiated  at  Hohen- 
heim  by  Kellner  and  continued  under  Wolff's  direction,  and  which 
have  been  referred  to  in  Chapter  VIII  (386  a)  in  their  bearing  upon 
the  maintenance  requirement,  were  intended  primarily  to  determine 
the  energy  requirements  for  work.  Unfortunately,  however,  as  there 
noted,  the  measurements  of  the  work  done  in  the  earlier  experiments 
were  subsequently  discovered  to  be  inaccurate.  In  the  comparatively 
few  later  experiments  of  1891-94,  various  mixed  rations  were  fed. 
While,  therefore,  the  total  energy  consumed  per  unit  of  work  could 
be  computed,  only  few  and  uncertain  data  for  individual  feeding 
stuffs  can  be  deduced  and  the  results  are  therefore  of  small  general 
value  for  the  particular  phase  of  the  subject  under  discussion  here. 

671.  Net  energy  values  for  work  production.  —  The  ques- 
tion of  the  energy  requirement  of  the  work  animal  may,  how- 
ever, be  approached  in  a  somewhat  different  way. 

The  energy  expended  in  work  production,  as  already  stated 
(630,  631) ,  is  derived  primarily  from  the  katabolism  of  body  sub- 
stances. The  function  of  the  feed  so  far  as  energy  is  concerned 
is  to  replace  in  the  body  the  energy  thus  expended.  The  net 
energy  value  of  a  feeding  stuff  for  work  production,  then,  is 
measured  by  the  amount  of  body  energy  which  it  can  thus  re- 
place. The  case  is  precisely  parallel  to  that  of  maintenance  as 
discussed  in  Chapter  VIII  (370).  The  net  energy  value  of  a 
feeding  stuff  for  the  latter  purpose  is  measured  by  the  extent  to 
which  it  prevents  loss  of  body  energy  as  a  consequence  of  in- 
ternal work,  while  the  net  energy  value  for  the  former  purpose 
is  measured  by  the  extent  to  which  it  prevents  or  makes  good 
a  loss  of  body  energy  due  to  external  work.  Conversely,  the 
working  animal  requires  in  addition  to  maintenance  a  supply 
of  net  energy  in  its  ration  equal  to  the  amount  of  body  energy 
katabolized  for  work  production. 

In  view  of  this  close  similarity  between  the  functions  of  feed 
in  maintenance  and  in  work  production,  the  assumption  seems 
warranted  that  the  net  energy  values  of  feeding  stuffs  for  these 
two  purposes  are  substantially  the  same.  Thus  in  an  exper- 
iment with  a  steer  already  described  (364),  it  was  found  that  one 
pound  of  timothy  hay  contributed  502  Cals.  to  the  maintenance 
of  the  animal.  If  the  same  animal  had  been  required  to  do  167 
Cals.  of  external  work  and  had  performed  it  with  the  same  aver- 
age net  efficiency  as  the  horse,  viz. ,  about  one- third,  he  would  have 


564  NUTRITION  OF  FARM   ANIMALS 

katabolized  body  substance  containing  167  -5-  J  =  502  Cals. 
of  energy  and  it  would  be  anticipated  that  one  pound  of  timothy 
hay  would  have  been  sufficient  to  replace  this  energy  in  the  body. 
Similarly,  the  performance  of  1000  Cals.  of  external  work  by  a 
horse  would  cause  the  mobilization  of  about  3000  Cals.  of  body 
energy,  and  the  feed  necessary  to  support  this  work  would  have 
to  supply  about  3000  Cals.  of  net  available  energy. 

In  brief,  the  net  energy  values  for  maintenance,  determined 
in  the  manner  described  in  Chapter  XVII  and  tabulated  in  the 
Appendix,  may  be  regarded  as  also  net  energy  values  for  work 
production,  and  the  energy  requirements  of  the  work  animal 
may  be  expressed  in  terms  of  these  net  energy  values. 

672.  Net  energy  requirements.  —  It  is  plain,  in  the  light  of 
the  foregoing  discussion,  that  the  amount  of  net  energy  required 
by  an  animal  for  work  production  may  be  regarded  as  equal  to 
the  body  energy  metabolized  in  the  performance  of  the  work. 

From  the  data  contained  in  §  2,  it  is  possible  to  estimate  ap- 
proximately how  much  energy  in  excess  of  its  maintenance  re- 
quirement must  be  mobilized  in  the  body  of  a  horse,  e.g.,  to 
perform  a  known  amount  of  mechanical  work  of  a  specific  kind. 
Thus  a  horse  in  hauling  a  load  having  a  draft  of  100  pounds 
20  miles  on  a  level  road  would  do  10,560  foot  tons  of  mechanical 
work,  equivalent  to  3421  Calories.  Table  155  (651)  shows 
the  net  efficiency  of  the  horse  in  draft  to  be  about  31.3  per  cent. 
Accordingly,  the  animal  would  have  to  mobilize  in  his  body  for 
the  performance  of  this  work  4321  -f-  0.313  =  10,929  Calories, 
and  his  feed  must  therefore  supply  this  amount  of  net  energy 
in  addition  to  the  requirements  for  locomotion,  maintenance  or 
other  purposes. 

The  total  expenditure  of  body  energy  during  the  performance 
of  work  by  the  horse,  as  appears  from  §  2,  includes  substantially 
four  factors  in  varying  proportions,  viz.,  the  expenditure  for 
maintenance,  for  horizontal  locomotion,  for  ascent  (or  descent) 
and  for  draft.  A  fairly  accurate  estimate  of  the  net  energy 
required  to  do  a  certain  piece  of  work  may  therefore  be  obtained 
by  computing  the  requirement  for  each  of  these  factors  sepa- 
rately from  the  data  for  net  efficiency  already  recorded  and 
adding  the  results. 

For  example,  let  it  be  supposed  that  a  horse  weighing  noo 
pounds  hauls  a  load  of  2000  pounds,  having  a  horizontal  draft 


WORK  PRODUCTION  565 

of  100  pounds,  15  miles  per  day,  including  5  miles  up  a  i  per 
cent  grade,  at  a  speed  of  3!  miles  per  hour.  The  mechanical 
work  performed  consists  of  lifting  the  weight  of  the  animal  plus 
the  load  264  feet  and  in  overcoming  a  draft  resistance  of  100 
pounds  through  79,200  feet.  The  total  mechanical  work,  there- 
fore is  as  follows :  — 

TABLE  158.  —  EXAMPLE  OF  COMPUTATION  OF  WORK  DONE 

Draft  100  X  5280  X  15  =  7,920,000  foot  pounds  =  2.565  Therms 

Ascent  3100  X  264  =     818,400  foot  pounds  =  0.265  Therms 

Total  8,738,400  foot  pounds  =  2.830  Therms 

The  amount  of  body  energy  which  the  horse  must  metabolize 
in  the  performance  of  this  daily  task  will  be  that  corresponding 
to  the  mechanical  work  of  draft  and  of  ascent,  computed  from 
the  percentages  in  Table  155,  together  with  the  energy  ex- 
pended in  locomotion  according  to  the  same  table  and  the  energy 
requirement  for  maintenance.  The  total  requirement  of  net  en- 
ergy per  day,  therefore,  will  be  as  follows : l  — 

TABLE  159.  —  EXAMPLE  OF  COMPUTATION  OF  NET  ENERGY  REQUIREMENT 

For  draft               2.565  -f-    0.313  =    8.195  Therms 

For  ascent             0.265  -*-    0.343  =    0.773  Therms 

For  locomotion     0.262X15  =    3.930  Therms 

For  maintenance  (385)  4-356  Therms 

Total  1 7. 254  Therms 

673.  Calculation  of  rations.  —  Having  in  some  such  way  as 
that  just  illustrated  determined  the  net  energy  requirement  of 
the  work  horse  it  is  evident  that  the  corresponding  ration  may 
be  computed  if  the  net  energy  values  of  the  feeding  stuffs  to  be 
used  are  known.  Unfortunately,  in  the  case  of  the  horse,  the 
principal  work  animal  of  the  United  States,  such  net  energy  values 
of  feed  stuffs  as  we  now  possess  have  not  been  directly  deter- 
mined but  are  the  results  of  somewhat  complicated  calcu- 
lations (775-778) .  For  the  ox,  on  the  contrary,  fairly  satisfactory 
data  regarding  the  net  energy  values  of  feed  stuffs  are  available 
(760,  773,  774),  but  in  this  case  very  few  determinations  of  the 
efficiency  of  the  animal's  body  in  work  production  have  yet  been 

1  The  computation  could  be  somewhat  simplified  by  assuming  a  uniform  net 
efficiency  of  5  for  all  forms  of  work. 


566  NUTRITION  OF  FARM  ANIMALS 

reported,  although  the  indications  are  (659)  that  it  is  not  widely 
different  from  that  of  the  horse. 

Using  the  net  energy  values  for  the  horse  obtained  by  Zuntz  and 
Hagemann's  method  of  computation  and  contained  in  Table  VIII 
of  the  Appendix,  rations  may  readily  be  computed  for  this  animal 
in  the  same  general  manner  as  for  any  other,  their  accuracy  de- 
pending upon  the  accuracy  of  the  net  energy  values  used.  Thus, 
in  the  case  just  supposed,  the  requirement  of  net  energy  was 
17.254  Therms.  From  the  figures  of  the  table  it  is  easy  to  com- 
pute that  the  following  ration  would  meet  the  requirement. 

TABLE  160.  —  EXAMPLE  OF  RATION  FOR  WORK 

NET  ENERGY 

10  Ib.  meadow  hay 3. 270  Therms 

10  Ib.  oats 8.820  Therms 

4.1  Ib.  maize 5.164  Therms 

17.254  Therms 

The  principal  difficulty  in  practice  lies  in  the  determination 
of  the  amount  of  work  done.  With  farm  animals  doing  a  va- 
riety of  work  at  more  or  less  irregular  intervals,  it  seems  hardly 
possible  to  make  any  computation  of  the  mechanical  work 
performed  which  would  be  trustworthy  or  which  would  justify 
the  time  consumed.  The  sufficiency  of  the  ration  of  the  farm 
horse  will  ordinarily  be  judged  of  by  the  live  weight  and  con- 
dition of  the  animal,  and  the  principal  use  of  tables  of  net  energy 
values  will  be  as  an  aid  in  securing  the  necessary  feed  energy 
at  the  cheapest  rate  per  unit. 

On  the  other  hand,  where  a  large  number  of  horses  or  mules 
are  used  for  the  same  kind  of  work  under  uniform  conditions  it 
would  seem  possible  to  make  fairly  reliable  estimates  of  the 
work  done  and  to  compute  feed  requirements  with  a  reasonable 
degree  of  accuracy.  It  appears  not  unlikely  that  such  compu- 
tations might  lead  to  considerable  economy,  since,  as  was  pointed 
out  in  considering  the  maintenance  requirements  of  the  horse 
(392),  a  surplus  of  feed  seems  especially  apt  to  stimulate  this 
animal  to  restlessness  and  an  unnecessary  expenditure  of  en- 
ergy in  minor  muscular  activities. 

674.  Feeding  standards  for  the  horse.  —  More  or  less  ar- 
bitrary estimates  for  light,  medium,  and  heavy  work  may  also 
be  formulated,  as  has  been  done  by  various  writers. 


WORK  PRODUCTION 


567 


According  to  Wiist 1  a  horse  weighing  1000  pounds  is  capable 
of  performing  daily  about  two  million  kilogram  meters  of  work, 
inclusive  of  that  of  locomotion.  Allowing  for  the  work  of 
locomotion,  this  seems  to  agree  well  with  Thurston's  statement : 2 
"  It  is  customarily  assumed  that  a  horse  may  develop  22,500 
foot-pounds  per  minute  throughout  a  day's  work  of  eight  hours." 
If  this  may  be  regarded  as  full  work  and  if  the  average  net 
efficiency  of  the  animal  be  taken  as  one- third,  the  net  energy 
requirements  for  the  work  itself  and  the  total  requirements, 
inclusive  of  maintenance,  would  be  as  follows :  — 


TABLE  161.  —  NET  ENERGY  REQUIREMENTS  OF  THE  HORSE 


WORK  PER- 
FORMED 

NET  ENERGY 
REQUIRED  FOR 
WORK 

TOTAL  ENERGY 
REQUIREMENTS 

Full  work    
Half  work  
One-fourth  work       .     .     . 

4.688  Therms 
2.344  Therms 
1.172  Therms 

14.06  Therms 
7.03  Therms 
3.52  Therms 

18.16  Therms 
11.13  Therms 
7.62  Therms 

It  should  be  noted  that  the  discussions  of  the  foregoing  pages 
apply  specifically  to  the  work  horse  and  the  results  have  only 
a  limited  application  to  the  feeding  of  pleasure  or  race  horses. 
With  such  animals,  the  cost  of  feed  is  economically  a  very 
minor  factor  and  success  depends  on  experience  and  skill 
rather  than  on  mathematical  computations.  That  a  fairly 
liberal  supply  of  protein  in  rations  for  fast  work  is  indicated 
by  physiological  considerations  has  been  already  pointed  out 
(667). 

675.  Comparison  with  power  plant.  —  As  stated  (670),  no 
satisfactory  direct  determinations  of  the  over-all  efficiency  of 
work  animals  are  recorded,  but  it  may  be  computed  in  a  case 
like  that  used  as  an  illustration  on  a  previous  page  (672,  673). 
There  the  total  useful  work  was  2.830  Therms,  while  the  gross 
energy  of  the  computed  ration  would  be  approximately  55.800 
Therms  and  the  over-all  efficiency,  therefore,  2.830  -r-  55.800  = 
5.1  per  cent.  As  was  shown  in  §  2  (649)  to  be  the  case  with  the 

1  Cited  by  Kellner,  Die  Ernahrung  der  landw.  Nutztiere,  6th  Ed.,  p.  465. 

2  The  Animal  as  a  Machine  and  a  Prime  Motor,  1894. 


568  NUTRITION  OF   FARM  ANIMALS 

gross  efficiency  of  the  body,  however,  this  percentage  will  vary 
from  case  to  case.  It  will  increase  with  the  intensity  of  the 
work  and  decrease  with  the  number  of  hours  the  animal  is  idle 
per  day,  i.e.,  it  will  vary  as  the  ratio  of  useful  work  to  main- 
tenance requirement  varies.  In  the  case  supposed,  the  animal 
worked  6  hours  per  day.  If  we  imagine  his  bodily  machinery 
stopped  for  the  remaining  18  hours,  as  an  engine  might  be,  and 
charge  him  with  only  J  of  his  24-hour  maintenance  require- 
ment, the  total  feed  energy  necessary  would  be  reduced  to  about 
45.230  Therms  and  the  over-all  efficiency  during  the  hours  of 
work,  computed  on  this  basis,  would  be  6.26  per  cent,  or  about 
that  of  a  modern  steam  locomotive.  In  actual  practice,  the  con- 
ditions with  an  animal  are  very  much  as  if  it  were  necessary  to 
keep  up  a  full  head  of  steam  for  24  hours  or  as  if  an  internal  com- 
bustion motor  were  to  be  run  continuously  although  actual 
work  was  being  done  for  only  a  portion  of  the  time. 


PART    IV 
THE    FEED   SUPPLY 


CHAPTER  XV 

THE   FEEDING  STUFFS 

676.  Sources  of  feeding  stuffs.  —  In  the  several  chapters  of 
Part  III  the  feed  requirements  of  different  classes  of  farm 
animals  and  for  different  forms  of  production  have  been  con- 
sidered. 

In  the  more  primitive  forms  of  animal  husbandry,  such  as 
the  pastoral  husbandry  of  ancient  times  or  the  range  feeding 
of  the  western  United  States,  these  requirements  were  met  by 
the  consumption  of  the  natural  products  of  the  soil.  Increas- 
ing population  and  rising  land  values,  however,  mevitably 
tend  to  the  displacement  of  pastoral  agriculture  by  more  in- 
tensive forms  in  which  a  much  greater  variety  of  feeding  stuffs 
is  available  for  domestic  animals.  Forage  crops  are  grown 
for  use  in  the  winter  and  to  supplement  the  deficiencies  of  the 
pasture ;  grain  is  produced  in  excess  of  the  effective  demand  for 
human  consumption  and  utilized  as  stock  feed ;  finally,  as  this 
surplus  of  grain  decreases  with  the  growing  requirement  for 
human  food,  a  great  variety  of  residues  from  the  preparation 
of  the  crude  products  of  the  farm  for  man's  use,  the  by-product 
feeds,  becomes  available  to  the  stockman. 

It  does  not  fall  within  the  province  of  the  present  work  to 
consider  either  the  problems  of  agronomy  connected  with  the 
production  of  feeding  stuffs  or  the  technical  details  of  the 
manufacturing  processes  which  yield  the  various  by-product 
feeds,  but  a  brief  consideration  of  the  general  properties  of  the 
principal  classes  of  feeding  stuffs  seems  desirable  as  an  intro- 
duction to  the  discussion  of  the  principles  determining  their 
nutritive  values 

677.  Classification.  —  The  three  main  classes  of  feeding  stuffs, 
as  already  stated  in  Chapter  II  (111),  are  the  coarse  fodders, 
or  roughages,  consisting  of  the  vegetative  organs  of  plants,  the 
roots  and  tubers,  and  the  concentrates,  the  latter  comprising 
both  the  grains  and  similar  farm  products  and  the  by-products 
of  divers  industries.     The  members  of  these  three  classes  of 


572  NUTRITION  OF  FARM  ANIMALS 

feeding  stuffs  may  be  variously  grouped  for  different  purposes, 
but  the  following  scheme,  although  not  strictly  consistent, 
may  serve  the  purpose  of  this  discussion. 

Classification  of  feeding  stuffs 

Roughages,  or  coarse  fodders. 
Dried 

Grasses 

Legumes 

Straws 
Fresh 

Grasses 

Legumes 
Silage 

Roots  and  tubers 
Concentrates 

Farm  products 

Cereal  grains 

Leguminous  grains 

Oil  seeds 

Dairy  products 
By-products 

By-products  of  milling 

By-products  of  fermentation  industries 

By-products  of  oil  extraction 

By-products  of  starch  and  glucose  manufacture 

By-products  of  sugar  manufacture 

By-products  of  the  packing  house 

The  following  characterization  of  these  various  classes  of 
feeding  stuffs  is  reproduced  without  material  change  from  an 
earlier  article  by  the  writer.1 


§  i.   ROUGHAGES,  OR  COARSE  FODDERS 

678.  General  characters.  —  The  roughages  are  charac- 
terized chemically  by  a  relatively  large  percentage  of  crude 
fiber,  which  forms  the  framework  of  the  plant.  They  usually 
do  not  contain  very  much  protein,  although  in  some  this  ingre- 
dient shows  a  fairly  high  percentage.  The  proportion  of  crude 

1  Bailey's  Cyclopedia  of  American  Agriculture,  1908,  Vol.  Ill,  pp.  58-92. 


THE  FEEDING  STUFFS 


573 


fat  is  small  and  includes  much  besides  true  fat.  The  nitrogen- 
free  extract,  along  with  more  or  less  starch  and  sugar,  includes  a 
great  variety  of  less  familiar  carbohydrates  and  of  other  sub- 
stances whose  nutritive  value  is  problematical.  By  far  the 
larger  proportion  of  the  roughages  in  common  use  is  supplied 
by  two  classes  of  plants,  —  the  grasses  (Gramineae),  including 
maize,  and  the  legumes  (Leguminosae).  Furthermore,  crops 
belonging  to  both  these  classes  may  be  used  for  fodder  when 
but  partially  mature  (hay,  maize  forage),  or  they  may  be  al- 
lowed to  ripen,  the  grain  may  be  removed,  and  the  residue 
(straw,  stover)  used  for  feeding. 

679.  The  grasses.  —  The  larger  share  of  the  hay  crop  and 
of  the  pasturage  of  the  United  States  is  supplied  by  plants  known 
in  a  restricted  and  popular  sense  as  grasses,  such  as  timothy, 
blue-grass,  red- top.  To  these  must  be  added,  as  a  most  impor- 
tant source  of  forage  in  the  United  States,  maize,  or  Indian 
corn,  which  botanically  is  a  grass,  although  not  commonly  so 
called.  The  forage  supplied  by  these  plants  has  a  very  wide 
range  of  nutritive  value,  depending  on  a  variety  of  conditions. 
Chief  among  these  is  the  stage  of  maturity  at  which  the  crop 
is  utilized.  In  young,  growing  vegetation  the  cell  walls  are 
thin  and  consist  of  nearly  pure  cellulose,  while  the  cells  are 
filled  with  active  protoplasm  whose  chief  ingredients  are  pro- 
teins. Hence,  forage  cut  at  this  stage  shows  a  relatively  low 
percentage  of  crude  fiber  and  a  high  percentage  of  proteins. 
Young  and  tender  pasture  grass,  relatively  rich  in  protein  and 
low  in  crude  fiber,  may  even  approach  the  concentrates  in  value, 
as  illustrated  by  the  following  comparison  of  the  dry  matter  of 
a  sample  of  young  pasture  grass  with  that  of  average  oats :  — 

TABLE  162.  —  COMPARISON  OF  PASTURE  GRASS  AND  OATS 


PASTURE 

GRASS 

OA 

TS 

Percentage 
composition 

Digestible 
matter 

Percentage 
composition 

Digestible 
matter 

Ash     

Q  21 

•_ 

Crude  protein  .... 
Crude  fiber  ..... 
Nitrogen-free  extract 
Ether  extract   .... 

21.89 
18.25} 

.  44-39  j 
6.24 

13.42 
46.06 
3-59 

13.26 
(10.67} 
1  67.08] 
5-62 

10.39 

54.32 
4.70 

574 


NUTRITION  OF   FARM   ANIMALS 


As  the  plant  matures,  the  cell  walls  grow  thicker  and  be- 
come more  and  more  impregnated  with  tough,  woody  material. 
At  the  same  time,  more  soluble  carbohydrates,  as  starch  and 
sugar,  are  being  produced,  while  the  protoplasm  comes  to  oc- 
cupy but  a  small  part  of  the  cell.  The  fully  mature  forage, 
therefore,  is  rich  in  crude  fiber  of  a  tough,  resistant  sort,  contains 
much  carbohydrate  material  in  general  and  tends  to  be  poor  in 
proteins.  For  example,  three  samples  of  meadow-grass,  cut 
at  different  dates,  had  the  following  composition,  reduced  to  a 
uniform  percentage  of  water :  — 

TABLE  163.  —  COMPOSITION  OF  HAY  CUT  AT  DIFFERENT  DATES 


MAY  14 

JUNE  9 

JUNE  26 
(over-ripe) 

Water 

ICO 

I  C   O 

I  C  o 

Ash          .                        ... 

7-7 

6  8 

6  2 

Crude  protein   
Crude  fiber 

16.1 

21  O 

9-5 
20  6 

7.2 

72    A 

Nitrogen-free  extract      
Ether  extract    

37-3 
2.9 

36.8 
2.3 

36.9 
2-3 

IOO.O 

IOO.O 

IOO.O 

Accompanying  this  change  in  composition  goes  a  decrease  in 
digestibility.  In  the  first  place,  the  crude  fiber  becomes  more 
resistant  to  the  action  of  the  digestive  organs.  Furthermore, 
the  less  soluble  crude  fiber  seems  to  have  a  tendency  to  pro- 
tect the  contents  of  the  cells  from  digestion.  At  any  rate, 
the  percentage  digestibility  of  the  protein,  and,  to  a  less  de- 
gree, that  of  the  other  ingredients  also  suffers.  The  percentage 
digestibility  of  the  several  ingredients  of  the  above  samples  of 
grass,  omitting  the  ash,  was  found  to  be  as  follows :  — 

TABLE  164.  —  PERCENTAGE  DIGESTIBILITY  OF  HAY  CUT  AT  DIFFERENT 

DATES 


MAY  14 

JUNE  9 

JUNE  26 

Crude  protein   

73-3 

72.1 

55-5 

Crude  fiber 

70  ^ 

6c  7 

61  i 

Nitrogen-free  extract 

7q  7 

61.0 

ere.  7 

Ether  extract    

65-4 

51-6 

43-3 

THE  FEEDING  STUFFS 


575 


No  determinations  of  the  energy  values  of  these  samples  were 
made,  but  it  may  be  fairly  assumed  that  the  increasing  woodi- 
ness  not  only  diminished  the  total  amounts  of  digestible  nu- 
trients contained  but  also  increased  the  relative  expenditure  of 
energy  in  digestion  and  assimilation,  so  that  the  lesser  amount 
of  digestible  matter  in  the  more  mature  samples  was  probably 
less  valuable  per  unit  than  that  of  the  younger  samples. 

When  the  seeds  of  grasses  begin  to  form,  there  is  a  rather 
rapid  transfer  of  nutritive  materials  to  them  from  the  stalks 
and  leaves.  The  seeds  of  the  ordinary  hay  grasses,  however, 
are  so  small  and  so  well  protected  by  their  seed-coats  that  they 
either  shell  out  and  are  lost  or  largely  escape  mastication  and 
digestion.  Grass  harvested  after  the  seeds  have  formed  prac- 
tically furnishes  straw  rather  than  hay. 

680.  Maize.  —  A  somewhat  important  exception  to  the 
general  rule  regarding  the  influence  of  maturity  is  observed 
in  the  case  of  maize.  While  advancing  maturity  produces  its 
normal  effects  on  the  stalks  and  leaves,  such  large  amounts  of 
easily  digestible  material  are  stored  up  during  ripening  in  the 
grain,  and  the  latter  makes  up  so  large  a  percentage  of  the  total 
weight  of  the  crop,  that  it  outbalances  the  effect  of  increasing 
maturity,  and  the  ripe  or  nearly  ripe  crop,  taken  as  a  whole  — 
i.e.,  as  used  for  silage  or  as  field-cured  forage  —  is  more  di- 
gestible than  at  earlier  stages  of  growth.  For  example,  the 
dry  matter  of  maize  forage  at  three  different  stages  had  the 
following  composition  and  digestibility :  — 

TABLE  165.  —  COMPOSITION  AND  DIGESTIBILITY  OF  MAIZE   FORAGE  AT 
DIFFERENT  STAGES 


PERCENTAGE  COMPOSITION 

PERCENTAGE  DIGESTIBILITY 

Silking 

Kernels 
Glazing 

Nearly 
Mature 

Silking 

Kernels 
Glazing 

Nearly 
Mature 

Ash      

7-33 

3-57 

3-45 

— 

4.9 

34-8 

Protein      .... 

8.99 

7.08 

7.65 

58.8 

46.4 

63-1 

Non-protein  .     .     . 

4-77 

1.30 

0.47 

88.0 

79.6 

35-7 

Crude  fiber    .     .     . 

27.04 

16.88 

16.03 

67.7 

40.0 

47.2 

Nitrogen-free      .     . 

extract  .... 

48.28 

67-15 

68.69 

71.2 

76.8 

81.2 

Ether  extract     .     . 

3-59 

4.02 

3-71 

74-3 

84.8 

82.2 

Total  dry  matter    . 

IOO.OO 

IOO.OO 

IOO.OO 

64.2 

66.3 

72.6 

576 


NUTRITION  OF  FARM   ANIMALS 


On  the  other  hand,  of  course,  the  digestibility  of  the  stalks  and 
leaves  alone  (stover)  diminishes  as  in  the  case  of  other  grasses 
as  the  plant  grows  older. 

681.  Proportions  of  vegetative  organs.  —  The  composition 
and  digestibility  of  the  grasses  is  also  materially  affected  by  the 
proportions  of  the  various  vegetative  organs.  The  influence  of 
the  large  proportion  of  seed  in  the  maize  plant  has  already  been 
mentioned.  In  general,  the  leaves  of  the  grasses,  and  of  other 
forage  plants  as  well,  are  more  tender  and  contain  less  crude 
fiber  and  more  proteins  than  the  stems.  Leafy  species  and 
varieties  therefore  tend  to  have  a  higher  feeding  value  than 
those  which  consist  more  largely  of  stems,  and  any  influences, 
such  as  thickness  of  planting,  manuring,  season,  and  the  like, 
affecting  the  relative  proportion  of  leaves,  tend  also  to  affect 
the  value  of  the  crop.  The  combined  result  of  all  these  factors 
is  to  make  the  composition  of  grass,  or  of  the  hay  or  silage  made 
from  it,  extremely  variable.  American  analyses  of  timothy 
hay,  for  example,  show  total  protein  ranging  from  3.8  per  cent 
to  9.8  per  cent  and  fiber  varying  from  22.2  per  cent  to  38.5  per 
cent.  The  corresponding  variations  in  hay  from  a  few  other 
grasses  are  as  follows :  — 

TABLE  166.  —  PROTEIN  AND  FIBER  IN  VARIOUS  GRASSES 


TOTAL 
PROTEIN 

CRUDE 
FIBER 

Red-top      

Per  Cent 
c;.Q—  IO.4 

Per  Cent 
24.0—31.8 

Kentucky  blue-grass 

r  ?—  12  0 

17  7-26  8 

Meadow  fescue         

4.X—  II.  8 

20.8—^I.Q 

Orchard-grass      
M^aize  forage  l 

6.6-IO.4 
2  7—   6  0 

28.9-38.3 
7  ^—2A.7 

Oats       .          .          

Z  2—    Q.$ 

23.1—30.0 

That  these  variations  in  composition  are  accompanied  by  cor- 
responding differences  in  digestibility  has  already  been  pointed 
out.  Moreover,  the  percentage  of  crude  fiber  in  roughage 
appears  to  be  a  fairly  accurate  index  of  the  relative  expendi- 

1  Entire  plant,  usually  containing  considerably  more  water  than  hay. 


THE  FEEDING  STUFFS  577 

ture  of  energy  in  digestion  (770).  Not  only  does  coarse,  woody 
forage  contain  less  digestible  matter,  but  what  it  does  contain 
is  less  valuable  to  the  animal,  pound  for  pound,  than  that  de- 
rived from  forage  of  a  better  quality. 

682.  The  legumes  —  the  clovers,  alfalfa,  peas,  beans,  vetches, 
and  the  like  —  constitute  a  source  of  forage  second  only  to 
the  grasses   in   importance,  while   their   value   as  renovating 
crops  gives  them  a  peculiar  position  in  agriculture.     Broadly 
speaking,  leguminous  forage  may  be  said  to  differ  from  that 
of  the  grasses  in  two  main  points.     First,  under  like  condi- 
tions it  is  notably  richer  in  proteins  than  the  latter.     Second, 
there  is  a  more  marked  difference  between  the  physical  proper- 
ties of  the  stems  and  the  leaves  in  the  legumes,  the  rather  coarse 
stems  increasing  relatively  to  the  leaves  with  advancing  ma- 
turity.    Hay  from  somewhat  mature  legumes  is  therefore  likely 
to  be  bulky,  to  have  a  higher  percentage  of   crude  fiber  than 
grass  hay,  and  relatively  to  be  less  digestible.     For  the  same 
reason  it  is  more  subject  to  mechanical  losses  in  curing,  which 
likewise  lower  its  quality.     For  all  these  reasons,  the  compo- 
sition and  digestibility  of  leguminous  forage  show  an  even 
greater  range  than  those  of  the  grasses,  and  the  importance  of 
timely  cutting  is  still  more  marked.     In  brief,  the  influences 
which  affect  the  composition  and  digestibility  of  the  grasses 
affect  those  of  the  legumes  in  substantially  the  same  way  but 
to  an  even  greater  extent. 

683.  Straw  consists  of  the  vegetative  organs  of  the  plant 
after  the  removal  of  the  ripe  or  nearly  ripe  seeds.     Since  the 
ripening  of  the  seed  consists  largely  in  the  transfer  to  it  of  sol- 
uble materials  from  the  leaves  and  stems,  it  follows  that  the 
straw  will  be  poor  in  digestible  materials  in  proportion  to  the 
extent  of  seed  formation  and  the  degree  to  which  the  seeds 
ripen.     Furthermore,  those  parts  of  the  plant  most  distant  from 
the  seed  are  found  to  be  most  completely  exhausted  of  food 
material.     The  straw  of  the  common  small  grains  is  relatively 
very  poor  in  proteins  and  fat,  while  still  containing  not  incon- 
siderable amounts  of  digestible  carbohydrates  and  related  sub- 
stances.    Its  tough,  woody  character,  however,  as  indicated  by 
its  high  percentage  of  crude  fiber,  points  to  a  relatively  large 
expenditure  of  energy  in  its  digestion,  and  its  real  nutritive 
value  is  therefore  low.    Wheat  and  rye  straw  stand  at  the 

2  P 


578  NUTRITION  OF   FARM  ANIMALS 

foot  of  the  list,  while  oat  and  barley  straw  are  more  val- 
uable. Sheep  are  especially  adapted  to  utilize  straw,  consum- 
ing the  upper  and  more  valuable  parts  and  rejecting  the  coarser 
parts.  The  straw  of  maize  (stover)  constitutes  a  valuable 
feeding  stuff.  It  is  relatively  less  woody  than  that  of  the  small 
grains,  has  a  relatively  high  degree  of  digestibility,  and  is  more 
palatable  than  ordinary  straw.  To  secure  its  complete  con- 
sumption, however,  it  is  necessary  to  cut  or  shred  it,  and  it  has 
been  questioned  whether  the  additional  material  eaten  in  the 
cut  fodder  is  worth  the  labor  of  cutting.  The  straw  of  the 
legumes  is  richer  in  protein  than  that  of  the  cereals  and  lower 
in  fiber,  with  correspondingly  higher  digestibility.  On  the 
other  hand,  it  is  usually  coarse  and  unpalatable,  and  liable  to 
contain  molds  and  other  fungi. 

§  2.  ROOTS,  TUBERS  AND  FRUITS 

684.  Contain  much*  water.  —  Roots  and  tubers  constitute  a 
distinct  class  of  feeding  stuffs,  differing  markedly  in  their  prop- 
erties from  the  coarse  fodders  on  the  one  hand  and  the  con- 
centrated feeding  stuffs  on  the  other.     With  them  may  be  in- 
cluded for  convenience  certain  fruits,  notably  pumpkins  and 
other  cucurbita.     They  are  characterized  especially  by  their 
large  proportion  of  water.     In  the  root  crops  proper  (beets, 
turnips,  carrots,  mangels  and  the  like)  the  percentage  of  water 
may  vary  from  80  to  95.     The  tubers  (of  which  potatoes  are  the 
chief  representative)  contain  less  water,  the  range  being  ap- 
proximately 66  to  82  per  cent.     A  second  equally  marked  char- 
acteristic of  these  feeding  stuffs  is  the  low  percentage  of  crude 
fiber  in  their  dry  matter.     Their  percentage  of  crude  protein  is 
also  low,  and  a  large  share  of  it  consists  of  non-protein  of  in- 
ferior nutritive  value. 

685.  A  source  of  carbohydrates.  —  The  dry  matter  of  these 
crops  consists  largely  of  the  more  readily  soluble  carbohydrates. 
In  the  tubers  starch  is  the  predominant  carbohydrate,  while  in 
beets,  especially  sugar  beets,  cane  sugar  occupies  this  position, 
and  this  substance  has  been  shown  to  have  a  distinctly  lower 
nutritive  value,  for  ruminants  at  least,  than  starch.     In  other 
root  crops,  the  carbohydrates  consist  largely  of  gums,  pectin 
substances,  and  other  compounds,  including  the  pentose  car- 


THE  FEEDING  STUFFS  579 

bohydrates,  whose  exact  nutritive  value  is  still  uncertain. 
There  are  also  present  in  roots,  and  particularly  in  fruits, 
more  or  less  organic  acids  whose  nutritive  value  is  low.  In 
consequence  of  their  succulent  and  tender  nature,  tubers,  and 
especially  roots,  have  a  high  degree  of  digestibility  and  may  be 
presumed  to  require  little  energy  for  their  digestion.  They 
are  therefore  a  valuable  source  of  carbohydrate  material,  even 
though  some  of  their  ingredients  are  of  somewhat  inferior 
value.  In  general,  the  dry  matter  of  tubers  is  more  valuable 
than  that  of  roots.  On  the  other  hand,  the  dietetic  effects  of 
roots  are  especially  prized,  but  the  considerable  amount  of  labor 
required  for  their  cultivation  tends  to  restrict  their  use. 

§  3.  THE  CONCENTRATES 

686.  Comparison  with  roughage  and  with  roots.  —  The  con- 
centrated feeding  stuffs,  or  "  concentrates,"  as  their  name  im- 
plies, are  those  which  contain  a  large  amount  of  nutriment  in 
a  small  weight  and  bulk.     They  stand  in  contrast,  on  the  one 
hand,  with  roughage,  in  which  the  real  nutriment  is  accom- 
panied by  a  large  proportion  of  woody  fiber  and  other  indiges- 
tible matter  which  adds  to  the  weight  and  bulk  without  mate- 
rially increasing  the  nutritive  value.     On  the  other  hand,  they 
excel  the  roots  and  tubers  because,  while  the  dry  matter  of  the 
latter  is  very  valuable,  it  is  largely  diluted,  so  to  speak,  with 
water.     The  concentrates  are  therefore  the  main  reliance  for 
the  rapid,  intensive  production  of  meat,  milk  or  work.     The 
concentrates  may  be  subdivided  into  farm  products  and  the 
by-product  feeding  stuffs. 

Farm  products 

687.  The  cereal    grains.  —  The  grains  were,  until  compar- 
atively recent  times,  the  main  reliance  of  users  of  concentrates, 
and  indeed  are  still  in  many  sections  of  the  United  States. 
Corn,  oats,  barley,  rye,  peas,  beans,  rice  and  at  times  even 
wheat,  are  feeding  stuffs  whose  value  needs  no  advocate.     These 
seeds  contain,  stored  away  for  the  use  of  the  young  plantlet, 
proteins,  fats  and  carbohydrates  of  the  most  valuable  character 
and  "  representing  the  highest  type  of  vegetable  food."     Their 


580  NUTRITION  OF  FARM  ANIMALS 

nitrogenous  matter  is  chiefly  in  the  form  of  true  proteins  of 
recognized  nutritive  value,  their  carbohydrates  are  largely 
starch,  and  their  ether  extract  chiefly  true  fat.  Being  closely 
related  to  the  nutrition  of  the  young  plant,  the  composition  of 
the  properly  matured  seed  shows  much  smaller  variations  than 
that  of  the  coarse  fodders.  The  degree  of  maturity  of  the 
seed,  however,  materially  affects  its  composition  and  in  much 
the  same  way  as  it  does  that  of  the  coarse  fodders.  In  the 
early  stages  of  seed  formation,  the  protein  and  ash  flow  abun- 
dantly from  the  vegetative  organs  to  the  seed,  while  later  the 
ripening  of  the  seed  is  largely  an  accumulation  of  carbohydrates. 
Any  influences,  therefore,  which  check  the  normal  development 
of  the  seed,  such  as  drought  or  lodging  of  the  grain,  tend  to 
produce  a  seed  richer  in  protein  and  poorer  in  carbohydrates. 
Light,  shriveled  grain,  therefore,  tends  to  be  high  in  protein. 
Moreover,  the  ingredients  of  unripe  seeds  differ  to  a  consider- 
able extent  from  those  of  ripe  seeds.  The  nitrogen,  for  ex- 
ample, is  to  a  larger  extent  in  the  form  of  non-protein  rather 
than  true  protein,  and  the  carbohydrates  are  in  the  form  of  sugars 
of  one  sort  or  another  rather  than  starch,  as  in  the  ripe  grain. 
688.  Composition  and  digestibility  of  cereals.  —  The  cereal 
grains  are  characterized  by  a  medium  percentage  of  protein 
(8  to  14  per  cent),  chiefly  composed  of  true  protein,  a  rather 
low  percentage  of  fat  (1.5  to  6  per  cent)  and  a  high  percentage 
of  carbohydrates,  largely  starch.  Their  ash  is  small  in  amount 
and  in  it  potassium  and  phosphorus  acid  are  prominent,  while 
but  little  calcium  is  found.  Maize  contains  rather  less  protein 
than  the  other  cereal  grains,  with  correspondingly  high  percent- 
ages of  starch  and  of  fat.  While  it  has  been  shown  that  the 
protein  content  of  corn  can  be  notably  increased  by  selection  and 
breeding,  the  effects  of  the  latter  have  not  yet  sensibly  affected 
the  character  of  the  commercial  crop.  The  naked  grains  (maize, 
rye,  wheat)  show  a  comparatively  high  percentage  digestibility, 
and  both  in  this  respect  and  as  regards  their  composition  ex- 
hibit less  variation  than  the  hulled  grains  (oats,  barley).  In 
the  latter,  the  variable  proportion  of  the  relatively  valueless 
hulls  to  the  kernel  causes  both  composition  and  digestibility  to 
vary  greatly.  Oats,  for  example,  have  shown  the  extremes  of 
6  and  17  per  cent  protein  and  3  to  7  per  cent  of  fat.  The  hulls 
resemble  straw  in  composition  and  value.  They  therefore  in- 


THE  FEEDING  STUFFS  581 

crease  the  proportion  of  crude  fiber  in  the  grain,  and  corre- 
spondingly diminish  its  digestibility  and  nutritive  value. 

689.  Uses  of  cereals.  — The  place  of  the  cereal  grains  in  feed- 
ing practice  is  clearly  indicated  by  the  foregoing  statements. 
They  enable  the  feeder  to  introduce  into  his  rations,  without 
unduly  increasing  their  bulk  or  weight,  large  amounts  of  easily 
digestible  and  highly  nutritious  ingredients.     Of  themselves, 
they  contain  a  fair  proportion  of  protein  for  many  purposes, 
especially  for  mature   animals,  but   they  are  not  capable  of 
offsetting  a  deficiency  of  protein  in   the  other   ingredients  of 
the  ration,  nor  do  they  supply  enough  of  this  ingredient  to  meet 
fully  the  demands  of  the  rapidly  growing  animal  or  the  highly 
productive  dairy  cow. 

690.  Leguminous  grains.  —  The  leguminous  grains  share  the 
general  physical  properties  of  the  naked  cereal  grains,  and  like 
them  contain  feed  materials  (proteins,  carbohydrates,  fats)  of 
the  highest  grade.    They  are  especially  characterized,  in  con- 
trast with  the  cereal  grains,  by  their  relatively  high  percentage 
of  protein,  ranging  according  to  American   analyses   from  20 
to  42  per  cent.     Some  of  them,  as  the  soybean  and  the  lupine, 
also  carry  notable  amounts  of  fat,  but  the  more  common  ones 
are  not  richer  in  this  substance  than  the  cereals.    They  are 
richer  in  ash  than  the  cereals,  notably  as  regards  phosphoric 
acid  and  lime.    Their  digestibility  is  generally  high.    Like  the 
cereals,  they  are  valuable  as  sources  of  total  digestible  feed  in 
a  concentrated  form,  but  unlike  these  they  serve  also  to  enrich 
rations  in  protein.     Aside  from  certain  technical  by-products, 
they  are  the  most  available  materials  for  this  purpose,  and  the 
culture  of  leguminous  feeding  crops,  both  for  this  purpose  and 
for  their  effects  on  the  soil,  deserves  careful  consideration. 

691.  Oil  seeds.  —  The  oil  seeds,  such  as  flax,  cotton  and 
rape,  are  not  commonly  used  directly  as  feeding  stuffs  because 
of  their  commercial  value.    These  seeds  contain  a  high  per- 
centage of  protein,  while  in  place  of  much  of  the  carbohydrates 
of  the  cereals  and  legumes  a  large  percentage  of  oil  is  found. 
Flaxseed  contains  a  considerable  quantity  of  so-called  "  mu- 
cilage," which  swells  up  with  water  to  a  slimy  mass  and  has  a 
very  soothing  effect  on   the  digestive  organs.     Cottonseed  is 
fed  to  cattle  to  some  extent,  usually  either  boiled  or  roasted,  but 
is  regarded  as  dangerous  for  growing  swine. 


582 


NUTRITION  OF  FARM  ANIMALS 


By-products 

692.  Nature.  —  The  by-product  feeding  stuffs  are  the  resi- 
dues of  technical  processes  by  which  the  products  of  the  soil 
are  prepared  for  man's  use,  either  as  food  or  for  other  purposes. 
The  more  important  of  these  technical  processes  are :   the  mill- 
ing of  grains ;   the  manufacture  of  cereal  foods ;   the  manufac- 
ture of  alcoholic  liquors ;    the  manufacture  of  starch  and  glu- 
cose ;   the  manufacture  of  sugar ;  and  the  extraction  of  oils. 

693.  By-products  of  milling.  —  Milling  residues,  particularly 
of  wheat,  are  among  the  most  familiar  of  the  by-product  feed- 
ing stuffs.     They  include  the  screenings  secured  in  cleaning  the 
grain  for  milling  and  the  bran  and  middlings  secured  in  the 
grinding  proper.     The  screenings  are  an  exceedingly  variable 
mixture  according  to  the  quality  of  the  grain,  containing,  be- 
sides light  and  broken  grains,  a  great  variety  of  weed  seeds, 
fragments  of  straw,  sand  and  earth,  as  well  as  spores  of  numer- 
ous fungi,  and  dirt  of  all  sorts.     While  some  of  these  have  un- 
doubted feeding  value,  the  possible  danger  to  the  health  of  the 
animals,  and  of  the  infestation  of  the  fields  with  weed  seed 
through    the    manure,  demand  great  caution   in   the   use  of 

screenings  as  feed.  Its  ad- 
dition to  bran  or  middlings 
is  to  be  regarded  as  an 
adulteration. 

Bran.  —  The  bran  of  wheat 
or  rye  consists  essentially  of 
the  seed-coats  of  the  grain, 
the  layer  of  so-called  gluten 
cells  immediately  beneath 
them,  and  a  proportion  of 
the  inner,  floury  part  of  the 
grain  varying  with  the  per- 
fection of  the  milling.  The 
seed-coats  of  the  grain  con- 
tain most  of  its  crude  fiber, 
while  the  gluten  cells  are 
richer  in  proteins  than  the  inner  part  of  the  kernel.  In  pro- 
portion, therefore,  as  the  bran  is  more  perfectly  separated  from 
the  flour,  does  it  become  at  once  richer  in  protein  and  in  crude 


FIG.  43.  —  Partial  section  of  wheat  grain. 
(Bailey's  Cyclopedia  of  American  Agricul- 
ture.) 

i,  Seed  pod.  2,  Outer  seed  coat.  3,  Inner  seed 
coat.  4,  Gluten  cells.  5,  Starch  cells.  (Jordan.) 


THE  FEEDING  STUFFS  583 

fiber  and  poorer  in  easily  digestible  carbohydrates.  Such  bran 
is  more  valuable  as  a  source  of  protein  than  the  more  floury 
bran,  but  at  the  same  time  contains  less  total  digestible  mat- 
ter, and  probably  has  an  inferior  value  as  a  source  of  energy. 

Middlings,  as  the  name  indicates,  are  intermediate  products 
between  bran  and  flour.  In  modern  methods  of  milling,  va- 
rious grades  are  produced,  in  the  names  of  which  there  is  a 
considerable  lack  of  uniformity.  The  "  brown "  middlings 
contain  more  of  the  seed-coats  (bran)  than  the  "  white  "  mid- 
dlings, which  approach  the  low-grade  flour  ("  red  dog  "  flour) 
in  character.  Shorts  seem  to  be  substantially  the  same  as 
middlings.  Because  of  their  smaller  content  of  hulls,  mid- 
dlings are  decidedly  more  digestible  than  bjan,  while  scarcely 
inferior  to  it  in  percentage  of  protein. 

Buckwheat  middlings,  a  by-product  from  the  milling  of  buck- 
wheat, contains  nearly  twice  as  much  protein  and  fat  as  aver- 
age wheat  middlings,  and  correspondingly  less  carbohydrates. 
It  is  sometimes  called  buckwheat  bran,  but  this  name  is  also 
applied  to  the  tough,  innutritious  hulls  of  the  buckwheat,  which 
have  little  feeding-value  and  which  are  not  infrequently  used 
as  an  adulterant  of  the  middlings.  The  middlings  are  credited 
with  a  tendency  to  ferment  or  become  rancid  when  stored  in 
bulk,  and  also  with  producing  a  soft,  oily  butter-fat  when  fed 
in  large  amounts. 

Rice  bran  resembles  wheat  bran,  but  contains  less  protein 
and  fully  twice  as  much  fat.  The  pure  bran  is  sold  largely 
under  the  name  of  rice  meal,  while  the  commercial  bran  con- 
tains an  admixture  of  varying  amounts  of  rice  hulls.  The 
hulls,  which  are  separated  from  the  kernel  as  the  first  process 
in  the  milling,  contain  about  40  per  cent  of  fiber,  and  are  heavily 
impregnated  with  silica  and  covered  with  hard,  silicified  fibers 
which  are  liable  to  cause  severe  and  even  fatal  irritation  of  the 
digestive  organs.  Their  presence  in  the  bran  to  any  large 
extent  is  to  be  regarded  as  a  dangerous  adulteration. 

Rice  polish  results  from  the  polishing  of  the  rice  grains  after  the 
removal  of  the  bran  and  germ.  It  contains  somewhat  less  fat  and 
protein  than  the  pure  bran,  but  is  considerably  more  digestible. 

All  these  rice  by-products  contain  more  or  less  grits  or 
fragments  of  the  kernel,  which  have  been  found  to  be  rather 
difficult  of  digestion.  The  rice  products  are  also  rich  in  fat, 


NUTRITION  OF  FARM  ANIMALS 


which  becomes  rancid  rather  easily  and  often  renders  the  ma- 
terial unpalatable.  It  is  asserted  that  this  rancidity  can  be 
prevented  by  kiln-drying  the  bran  or  polish  as  soon  as  produced.. 
Uses  of  milling  by-products.  —  There  has  been  a  tendency 
to  regard  the  milling  by-products  largely  as  sources  of  protein. 
While  it  is  true  that  the  bran  and  middlings  are  richer  in  pro- 
tein than  whole  wheat  or  other  cereal  grains,  the  difference  is 
not  sufficient  to  enable  them  to  offset  to  any  marked  degree 
the  deficiencies  of  other  ingredients  of  the  ration  in  this  respect. 
They  are  to  be  regarded  primarily  as  sources  of  digestible 
matter  as  a  whole,  with  a  tendency  to  increase  somewhat  the 
proportion  of  protein  in  the  ration.  Familiarity  with  the  good 
qualities  of  wheat  bran  in  particular,  its  comparative  safety  as 
a  feed  in  inexperienced  hands,  and  its  good  dietetic  effect  have 
tended  to  an  exaggerated  idea  of  its  feed  value.  When  it  rules 
high  in  price  it  is  usually  possible  to  substitute  other  feeding 
stuffs  for  it,  partially  or  wholly,  which  will  furnish  both  pro- 
tein and  energy  more  cheaply.  Buckwheat  middlings,  on  the 

contrary,  often  furnish  a 
cheap  source  of  protein  for 
a  ration  otherwise  deficient 
in  it. 

694.  Breakfast  food  resi- 
dues. —  In  the  manufac- 
ture of  the  great  variety  of 
so-called  cereals,  or  break- 
fast foods,  now  on  the  mar- 
ket, a  considerable  quantity 
of  by-products  accumu- 
lates. In  the  case  of  the 
most  common  of  these, 
oatmeal,  the  residue  con- 
sists chiefly  of  the  hulls  of 
the  oats  together  with  some 
of  the  lighter  grains. 

Oat    hulls.— The    hulls 
FIG.  44- -  Partial  section  of  oat  grain,    themselves^  have    scarcely 

(Bailey's   Cyclopedia  of   American   Agricul-     more    feeding    value    than 

ture<)  the     straw,     which     they 

cen;.H^knS)edcoat>4>GIutencells-  S(Starch    resemble    in    composition, 


THE  FEEDING   STUFFS  585 

while  the  proportion  of  light  oats  is  not  sufficient  mate- 
rially to  raise  the  value.  Oat  hulls  are  rarely  offered  as  such 
in  the  market  but  are  usually  disposed  of  in  one  of  two 
ways.  First,  they  are  made  the  basis  of  various  proprietary 
feeds,  cheap  by-products  of  various  sorts  being  added,  usually 
including  a  small  amount  of  the  protein-rich  by-products  shortly 
to  be  described.  These  feeds  are  offered  under  various  names 
and  with  abundant  advertising  testimonials.  While  they  are 
by  no  means  worthless,  it  is  evident  that  the  oat  hulls  themselves 
are  no  more  valuable  because  of  the  addition  to  them  of  other 
materials,  while  the  consumer  ultimately  pays  the  cost  of  mix- 
ing, transportation  and  advertising.  The  second  use  to  which 
oat-hulls  are  put  is  the  adulteration  of  the  mixed  feeds,  es- 
pecially corn  and  oat  feeds,  which  are  freely  offered  on  the 
market.  Since  it  is  difficult  to  recognize  even  a  considerable 
adulteration  of  this  sort,  such  mixed  feeds  should  be  purchased 
only  from  manufacturers  of  known  integrity  or  under  a  satis- 
factory guarantee  as  to  purity. 

Barley  feed,  a  by-product  of  the  manufacture  of  pearled 
barley,  is  similar  in  feeding  value  to  oat  hulls. 

Hominy  feed.  —  In  the  manufacture  of  hominy  from  corn, 
the  hull,  the  germ  and  the  more  starchy  parts  of  the  kernel  are 
rejected  and  constitute  hominy  feed,  or  hominy  chop,  which 
is  similar  to  the  whole  kernel  in  composition  and  digestibility, 
except  that  its  percentage  of  fat  is  greater.  Consequently  it 
has  a  somewhat  higher  feeding  value,  although  the  fat  is  likely 
to  become  rancid  on  long  keeping  and  thus  lower  its  quality. 

695.  By-products  of  the  fermentation  industries.  —  The 
manufacture  of  alcoholic  liquors  consists  essentially  in  the 
conversion  of  the  starch  of  grains  or  potatoes  into  sugar  and 
the  subsequent  fermentation  of  this  sugar  by  means  of  yeast. 
The  resulting  liquor  may  be  consumed  directly  (beer,  ale)  or 
it  may  be  distilled,  yielding  the  more  concentrated  distilled 
liquors  or  commercial  alcohol. 

M alt  sprouts.  —  The  first  step  in  the  process  is  the  prepa- 
ration of  malt,  by  allowing  moistened  barley  to  germinate. 
The  growth  of  the  sprouts  is  stopped  by  drying  when  they 
are  about  one-third  inch  long,  and  these  dried  sprouts,  sepa- 
rated from  the  grain,  constitute  malt  sprouts.  Being  young 
roots  of  barley,  they  have  the  general  properties  of  all  young 


586  NUTRITION  OF  FARM  ANIMALS 

plant  growth,  containing  a  high  percentage  of  nitrogen,  much  of 
it  in  the  form  of  non-protein,  and  a  low  percentage  of  crude  fiber. 

Brewers'  grains.  —  The  next  step  in  the  process  is  the  mash- 
ing of  the  ground  malt  and  other  grain  with  warm  water.  In 
this  process,  the  diastase  of  the  sprouted  barley  acts  on  the 
starch  of  the  grain,  transforming  it  into  sugar.  In  the  manu- 
facture of  beer  or  ale,  the  resulting  liquid  is  drawn  off  and  fer- 
mented separately,  leaving  a  residue  known  as  brewers'  grains, 
which  is  used  extensively  as  a  dairy  feed.  In  the  fresh  state  it 
is  valuable,  but  is  subject  to  the  disadvantage  of  fermenting  or 
souring  very  readily,  and  tending  in  this  state  to  injure  the 
quality  of  the  milk.  Somewhat  recently,  economical  pro- 
cesses for  drying  it  have  been  perfected,  and  the  dried  brewers' 
grains  constitute  a  valuable  feed  which  can  be  shipped  like 
any  other  dried  feed. 

Distillers'  grains.  —  In  the  preparation  of  distilled  liquor  or 
alcohol,  the  liquid  is  fermented  in  contact  with  the  grains  and 
the  alcohol  then  distilled  off,  leaving  a  residue  known  as  dis- 
tillers' grains  or  distillery  slop.  This  residue  is  much  wetter 
than  brewers'  grains,  but  is  less  subject  to  fermentation,  since 
the  sugar  has  been  more  completely  removed.  Large  quantities 
of  it  are  now  put  on  the  market  in  the  dried  form,  both  under 
its  own  name  and  various  trade  names,  some  of  which  contain 
no  suggestion  of  the  real  nature  of  the  material.  It  constitutes 
a  valuable  source  of  stock  feed.  The  grains  produced  from  rye 
are  regarded  as  the  poorest  and  those  from  maize  as  of  the  best 
quality. 

In  all  these  processes  the  object  is  to  convert  the  starch  of 
the  grain  as  completely  as  possible  into  sugar  and  then  into 
alcohol.  This  results  in  increasing  the  percentage  of  all  the  other 
ingredients  in  the  residues.  They  contain  accordingly  a  high 
percentage  of  protein  with  also  a  somewhat  greater  percentage 
of  crude  fiber  than  the  ordinary  grains.  They  serve,  therefore, 
not  only  to  supply  digestible  matter  as  a  whole  but  also  to 
correct  a  deficiency  of  protein  in  the  ration. 

696.  By-products  of  oil  extraction.  —  The  extraction  of  com- 
mercial oils  from  various  oil-bearing  seeds  leaves  by-products, 
called  oil  cake  or  oil  meal,  some  of  which  have  a  high  feeding 
value.  Of  these,  cottonseed  and  linseed  meal  are  the  only  ones 
extensively  used  in  the  United  States  and  are  typical  of  the 


THE  FEEDING  STUFFS  587 

others.  The  seeds  of  cotton  and  flax  are  rich  in  both  fat  and 
protein.  Hulled  cottonseed  contains  about  30  per  cent  of  each 
and  flaxseed  about  22  per  cent  protein  and  35  per  cent  fat,  the 
latter  percentage,  however,  being  somewhat  variable.  The  oil 
is  extracted  from  the  seeds  either  by  pressure  or  by  the  use  of 
solvents,  leaving  a  residue  still  containing  some  fat  and  very 
rich  in  protein. 

Cottonseed  meal.  —  At  present  cotton  oil  is  extracted  only  by 
pressure,  the  resulting  hard  cake  being  ground  to  cottonseed 
meal.  The  highest  grade  of  cottonseed  meal  is  made  from  the 
hulled  seed  and  contains  40  to  44  per  cent  of  crude  protein  and 
8  to  9  per  cent  of  fat.  It  should  be  nearly  free  from  the  hulls 
and  therefore  contain  little  crude  fiber.  Cottonseed  meal  is 
adulterated  extensively  with  the  tough,  black  hulls  of  the 
cottonseed,  which  have  a  very  low  feeding  value.  This  is  es- 
pecially true  of  the  inferior  grades  of  commercial  cottonseed 
meal,  which  are  sold  at  a  lower  price  than  the  standard  grade. 

Linseed  meal.  —  Linseed  oil  is  extracted  from  the  flaxseed  both 
by  pressure  and  by  means  of  naphtha,  the  latter  being  com- 
pletely removed  from  the  resulting  oil-meal  and  recovered  for 
use  again.  The  "  new  process  "  of  extraction  removes  the  fat 
more  completely  than  the  "  old  process  "  of  pressure,  and  the 
resulting  linseed  meal  is  somewhat  poorer  in  fat  and  contains 
somewhat  more  protein  than  the  old-process  meal.  The  pro- 
cess of  extraction  by  pressure  has  been  so  far  perfected  in  recent 
years,  however,  that  the  difference  between  the  old-process  and 
new-process  meal  is  distinctly  less  than  formerly.  The  protein 
of  the  new-process  meal  appears  to  be  slightly  less  digestible 
than  that  of  the  old-process  meal,  which  tends  still  further  to 
reduce  the  difference  between  the  two. 

Other  oil  meals.  —  Oils  are  also  manufactured  commercially 
from  the  seeds  of  the  common  peanut,  the  soybean,  the  oil 
palm  and  the  cocoa  palm.  The  resulting  oil  cakes  or  meals  are 
extensively  used  as  feeding  stuffs  in  European  countries  but  do 
not  appear  to  have  as  yet  found  access  to  the  feed  market  of 
the  United  States  to  any  considerable  extent. 

The  corn-germ  meal  mentioned  in  connection  with  the  gluten 
feeds  may  also  be  classed  as  an  oil-meal. 

697.  By-products  of  starch  and  glucose  manufacture.  — 
Starch  and  glucose  are  made  in  the  United  States  chiefly  from 


588 


NUTRITION  OF  FARM  ANIMALS 


maize.  The  starch  is  separated  by  coarse  grinding  and  the 
use  of  water,  the  starch  being  carried  off  in  suspension  and  al- 
lowed to  settle  out.  Glucose  is  manufactured  by  further  treat- 
ment of  the  starch  with  acid.  In  the  preparation  of  the  starch, 
the  parts  of  the  kernel  which  are  rejected  are  the  hull,  the  germ 

and  the  more  glutinous  part 
of  the  interior  of  the  grain 
from  which  the  starch  cannot 
be  completely  separated. 

Corn  (maize)  bran.  —  The 
hulls  are  comparatively  low 
in  protein  and  contain  con- 
siderable fiber.  When  sold 
separately  they  are  called 
corn  bran,  although  the  com- 
position of  commercial  sam- 
ples indicates  some  admix- 
ture of  the  germs. 

FIG.  45.  —  Partial  section  of  maize  kernel.  Germ    meal.  —  The     germ 

(Bailey's  Cyclopedia  of  American  Agricul-      contains   about   30  per   Cent 

of   oil,   which   has   a   com- 

i.  Outer  layer  of  skin.     2,  Inner  layer  of  skin.  -11  i  •  i 

4,  Gluten  cell.    5.  Starch  cells.     (Jordan.)  merCial   Value  and  IS  SCCUred 

by  pressing  the  germs.  The 

residue  constitutes  germ  meal,  which  still  contains  about  7 
per  cent  of  oil,  and  in  the  neighborhood  of  n  per  cent  of  crude 
protein. 

Gluten  meal  and  feed.  —  The  glutinous  residue  of  the  kernel 
constitutes  gluten  meal,  containing,  in  general,  30  to  40  per 
cent  of  crude  protein  with  a  comparatively  low  percentage  of 
fat  and  fiber.  Some  factories  mix  the  gluten  meal  and  the  hulls, 
and  sell  the  mixture  under  the  name  of  gluten  feed,  which  con- 
tains approximately  24  per  cent  of  crude  protein,  6  per  cent  of 
crude  fiber  and  6  per  cent  of  fat.  Sometimes  the  hulls  and 
germs  are  sold  together  under  the  names  "  sugar  feed  "  or  "  starch 
feed,"  either  wet  or  dry.  In  fact,  various  mixtures  of  the  three 
main  products  are  made  and  sold  under  diverse  commercial 
names.  These  various  glucose  products  should  invariably 
be  purchased  on  a  guarantee  as  regards  composition  and  purity. 

698.  By-products  of  sugar  manufacture.  —  Sugar  has  come  to 
be  manufactured  from  sugar-beets  to  a  considerable  extent  in 


THE  FEEDING   STUFFS  589 

the  United  States,  while  in  certain  regions  the  manufacture 
from  sugar  cane  is  an  important  industry. 

Sugar-beet  pulp.  —  The  sugar  is  extracted  from  the  finely 
cut  beets  by  means  of  water  in  what  is  known  as  the  diffusion 
process.  The  residue  from  this  constitutes  what  is  commonly 
known  as  beet  pulp,  which  is  essentially  sugar  beets  minus  the 
sugar  and  some  of  the  other  soluble  substances.  In  the  fresh 
state  it  contains  90  to  95  per  cent  of  water,  which  may  be  re- 
duced to  about  85  to  87  per  cent  by  pressing.  Its  general 
properties  are  similar  to  those  of  roots  and  it  occupies  much  the 
same  place  in  the  ration.  Its  digestible  matter  consists  chiefly 
of  carbohydrates  belonging  to  the  group  of  pectins  and  gums, 
somewhat  inferior  to  the  sugar  of  the  beets  but,  according  to 
recent  investigation,  fully  as  valuable  as  the  digestible  matter 
of  mangels.  The  wet  beet  pulp  is  too  heavy  to  bear  long  trans- 
portation, but  may  be  preserved  in  the  neighborhood  of  the 
factory  by  ensiling.  It  is  now,  however,  dried  and  put  on  the 
market  as  dried  beet  pulp,  containing  not  more  than  5  to  10 
per  cent  of  water.  The  dried  pulp  is  relatively  about  equally 
valuable  with  the  wet  pulp,  especially  if  soaked  in  water,  as  it 
should  be  before  feeding. 

Molasses.  —  In  the  further  manufacture  of  sugar  either  from 
sugar  beets  or  sugar  cane,  there  remains,  as  a  final  residue,  the 
molasses.  This  contains  20  to  25  per  cent  of  water,  approxi- 
mately 50  per  cent  of  sugar,  scarcely  more  than  one-half  per 
cent  of  true  protein,  and  8  to  10  per  cent  of  non-protein,  along 
with  other  substances  of  doubtful  nutritive  value.  It  is  essen- 
tially a  source  of  easily  soluble  carbohydrates,  principally 
sugar.  Beet  molasses,  in  particular,  has  a  marked  laxative 
action,  commonly  ascribed  to  the  potassium  salts  present  in  it 
but  perhaps  due  quite  as  much  to  the  sugar.  For  this  reason, 
care  is  required  to  accustom  animals  to  it  gradually  and  not  to 
overfeed  with  it.  Its  laxative  qualities  are  said  to  be  valuable 
when  used  in  small  amounts  for  horses  in  preventing  attacks  of 
colic. 

Molasses  feeds.  —  Owing  to  its  physical  properties,  molasses 
is  an  inconvenient  material  to  handle.  To  avoid  this  difficulty, 
the  so-called  molasses  feeds  have  been  put  on  the  market. 
These  consist  of  molasses  dried  down  on  some  suitable  material. 
A  large  number  of  concentrated  feeding  stuffs  have  been  used 


5QO  NUTRITION  OF   FARM  ANIMALS 

for  this  purpose,  and  it  has  also  been  dried  together  with  the 
beet  pulp,  forming  molasses  pulp.  All  these  feeds  are  of  value 
in  proportion  to  the  materials  out  of  which  they  are  made. 

699.  By-products  of  the  packing  house.  —  The  slaughtering 
of  meat  animals  on  a  large  scale  in  the  modern  packing  house 
yields  a  number  of  highly  nitrogenous  by-products  which  are  of 
especial  value  in  the  feeding  of  swine  and  poultry. 

Dried  blood  is  especially  rich  in  protein,  of  which  it  contains 
over  80  %,  practically  all  of  which  is  digestible.  It  contains  a 
small  amount  of  fat  and  but  little  ash. 

Tankage  consists  essentially  of  the  residue  left  after  the 
rendering  of  the  meat  scraps,  trimmings  and  scrap  bones  of 
the  packing  house.  Tankage  contains  much  less  protein  than 
dried  blood  but,  on  the  other  hand,  contains  a  considerable  per- 
centage of  fat,  while  the  bone  which  it  contains  renders  it  rela- 
tively rich  in  ash  ingredients,  especially  calcium  and  phos- 
phorus. As  is  obvious  from  the  method  of  its  manufacture, 
tankage  is  likely  to  vary  widely  in  composition  and  should 
always  be  bought  on  a  guarantee. 


CHAPTER  XVI 
RELATIVE   VALUES    OF    FEEDING   STUFFS 

As  soon  as  live  stock  husbandry  emerged  from  the  pastoral 
stage  and  man  began  to  store  up  forage  for  the  winter  or  to 
utilize  the  products  of  his  cultivated  land  for  feeding  his  do- 
mestic animals,  the  question  of  the  relative  values  of  the  dif- 
ferent feeding  stuffs  necessarily  arose.  As  agriculure  has 
gradually  become  more  intensive  and  as  the  variety  of  natural 
materials  and  of  technical  by-products  available  has  increased, 
the  question  has  grown  in  importance,  the  traditions  of  prac- 
tice based  on  the  experience  of  earlier  investigations  have  been 
recognized  to  be  insufficient  guides,  and  much  effort  has  been 
put  forth  to  replace  these  traditions  by  exact  knowledge. 

§  i.  DIRECT  COMPARISONS  OF  FEEDING  STUFFS 

700.  Hay  values.  —  A  natural  and  logical  method  of  inves- 
tigation was  to  feed  the  materials  in  question  to  animals  and 
compare  the  amount  of  increase  or  of  milk  which  was  secured. 
Good  meadow  hay  was  universally  regarded  as  a  complete  feed, 
suitable  for  practically  all  purposes.  Hence  it  was  naturally 
taken  as  the  standard  and  the  effort  was  made  to  establish  from 
the  results  of  experience  and  experiment  what  amounts  of  dif- 
ferent feedstuffs  would  replace  a  unit  weight  of  hay.  In  this 
way  arose  the  tables  of  so-called  hay  values.1  The  first  of  these 
was  that  published  by  Thaer  in  Germany  in  1809,  based  chiefly 
on  the  early  chemical  analyses  of  Einhof  in  which  the  con- 
stituents soluble  in  water,  alcohol,  dilute  acids  and  dilute  alka- 
lies were  determined.  The  sum  of  all  these  ingredients,  with- 
out distinction  as  to  kind,  was  taken  to  represent  the  nutritive 
value,  and  the  hay  values  were  computed  in  proportion  to  them. 

1  Compare  Henneberg,  Uber  den  Heuwert  der  Futterstoffe ;  Beitrage  zu  Fiitter- 
ung  der  Wiederkauer,  Heft  i,  1860,  pp.  1-16;  and  von  Gohren,  Naturgesetze  der 
Fattening,  1872,  pp.  286-305. 

59  ! 


5Q2  NUTRITION  OF  FARM  ANIMALS 

The  system  had  the  advantage  of  simplicity.  Experience  had 
afforded  a  fairly  definite  idea  of  the  quantity  of  hay  required 
for  a  given  amount  of  production.  It  was  only  necessary  to 
compute  from  the  hay  values  what  weights  of  the  available 
feeding  stuffs  would  produce  equal  effects.  The  simplicity  of 
the  calculations,  due  especially  to  the  fact  that  the  relative 
value  of  a  feed  was  expressed  by  a  single  fixed  number,  led  to 
a  rapid  adoption  of  the  system.  "  To  each  feeding  stuff  a  defi- 
nite hay  value  was  assigned  and  in  a  short  time  one  had  a 
beautiful  table  constructed  which  gave  the  most  exact  infor- 
mation regarding  the  value  of  the  most  diverse  feeding  materials 
in  comparison  with  hay.  Anything  which  appeared  in  any  way 
suited  for  feeding  found  its  place  in  the  table  and  each  new 
feeding  stuff  which  the  progress  of  agronomy  provided,  directly 
or  indirectly,  was  likewise  quickly  incorporated.  It  went  so 
far  that  even  the  salt  supplied  to  the  animals  was  computed  in 
hay  values."  l 

Thaer  himself  based  his  figures  in  part  on  the  results  of  prac- 
tical experiments.  Numerous  subsequent  investigators  carried 
out  direct  comparisons  of  feeding  stuffs  on  an  extensive  scale 
and  not  one  but  several  tables  of  hay  values  were  formulated. 
Unfortunately,  these  tables  differed  widely  from  each  other, 
some  of  them  giving  two  or  three  times  as  great  a  hay  value  as 
another  to  the  same  feed.  It  was  evident  also  that  the  un- 
limited substitution  of  different  classes  of  feeds,  as  for  instance 
of  grain  or  roots  for  hay,  was  impossible.  Such  discrepancies 
and  limitations  led  to  various  modifications  of  the  methods  of 
estimating  the  hay  values.  Boussingault  regarded  the  protein 
content  of  the  feed  as  the  principal  factor,  while  Nathusius  took 
into  account  also  the  content  of  crude  fiber  and  Wolff  z  worked 
out  a  somewhat  elaborate  method  in  an  attempt  to  retain  the 
convenience  of  reckoning  with  a  single  number  for  a  feed.  The 
impossibility  of  this,  however,  gradually  came  to  be  recognized, 
and  the  hay  values  have  now  only  a  historical  interest. 

701.  Practical  feeding  trials.  —  But  while  the  system  of 
hay  values  has  become  obsolete  the  idea  of  determining  the 
relative  nutritive  values  of  feeding  stuffs  on  the  basis  of  direct 
comparisons  of  the  results  obtained  in  practice  has  survived  in 

1  Settegast,  Die  Fiitterungslehre,  1879,  p.  4. 

2  Die  landwirtschaftliche  Fiitterungslehre,  1861,  pp.  455-456. 


RELATIVE  VALUES  OF  FEEDING  STUFFS  593 

full  vigor.  A  very  considerable  share  of  the  investigations  in 
stock  feeding  during  the  last  two  decades,  especially  perhaps  in 
the  United  States,  has  consisted  of  experiments  intended  to 
determine  the  effects  of  the  substitution  of  one  feed  for  another 
in  a  ration. 

Undoubtedly  the  so-called  practical  trial  has  an  important 
part  to  play  in  the  development  of  a  sound  theory  of  feeding  as 
well  as  in  relation  to  the  economic  aspects  of  the  subject.  Re- 
garded, however,  simply  as  a  means  for  the  quantitative  deter- 
mination of  the  relative  values  of  feeding  stuffs  it  is  subject  to 
precisely  the  same  limitations  and  uncertainties  as  the  old  at- 
tempt to  determine  hay  values,  and  in  this  respect  has  in 
general  led  to  scarcely  more  satisfactory  or  concordant  results. 
It  is  as  true  in  the  later  as  in  the  earlier  experiments  that 
the  effect  of  a  feeding  stuff  may  vary  widely  with  the  com- 
bination in  which  it  is  fed  and  the  conditions  under  which 
it  is  used. 

702.  Feed  units.  —  An  interesting  attempt  to  revive  the 
fundamental  conception  of  hay  values  in  a  modified  form  and 
within  a  restricted  field,  and  thus  to  retain  the  advantage  of 
expressing  the  relative  value  of  a  feed  by  a  single  number, 
is  found  in  the  so-called  feed  unit  system  devised  by  Fjord 
and  his  associates  in  Denmark  and  extensively  used  also  in 
Sweden.1 

The  feed  unit  system,  like  that  of  hay  values,  is  essentially  a 
system  of  empirical  equivalents  according  to  which  feeding 
stuffs  may  replace  each  other.  Instead  of  hay,  the  basis  of 
comparison  is  a  unit  weight  of  grain  (corn,  barley,  wheat  or 
rye  or  a  mixture  of  grains).  This  is  called  a  feed  unit  and  the 
amounts  of  other  feeds  required  to  equal  the  feed  unit  have 
been  determined  in  very  extensive  cooperative  feeding  experi- 
ments by  the  group  system  (572)  with  swine  and  especially  with 
dairy  cows.  The  experiments  themselves  have  been  executed 
with  every  precaution  to  ensure  accuracy.  The  results  for 
dairy  cows,  as  revised  by  Woll  for  American  feeding  stuffs, 
and  the  Danish  values  for  swine  and  for  the  horse  are  given  by 
Henry  and  Morrison 2  as  follows :  — 

1  For  a  more  complete  discussion  of  the  feed  unit  system  compare  Woll ;  Wis- 
consin Expt.  Sta.,  Circular  No.  37. 

2  Feeds  and  Feeding,  isth  Edition,  p.  127. 

2Q 


594 


NUTRITION  OF   FARM   ANIMALS 


TABLE  167.  —  AMOUNT  OF  DIFFERENT  FEEDS  REQUIRED  TO  EQUAL  ONE 

FEED  UNIT1 


FEED 


FEED  REQUIRED  TO 
EQUAL  i  UNIT 


Average 


Range 


FOR   DAIRY  COWS 

Concentrates 

Corn,  wheat,  rye,  barley,  hominy  feed,  dried 
brewers'  grains,  wheat  middlings,  oat  shorts, 
peas,  molasses  beet  pulp,  dry  matter  in  roots  . 

Cottonseed  meal 

Oil  meal,  dried  distillers'  grains,  gluten  feed,  soy- 
beans   

Wheat  bran,  oats,  dried  beet  pulp,  barley  feed, 
malt  sprouts 

Alfalfa  meal,  alfalfa  molasses  feeds 

Hay, and  straw 

Alfalfa  hay,  clover  hay 

Mixed  hay,  oat  hay,  oat  and  pea  hay,  barley  and 
pea  hay,  red-top  hay 

Timothy  hay,  prairie  hay,  sorghum  hay      .     .     . 

Corn  stover,  stalks  or  fodder,  marsh  hay,  cut  straw 
Soiling  crops,  silage  and  other  succulent  feeds 

Green  alfalfa 

Green  corn,  sorghum,  clover,  peas  and  oats,  can- 
nery refuse 

Alfalfa  silage 

Corn  silage,  pea  vine  silage 

Wet  brewers'  grains 

Potatoes,  skim  milk,  buttermilk    .     .     .     .     .     . 

Sugar  beets 

Carrots 

Rutabagas 

Field  beets,  green  rape 

Sugar  beet  leaves  and  tops,  whey 

Turnips,  mangels,  fresh  beet  pulp 

The  value  of  pasture  is  generally  placed  at  8  to  10 
units  per  day,  on  the  average,  varying  with 
kind  and  condition  .  .... 


i.o 

0.8 

0.9 
i.i 

1.2 
2.0 
2-5 

3-o 
4.0 

7.0 

8.0 

S-o 

6.0 
4.0 
6.0 
7.0 
8.0 
9.0 

IO.O 
12. 0 
12-5 


2.0-    3.0 

2-5-  3-5 
3-5-  6.0 

6.0-  8.0 
7.0-10.0 
5.0-  7.0 


8.0-10.0 


10.0-15.0 


1  The  values  for  pigs  and  horses  are  those  given  in  the  Danish  valuation  table 
and  those  for  dairy  cows  the  values  as  revised  by  Woll  for  American  feeding  stuffs 
in  Wisconsin  Circular,  No.  37. 


RELATIVE  VALUES  OF  FEEDING  STUFFS 


595 


TABLE  167.  —  AMOUNT  OF  DIFFERENT  FEEDS  REQUIRED  TO  EQUAL  ONE 
FEED  UNIT  (Continued) 


FEED 

FEED  RE 
EQUAL 

QUIRED  TO 

i  UNIT 

Average 

Range 

FOR  PIGS 

Indian  corn,  barley,  wheat,  oil  cakes      .... 
Rye  wheat  bran               

I.O 
I  4. 

— 

Boiled  potatoes  

4.O 



Skim  milk 

6  0 

Whey    ...                   .              ... 

12  O 



FOR   HORSES 

One  pound  of  Indian  corn  equals  one  pound  of 
oats  or  one  pound  of  dry  matter  in  roots     .     . 

703.  Logical  basis  of  feed  unit  system.  —  The  Scandinavian 
feed  unit  values  have  a  broad  experimental  basis.  The  re- 
sults of  the  experiments  have  been  reasonably  consistent 
and  in  general  the  feed  unit  values  correspond  well  with  the 
relative  net  energy  values  discussed  in  the  following  chapter 
except  that  they  ascribe  somewhat  higher  values  to  protein- 
rich  feeds. 

Nevertheless,  the  logical  basis  of  the  system  has  the  same 
defect  that  is  inherent  in  all  such  systems.  As  was  shown  in 
Chapter  V  (263),  feed  has  two  distinct  functions  and  these  func- 
tions are  incommensurable.  It  is  as  impossible  to  combine  the 
value  of  a.feed  as  a  source  of  protein  or  other  structural  material 
with  its  value  as  a  source  of  energy,  and  to  express  the  result  in 
a  single  number,  as  it  is  to  compare  the  relative  values  of  food 
and  water  to  a  starving  man.  A  protein-rich  feed  like  cotton- 
seed meal,  for  example,  will  necessarily  produce  a  greater  effect 
when  added  to  a  ration  deficient  in  protein  than  when  added 
to  one  containing  an  abundance  of  that  ingredient;  with  a 
material  deficient  in  protein  precisely  the  reverse  would  be  true. 
As  a  matter  of  fact  the  feed  units  are  only  claimed  to  be  equiva- 
lent values,  "  under  ordinary  conditions  of  feeding  these  animals, 
when  fed  in  mixed  rations  that  would  contain  over  a  certain 


596  NUTRITION  OF  FARM  ANIMALS 

minimum  of  digestible  protein." 1  As  Henry  and  Morrison  have 
pointed  out,  "  The  feed  unit  system  has  been  evolved  in  a  com- 
paratively small  region  where  similar  crops  are  grown  on  the 
different  farms  and  the  price  of  purchased  feeds  does  not  vary 
widely  throughout  the  district." 

704.  Comparison  of  feed  units  and  net  energy  values.  — 
The  writer  is  not  able  to  agree  with  those  who  would  introduce 
the  feed  unit  system  in  this  country  with  its  wide  variety 
of  feeding  stuffs  and  conditions.  The  applicability  of  the  feed 
units,  as  just  pointed  out,  is  conditioned  upon  the  presence 
of  sufficient  protein  in  the  rations.  As  thus  limited,  however, 
they  practically  attempt  to  measure  the  relative  values  as  sources 
of  energy,  and  for  this  purpose  the  use  of  the  net  energy  values 
to  be  considered  in  the  next  chapter  is  just  as  simple  arithmeti- 
cally and  equally  accurate,  while  it  has  two  immense  advantages. 
First,  the  net  energy  values  are  rational  and  not  empirical  values. 
They  are  based  on  physiological  investigations  and  their  very 
imperfections  tend  to  stimulate  further  investigation  which  may 
lead  to  their  great  improvement  or  to  the  discovery  of  new  and 
still  better  methods  of  comparison.  The  feed  unit,  on  the  other 
hand,  constitutes  a  dead  end  so  far  as  investigation  is  concerned, 
leading  to  nothing  beyond  some  increase  in  numerical  accuracy, 
while  it  is  far  inferior  in  pedagogic  value.  Second,  the  feed 
units  are  purely  relative  values,  based  on  direct  comparisons  of 
the  results  with  different  materials  with  no  attempt  to  discover 
the  causes  of  the  observed  differences.  They  show  to  what 
extent  one  feeding  stuff  is  better  or  worse  than  others,  but  es- 
tablish no  relation  between  feed  and  product.  Energy  values,  on 
the  other  hand,  aim  to  show  the  amount  of  product  which  may 
be  expected  from  a  unit  weight  of  the  feeding  stuff  -r-  i.e.,  the 
amount  of  energy  which  it  can  contribute  to  the  maintenance 
of  the  body  or  to  the  building  up  of  new  tissue.  Thus,  if  aver- 
age maize  meal,  for  example,  has  an  energy  value  of  85  Therms 
per  hundred  pounds,  this  means  that  one  hundred  pounds  of  it, 
fed  as  part  of  a  maintenance  ration,  would  conserve  in  the  body 
of  the  animal  an  amount  of  fat  and  protein  having  an  energy 
value  of  85  Therms,  which  would  otherwise  be  burned  up  to 
support  the  vital  activities.  Furthermore,  it  means  that,  if 
added  to  the  maintenance  ration,  the  maize  will  furnish  ma- 

1  Woll,  loc.  cit.  p.  13. 


RELATIVE  VALUES  OF  FEEDING  STUFFS  597 

terial  sufficient  to  produce  a  quantity  of  milk  or  of  meat  having 
an  energy  value  of  85  Therms.  Still  further,  the  investigations 
by  which  these  facts  are  established  also  show  that  out  of  the 
approximately  187  Therms  gross  energy  of  100  pounds  of  maize 
meal,  about  50  escape  unused  in  the  various  excreta,  while  about 
52  are  expended  in  the  various  processes  connected  with  the 
consumption  and  assimilation  of  the  feed.  In  other  words,  they 
show  the  nature  of  the  losses  suffered  as  well  as  the  final  amount 
of  product  to  be  expected.  Such  data  as  these  have  an  inde- 
pendent value  and  are  of  an  entirely  different  nature  from  those 
expressed  in  the  feed  units. 

§  2.  RELATIVE  VALUES  BASED  ON  COMPOSITION  AND 
DIGESTIBILITY 

705.  Chemical  composition.  —  Even  before  the  rise  of  the 
system  of  hay  values,  attempts  were  made  by  Davy,  Einhof, 
Sprengel  and  others  to  compare  feeding  stuffs  on  the  basis  of 
chemical  analyses,   and  indeed   the   earlier  hay  values  were 
based  in  part  on  such   comparisons  (700).     The  methods  for 
the  chemical  analysis  of  feeding  stuffs  were  gradually  improved, 
although  they  still  remain  quite  imperfect,  but  along  with  this 
improvement  came  a  clearer  recognition  of  the  fact  that  the 
problem  of  relative  values  is  at  bottom  a  physiological  and  not 
a  chemical  question. 

706.  Physiological   functions   of   nutrients.  —  In   particular 
the  teachings  of  Liebig  and  the  investigations  of  Bischoff  and 
Voit l  on  the  nutrition  of  carnivora  served  to  establish  those 
basal  facts  regarding  the  functions  of  proteins,  carbohydrates, 
fats  and  ash  in  nutrition  which  have  been  confirmed  and  ex- 
tended by  later  inve*stigations  and  have  been  outlined  in  Chap- 
ter V.     Haubner  appears  to  have  been  the  earliest  to  suggest  the 
application  of  these  principles  to  comparisons  of  feeding  stuffs 
and  the  feeding  of  farm  animals,  while  to  Grouven  2  belongs  the 
credit  of  having  first  formulated  the  requirements  of  animals 
and  the  values  of  feeding  stuffs  in  terms  of  the  different  classes 
of  nutrients.     His  tables,  however,  were  based  on  the  total 
nutrients  found  by  chemical  analysis  and  were  comparatively 

1  Gesetze  der  Ernahrung  des  Fleischfressers,  1860. 

2  Vortrage  uber  Agriculturchemie,  1858. 


598 


NUTRITION  OF   FARM   ANIMALS 


soon  replaced  by  more  accurate  data  based  on  determinations  of 
the  digestible  nutrients. 

707.  Henneberg's  and  Stohmann's  investigations.  —  It  is  to 
the  fundamental  investigations  of  Henneberg  and  Stohmann  1 
Sit  the  Weende  Experiment  Station,  near  Gottingen,  that  we 
are  indebted  for  the  inauguration  of  a  system  of  comparing  the 
values  of  feeding  stuffs  which  has  endured  with  little  material 
change  up  to  the  present  time.  These  investigators  were  the 
first  to  apply  systematically  in  studying  the  nutrition  of  herbiv- 
ora  the  physiological  principles  already  demonstrated  for  other 
classes  of  animals  and  to  base  their  determinations  upon  the 
outgo  as  well  as  upon  the  income  of  the  body.  Their  earlier 
experiments  deal  chiefly  with  the  digestibility  of  feeding  stuffs 
and  rations.  Later  a  comprehensive  scheme  of  investigation, 
including  determinations  of  the  gaseous  excreta,  was  laid  out 2 
and  begun  but  never  completed. 

TABLE  168.  —  EXAMPLE  OF  COMPUTATION  OF  DIGESTIBLE  NUTRIENTS 


CLOVER  HAY 

MAIZE  MEAL 

Chemical  composition 
Water      
Ash                                       .     .     . 

iS-03 
5-49 

13-73 
1.25 

Protein 

10.24 

8.80 

Non-protein      
Crude  fiber  
Nitrogen-free  extract      
Ether  extract   

1.36 
28.61 
36.98 
2.29 

0.25 
1.89 

70.44 
3-64 

Percentage  digestibility 
Ash     
Protein    
Non-protein      ....          ... 
Crude  fiber  

IOO.OO 

46.48% 
53.19% 

100.00% 

50.27%             0 

IOO.OO 

18.40% 

66.43% 

100.00% 

32.40% 

Nitrogen-free  extract      .          ... 
Ether  extract 

68.94% 

65.02% 

97-75% 
95-74% 

Digestible  nutrients 
Ash     .    .                   

5.49  X  0.4648  =    2.55% 

1.25  X  0.1840  =    0.23% 

Protein 

10.24  X  0.5319  =    5.45% 

8.80  X  0.6643  =    5.85% 

i  36  X  i  ooo    =    1.36% 

0.25  X  i.  ooo    =    0.25% 

Crude  fiber 

28  61  X  0.5027  =  14.38% 

1.89  X  0.3240  =    0.61% 

Nitrogen-free  extract      
Ether  extract    

36.98  X  0.6894  =  25.49% 
2.29  X  0.6502  —    1.49% 

70.44  X  0.9775  =  68.85% 
3.64  X  0.9574  =    3-48% 

1  Beitrage  zur  Begrundung  einer  rationellen  Fiitterung  der  Wiederkauer,  1860 
and  1864. 

J  Neue  Beitrage,  etc.,  1870. 


RELATIVE  VALUES  OF  FEEDING  STUFFS 


599 


708.  The  digestible  nutrients.  —  The  methods  of  digestion 
experiments  as  used  by  Henneberg  and  Stohmann  and  modified 
by  later  experimenters  were  outlined  in  Chapter  III  (157-161). 
A  vast  number  of  determinations  of  digestibility  have  been 
made,  upon  a  great  variety  of  materials,  and  the  results  have 
served  as  the  basis  for  computing  the  relative  values  of  feeding 
stuffs.  The  method  of  comparison  may  be  illustrated  by 
means  of  the  digestion  experiment  on  clover  hay  and  maize 
meal  used  in  Chapter  III  to  illustrate  the  method.  (Table  168.) 

Simplified  statement.  —  Since  the  digestible  crude  fiber  and 
digestible  nitrogen-free  extract  have  been  shown  (168,  169)  to 
have  the  elementary  composition  of  starch,  they  have  been 
commonly  added  together  and  called  carbohydrates.  Con- 
sidering the  digestible  ether  extract  to  be  substantially  fat, 
and  omitting  the  ash  on  the  assumption  that  an  average 
ration  contains  a  sufficient  supply,  the  amounts  of  the  three 
principal  groups  of  digestible  nutrients  may  be  stated  more 
concisely  as  follows :  — 


TABLE  169.  —  SIMPLIFIED  STATEMENT  OF  DIGESTIBLE  NUTRIENTS 


CLOVER 
HAY 

MAIZE 
MEAL 

Digestible  protein     

r  4r% 

r.8c% 

Digestible  non-protein 

I  l6  % 

O   2Z  °7n 

Digestible  carbohydrates  

30  87% 

60  4.6% 

Digestible  fats      

1.4.0  % 

3.48% 

This  statement  may  be  still  further  simplified.  A  pound 
of  fat  produces  when  burned  about  2.25  times  as  much  heat  as 
the  same  weight  of  carbohydrates.  The  non-proteins  have  ap- 
proximately the  same  heat  value  as  the  carbohydrates,  while 
it  is  still  questioned  whether  they  help  to  build  up  protein  tis- 
sue. By  multiplying  the  digestible  fat  by  the  factor  2.25  and 
adding  the  digestible  carbohydrates  and  non-protein  we  obtain 
the  carbohydrate  equivalent  for  the  digestible  matter  other 
than  protein  and  the  digestible  nutrients  may  be  expressed  in 
the  following  still  more  concise  form :  — 


600  NUTRITION  OF  FARM  ANIMALS 

TABLE    170.  —  DIGESTIBLE  NUTRIENTS  REDUCED  TO  CARBOHYDRATE 
EQUIVALENT 


CLOVER 
HAY 

MAIZE 
MEAL 

Digestible  protein 

r  AC% 

*  8<c% 

Digestible  carbohydrates  equivalent  to   non-nitrog- 
enous nutrients     

44-S8  % 

77-54% 

Total  nutrients       

TO  O3  °7n 

81  10% 

709.  T-he  nutritive  ratio.  —  By  the  method  just  illustrated 
the  content  of  a  feeding  stuff  in  digestible  matter  is  expressed 
by  two  numbers  which  correspond  to  the  two  functions  of  the 
nutrients  already  described  (263) .     The  digestible  protein  shows 
what  the  feeding  stuff  can  contribute  towards  the  structural 
needs  of  the  body,  while  the  carbohydrate  equivalent  of  the 
digestible  non-nitrogenous  nutrients  shows  what  portion  of  the 
digestible  nutrients  can  serve  only  as  a  source  of  fat  or  of  energy. 
The  ratio  between  these  two  quantities  gives  a  useful  indication 
as  to  whether  a  feeding  stuff  or  mixture  of  feeding  stuffs  is  suited 
for  forms  of  production  like  growth  or  milk  production,  which 
require  a  considerable  supply  of  protein,  or  whether  it  is  better 
adapted  for  those  which,  like  work  or  fattening,  make  special 
demands  for  fuel  material.     This  so-called  "  nutritive  ratio  " 
(better,  nutrient  ratio)  is  obtained  by  a  simple  proportion.     Thus 
in  the  two  instances  just  given,  it  is  computed  as  follows,  the 
second  half  of  the  proportion  constituting  the  nutritive  ratio :  — 

For  clover  hay,  5.45  :  44.58  =  i :    8.2 
For  maize  meal  5.85  :  77.54  =  i :  13.3 

710.  Significance  of  results.  —  Under  the  stimulus  of  Hen- 
neberg  and  Stohmann's  pioneer  work  and  under  the  leadership 
of  Wolff,  investigation  of  the  digestibility  of  feeding  stuffs 
was  actively  taken  up  in  Germany  and  later  in  the  United 
States  and  other  countries,  and  as  the  result  of  much  labor  ex- 
pended during  the  last  fifty  years  a  fairly  complete  knowledge 
of  the  amounts  and  proportions  of  the  digestible  nutrients  sup- 
plied by  most  of  the  ordinary  feeding  stuffs  has  been  accumu- 
lated.    Extensive  tables  of  averages  have  been  published  by 


RELATIVE  VALUES  OF  FEEDING  STUFFS  6oi 

various  authors,  including  many  of  the  agricultural  experiment 
stations,  and  it  is  an  easy  matter  for  the  feeder  to  learn  what 
amounts  and  kinds  of  digestible  nutrients  any  given  feed  or 
ration  will  supply. 

In  view  of  the  extensive  use  of  such  tables  it  is  important 
that  the  exact  significance  of  the  results  which  they  embody 
should  be  understood.  As  a  mere  matter  of  logical  concep- 
tion, the  comparison  of  feeding  stuffs  on  the  basis  of  their 
digestible  nutrients  is  inferior  to  that  based  on  hay  values  or 
on  feed  units.  In  these  methods  the  attempt  is  made,  how- 
ever crudely,  to  compare  the  actual  effects  produced  by  the 
feeding  stuffs  in  the  animal  body.  A  determination  of  diges- 
tibility, on  the  contrary,  affords  no  direct  information  whatever 
as  to  the  nutritive  effect  of  the  materials  digested.  It  is  not 
even  necessary  to  weigh  the  animal  in  a  digestion  trial.  The 
comparison  of  feeding  stuffs  on  this  basis  is  between  what  they 
contain  and  not  between  what  they  accomplish. 

Nevertheless,  tables  of  digestible  nutrients  have  been  of  great 
value  in  promoting  more  rational  and  profitable  feeding,  but  it 
is  becoming  increasingly  evident  that  they  express  but  part  of 
the  truth.  The  essential  feature  of  the  newer  methods  of 
comparison  outlined  in  this  volume  is  not  that  they  employ 
units  of  energy  as  a  basis  of  comparison  but  that  they  con- 
stitute a  return  to  the  logical  conceptions  which  were  at  the 
basis  of  the  early  methods  and  which  were  discussed  in  so  il- 
luminating a  manner  by  Henneberg  and  Stohmann  in  the 
introduction 1  to  their  "  Neue  Beitrage "  in  1870.  These 
newer  methods  seek  to  determine,  by  more  elaborate  and 
accurate  methods  than  were  available  to  the  earlier  experiment- 
ers, the  actual  effect  of  the  feed  on  the  body  of  the  animal  as 
well  as  its  content  of  matter  and  energy. 

§  3.  CONDITIONS  AFFECTING  DIGESTIBILITY 

711.  Digestibility  variable.  —  Not  only  is  the  current  method 
of  estimating  the  relative  values  of  feeding  stuffs,  as  described  in 
the  previous  section,  based  largely  on  the  digestibility  of  the  ma- 
terials in  question,  but  the  latter  is  also  a  most  important  fac- 

1  Uber  das  Ziel  und  die  Methode  der  auf  den  landwirtschaftlichen  Versuchs- 
stationen  auszufuhrenden  thier-physiologischen  Untersuchungen. 


602  NUTRITION  OF   FARM   ANIMALS 

tor  in  determining  the  actual  production  values  discussed  in  the 
next  chapter,  since,  as  there  shown  (742),  the  excretion  in  the 
feces  constituted  the  greatest,  although  not  the  only,  loss  of 
chemical  energy  suffered  by  the  feed. 

The  percentage  digestibility  of  a  feeding  stuff  or  of  its  several 
constituents,  however,  has  not  a  fixed  and  invariable  value, 
analogous  to  the  solubility  of  a  chemical  compound,  but  may  be 
affected  more  or  less  by  a  variety  of  conditions,  although  to  a 
less  extent  than  is  frequently  supposed.  This  arises  from  the 
fact  noted  in  Chapter  III  (155)  that  portions  of  ingredients 
capable  per  se  of  solution  and  resorption  in  the  digestive  tract 
actually  escape  digestion  for  various  reasons  and  reappear  in 
the  feces.  Any  conditions  which  influence  the  digestibility  in 
this  way,  however,  necessarily  affect  the  value  of  the  feeding 
stuff  by  whichever  method  determined,  and  the  more  impor- 
tant of  them  may  be  conveniently  considered  in  this  connection. 

The  conditions  which  affect,  or  which  are  supposed  to  affect, 
the  degree  of  completeness  with  which  the  potentially  digestible 
ingredients  of  a  feeding  stuff  are  actually  digested  may  be  di- 
vided into  those  relating  to  the  animal  itself  and  those  relating 
to  the  feed. 

Conditions  relating  to  the  animal 

712.  Variation  at  different  times.  —  An  important  fact, 
which  must  be  borne  in  mind  in  studying  the  influences  of 
various  factors  upon  digestion,  is  that  the  percentage  digesti- 
bility of  the  same  feeding  stuff  by  the  same  individual  has  been 
found  to  vary  more  or  less  at  different  times. 

This  has  been  shown  especially  by  G.  Kiihn.1  In  experiments 
upon  the  digestibility  of  meadow  hay  by  cattle  the  variations  in  the 
percentage  digestibility  of  the  dry  matter,  which  is  the  one  least  sub- 
ject to  error,  ranged  from  0.6  to  2.1,  averaging  1.3,  and  the  digestibility 
of  the  organic  matter  showed  about  the  same  variations.  That  for 
the  nitrogen-free  extract  averaged  1.8,  while  in  the  case  of  the  crude 
fiber,  protein  and  ether  extract  it  reached  3.3.  These  variations  were 
shown  to  be  materially  larger  than  the  possible  errors  of  experiment. 
Similar,  although  relatively  somewhat  smaller,  variations  were  ob- 
served on  rations  of  hay  and  bran.  Moreover,  Kiihn  points  out  that 
the  maximum  differences  were  found  in  those  cases  in  which  the  larger 

1  Landw.  Vers.  Stat,  29  (1883),  129,  147  and  153- 


RELATIVE  VALUES  OF  FEEDING  STUFFS  603 

number  of  single  trials  were  made.  No  connection  could  be  traced 
between  the  variations  in  digestibility  and  the  condition  of  the  animals. 

The  writer  1  observed  a  similar  difference  in  two  experiments  upon 
one  sheep  with  clover  hay  while  the  other  sheep  of  the  pair  showed 
no  significant  difference.  In  later  experiments  2  in  which  the  feces 
of  three  steers  were  quantitatively  collected  daily  for  periods  of  56 
and  27  days  on  identical  rations,  it  was  shown  that  the  digestibility 
of  the  air  dry  matter  3  and  nitrogen  computed  from  overlapping  ten- 
day  periods,  varied  at  times  from  the  average  for  the  whole  experi- 
ment by  amounts  greater  than  the  estimated  experimental  error. 
Mumford,  Grindley,  Hall  and  Emmett  4  likewise  observed  distinct 
fluctuations  in  the  digestion  coefficients  obtained  with  cattle  in  suc- 
cessive weekly  periods  following  preliminary  periods  of  from  two  to 
four  weeks. 

All  the  foregoing  experiments  were  upon  dry  feed  and  the  writer 
is  inclined  to  attribute  them,  to  a  considerable  degree  at  least,  to  irreg- 
ular voiding  of  the  feces. 

713.  Species.  —  The  differences  in  the  anatomy  of  the  di- 
gestive organs  of  different  species  might  naturally  be  expected 
to  result  in  differences  in  the  extent  to  which  the  feed  of  these 
species  is  digested.     This  is  true  especially  of  those  ingredients 
of  the  feed  whose  so-called  digestibility  is  due  to  the  action  of 
organized  ferments  and  which,  therefore,  will  be  more  or  less 
dependent  upon  the  opportunities  which  the  digestive  tract 
affords  for  the  stagnation  of  the  feed  and  so  for  the  activity 
of  these  organisms. 

714.  Species  of  ruminants.  —  Few    direct    comparisons    of 
the  digestibility  of  the  same  feeding  stuff  by  different  species 
of  ruminants  are  on  record.     In  view  of  the  similarity  of  the 
alimentary  canal  in  these  species,  one  would  naturally  expect 
to  find  comparatively  small  differences  in  the  extent  to  which 
identical  feeding  stuffs  are  digested.     In  a  general  way  this 
expectation  is  borne  out  by  the  average  results  of  a  large  number 
of  recorded  digestion  experiments  upon  feeds  bearing  the  same 
name,  although  not  of  identical  composition.       Thus  Wolff,5 
in  1874,  compared  the  results  of  about  40  German  experiments 

1  Amer.  Jour,  of  Science,  28  (1885),  368. 
2Penna.  Expt.  Sta.,  Bui.  42  (1898),  pp.  129-141. 

3  The  daily  excretion  of  dry  matter  was  not  determined  and  there  is  a   possi- 
bility of  a  small  error  due  to  lack  of  exact  uniformity  in  the  air  drying. 

4  Ills.  Expt.  Sta.,  Bui.  172  (1914)-  6  Landw.  Futterungslehre. 


604  NUTRITION  OF  FARM   ANIMALS 

on  cattle  and  sheep  and  Jordan  and  Hall l  have  made  similar 
comparisons  of  nine  American  experiments. 

On  the  basis  of  comparisons  of  this  sort  it  has  been  generally 
considered  that  digestion  coefficients  obtained  with  one  species 
of  ruminants  may  be  applied  to  others  without  material  error 
and  the  sheep  or  goat  has  been  the  favorite  experimental  an- 
imal. Such  direct  evidence  as  is  available,  however,  leads  to 
some  modification  of  this  conclusion. 

Comparisons  of  the  digestive  powers  of  cattle  and  sheep  for 
identical  feeding  stuffs  have  been  reported  by  Frear,2  the  Missis- 
sippi Station,3  Bartlett,4  Kellner,5  Tangl  and  Weiser,6  Zuntz,7 
and  Voltz.8  . 

The  experimental  results,  while  not  extensive  and  not  al- 
together consistent,  seem,  when  taken  in  connection  with  the 
general  comparisons  previously  made,  to  warrant  the  conclu- 
sion that  as  regards  the  better  grades  of  roughages  the  differ- 
ence in  digestive  power  between  cattle  and  sheep  is  not  marked 
and,  with  the  exception  of  Zuntz's  rather  remarkable  results, 
the  same  would  seem  to  be  the  case  as  regards  concentrates. 
On  the  other  hand,  it  would  appear  that  in  the  case  of  the  coarser 
and  less  digestible  forms  of  forage  a  distinct  difference  exists  in 
favor  of  cattle.  Kellner  is  inclined  to  ascribe  this  difference  to 
the  greater  percentage  of  water  in  the  contents  of  the  lower 
intestine  of  cattle  as  compared  with  sheep,  which  favors  a  more 
extensive  action  of  the  organized  ferments. 

715.  The  horse  compared  with  ruminants.  —  A  number  of 
comparisons  have  been  made  of  the  digestibility  of  identical 
feeding  stuffs  by  horses  and  by  sheep  as  representing  ruminant 
animals.  The  most  extensive  trials  of  this  sort  were  made  by 
Wolff9  in  Hohenheim  from  1877  to  1884  but  Tangl  and  Weiser10 
have  also  compared  the  digestibility  of  several  samples  of 
hay  by  horses  and  by  sheep  or  cattle  and  Langworthy11  has 
compiled  the  results  of  a  large  number  of  digestion  experiments 

1  U.  S.  Dept.  Agr.,  Office  Expt.  Stas.,  Bui.  77  (1900),  90. 

2  Penna.  Expt.  Sta.,  Rep.  1890,  58.  3  Eighth  Rpt.  (1895),  79. 

4  Maine  Expt.  Sta.,  Bui.  no  (1904).  6Landw.  Vers.  Stat.,  63  (1906),  313. 

6Landw.  Jahrb.,  35  (1906),  205. 

7  Jahrb.  Ver.  Spiritus  Fabrikanten  in  Deutschland,  XII  (1912),  324. 

8  Landw.  Jahrb.,  45  (1913),  422. 

9  Grundlagen  fur  die  rationelle  Fiitterung  des  Pferdes,  1886. 
10  Landw.  Jahrb.,  35  (1905),  159. 

"  U.  S.  Dept.  Agr.,  Office  Expt.  Stas.,  Bui.  125,  p.  44. 


RELATIVE  VALUES  OF   FEEDING   STUFFS  605 

TABLE  171.  —  DIGESTIBILITY  BY  SHEEP  AND  BY  HORSES 


NUMBER 

OF 

EXPERI- 
MENTS 

PERCENTAGE  DIGESTIBILITY 

Dry 

Mat- 
ter 

Organic 
Matter 

Crude 
Pro- 
tein 

Crude 
Fiber 

Nitro- 
gen- 
free 
Extract 

Ether 
Ex- 
tract 

ROUGHAGE 

Wheat  straw  l 
Sheep                   

2 
2 

7 
4 

8 
4 

10 
6 

2 
I 

8 
5 

12 

6 

13 

8 

6 
6 

2 
I 

2 

I 

2 

I 

45 
2O 

57 
47 

56 

47 

62 
50 

65 

54 

55 
5i 

58 
58 

70 
66 

87 
85 

88 

77 

00 

OO 
71 

88 
90 

48 
23 

59 

47 

59 
48 

64 
5i 

76 
62 

56 
5i 

59 
58 

7i 
68 

90 
87 

90 

80 

88 

72 

88 
9i 

54 
57 

57 
57 

65 
62 

73 
69 

56 
56 

7i 
73 

80 
86 

87 
86 

89 

83 

88 
^4 

79 
78 

59 

27 

68 
39 

56 
36 

63 
42 

80 
57 

50 
37 

45 
40 

30 

21 

79 
65 

66 
8 

97 
5i 

62 

100 

37 
18 

62 
56 

62 

55 

65 

57 

76 
66 

61 
63 

66 
70 

76 

74 

9i 
93 

93 
89 

78 
5i 

9i 
94 

46 
23 

51 
24 

54 
20 

65 
13 

56 
29 

4i 
14 

83 
7i 

84 
13 

75 

7 

78 
27 

85 
63 

Horse                                      • 

Meadow  hay  —  inferior 

Horse                            .          . 

Meadow  hay  —  average 
Sheep    
Horse             .    . 

Meadow  hay  —  superior 
Sheep    
Horse                       .     . 

Dried  pasture  grass 
Sheep 

Horse             

Red  clover  hay 
Sheep 

Horse    .     

Alfalfa  hay 
Sheep 

Horse    

Oats 
Sheep         

Horse    .     .    .    .    .    .    .  *  . 

Beans 
Sheep    . 

Horse    

Peas 
Sheep    
Horse                  . 

Lupins 
Sheep 

Horse         

Maize 
Sheep 

Horse    

Results  regarded  by  Wolff  as  of  questionable  accuracy. 


606  NUTRITION  OF   FARM  ANIMALS 

on  both  horses  and  ruminants.  The  results  of  Wolff's  com- 
parisons are  contained  in  Table  171. 

In  general,  the  comparisons  have  shown  a  distinct  superiority 
of  ruminants  over  horses  in  the  digestion  of  roughages,  especially 
as  regards  those  ingredients  (crude  fiber  and  nitrogen-free  ex- 
tract) whose  so-called  digestion  is  wholly  or  in  part  a  fermenta- 
tion. Even  in  the  better  grades  of  forage  the  crude  fiber  was 
on  the  whole  considerably  less  digestible  by  horses  than  by 
ruminants,  although  three  of  Tangl's  experiments  are  excep- 
tions, while  less  difference  appears  as  regards  the  nitrogen-free 
extract  and  scarcely  any  as  regards  the  crude  protein.  On  the 
other  hand,  little  difference  was  observed  in  most  cases  in  the 
digestibility  of  the  total  organic  matter  and  nitrogen-free  extract 
of  concentrates.  In  the  latter  the  digestibility  of  the  crude 
fiber  was  also  relatively  low  but  in  view  of  its  small  amount  and 
the  consequent  uncertainty  in  the  results  little  significance 
attaches  to  this  difference.  The  notably  lower  figures  for  the 
digestibility  of  the  ether  extract  by  horses  arise  in  all  probability 
from  a  larger  excretion  of  ether-soluble  excretory  products 
in  the  feces  of  these  animals  rather  than  from  any  real  differ- 
ence in  digestibility. 

716.  Swine  compared  with  ruminants.  —  Comparisons  of 
the  digestibility  of  identical  feeds  by  swine  and  by  sheep  have 
been  reported  by  Honcamp,  Neumann  and  Milliner,1  the  feed- 
ing stuffs  being  wheat,  rye  and  the  by-products  of  their  milling. 
Although  the  results  upon  the  individual  animals  of  the  same 
species  fluctuated  somewhat,  as  is  not  unusual  (718),  the  aver- 
age results  showed  no  material  superiority  on  the  part  of  either 
species. 

Owing  to  the  small  percentage  of  crude  fiber  contained  in  the 
feeds,  the  results  upon  this  ingredient  are  naturally  quite  variable 
and  of  no  especial  significance.  Aside  from  this,  there  seems  to  have 
been  a  slight  superiority  on  the  part  of  the  swine  in  the  case  of  the 
rye  products  (with  the  exception  of  the  germ),  while  with  the  wheat 
products  the  reverse  was  the  case,  especially  with  the  coarser  milling 
products.  The  swine  seem  to  have  digested  the  crude  protein  fully 
as  well  as  the  sheep  in  all  the  experiments. 

Fingerling,  Bretsch,  Losche  and  Arndt,2  in  experiments  de- 
signed especially  to  test  the  relative  digestive  powers  of  sheep  and 

1  Landw.  Vers.  Stat.,  81  (1913),  205.  zlbid.,  83  (1913),  181. 


RELATIVE  VALUES  OF  FEEDING  STUFFS 


607 


swine  for  crude  fiber,  added  straw  pulp,  young  grass  and  wheat 
chaff  to  basal  rations.     Their  average  results  were  as  follows :  — 

TABLE  172.  —  DIGESTIBILITY  BY  SHEEP    AND  BY  SWINE 


NITRO- 

DRY 
MAT- 
TER 

GANIC 

MAT- 

CRUDE 
PRO- 
TEIN 

CRUDE 
FIBER 

GEN- 
FREE 
EX- 

ETHER 
EX- 
TRACT 

TRACT 

Straw  pulp 

% 

% 

% 

% 

% 

% 

Sheep       

72.65 

73-19 

— 

77.27 

72.23 

— 

Swine 

IOI  22 

88  85 

04.  8  1 

62.  7C 

Grass 

Sheep  

65.29 

69.77 

76.85 

69.49 

67.29 

66.93 

Swine 

4Q  ^8 

51  86 

-2  QC 

2.O  ^Q 

<2  O7 

84.  2.  C 

Wheat  chajf 

Sheep 

4O   22 

4.6  Q3 

r  r  ^5 

2O  3.4. 

f  I   r^i 

Swine  . 

20  53 

22  CK 



27  86 

The  amount  of  straw  pulp  added  to  the  basal  ration  was  com- 
paratively small,  so  that  the  results  on  this  material  are  sub- 
ject to  relatively  large  errors  (161),  but  the  conclusion  seems 
indicated  that  pure  cellulose,  freed  from  encrusting  matter,  can 
be  readily  digested  by  swine,  and  this  conclusion  is  fully  sup- 
ported by  the  later  determinations  of  Fingerling,  Kohler  and 
Reinhardt.1  For  the  crude  fiber  of  ordinary  feeding  stuffs, 
on  the  contrary,  the  digestive  power  of  the  swine  was  decid- 
edly inferior  to  that  of  the  sheep. 

A  general  idea  of  the  relative  digestive  power  of  swine  and 
ruminants  may  also  be  gained  by  a  comparison  of  the  average 
results  obtained  for  the  two  species  on  feeding  stuffs  of  the  same 
name  although  not  of  identical  composition,  as  shown  by  com- 
pilations like  those  by  Kellner  2  and  by  Henry  and  Morrison.3 

The  recorded  results  do  not  indicate  that  there  is  any  material 
difference  between  swine  and  ruminants  as  regards  their  di- 
gestive power  for  concentrates.  As  in  the  case  of  the  horse, 
there  seems  to  be  a  tendency  toward  a  lower  percentage  diges- 
tibility of  ether  extract  by  swine,  due  most  likely  to  the  presence 

1  Landw.  Vers.  Stat.,  84  (1914),  149. 

2  Ernahrung  landw.  Nutztiere,  6th  Ed.,  p.  45. 
1  Feeds  and  Feeding,  isth  Ed.,  pp.  647-652. 


6o8 


NUTRITION  OF   FARM   ANIMALS 


of  more  ether-soluble  excretory  products  in  the  feces  of  these 
animals.  The  figures  for  the  crude  fiber  of  concentrates  are 
also  materially  lower  with  swine  in  some  cases,  but  in  others 
equal  to  or  even  higher  than  those  obtained  for  ruminants.  In 
view  of  the  small  percentage  of  crude  fiber  in  the  concentrates 
and  the  corresponding  range  of  possible  error,  however,  the 
results  on  this  point  are  of  little  significance.  The  crude  fiber 
of  roughage  is  but  imperfectly  digested  by  swine.  Crude  pro- 
tein would  appear,  on  the  whole,  to  be  rather  more  completely 
digested  by  swine  than  by  ruminants,  possibly  indicating  the 
presence  of  more  nitrogenous  excretory  products  in  the  feces 
of  the  latter. 

717.  Fowls  compared  with  swine.  —  Owing  to  the  difficulty 
of  collecting  the  feces  of  fowls  separately  from  the  urine,  com- 
paratively few  determinations  upon  these  animals  have  been 
made.  Bartlett,1  who  has  reported  a  number  of  such  experi- 
ments, gives  the  following  as  the  average  digestion  coefficients 
obtained  in  all  recorded  experiments  up  to  1910. 

TABLE  173.  —  DIGESTIBILITY  BY  FOWLS 


% 

NUMBER 

OF 

EXPERI- 
MENTS 

ORGANIC 

MATTER 

CRUDE 
PROTEIN 

NITRO- 
GEN-FREE 
EXTRACT 

ETHER 
EXTRACT 

Bran  wheat 

-2 

% 
4.6  70 

% 
71  7O 

% 
46  oo 

% 
37  OO 

Beef  scrap      .         ... 

2 

80.20 

O2  60 

Qf    OO 

Beef  (lean  meat)      .... 
Barley 

2 

-2 

87.65 

77  17 

QO.2O 
77  32 

gcr  oo 

86.30 

67  86 

Buckwheat 

2 

60  38 

qn  4.0 

86  QO 

80  22 

Maize,  whole       
M^aize  cracked 

16 

2 

86.87 
87  30 

81.58 

72   2O 

91.32 

88  10 

88.11 
87  60 

Maize    
Clover 

2 

83.10 

27  7O 

74.60 

70  60 

86.00 

Id.  3O 

87.60 

0  Z     CQ 

India  wheat    

•7 

72  7O 

7  c  QO 

83  4.O 

83    80 

Millet    
Oats 

I  3 

62  60 

62.40 
71  31 

98.39 
OO  IO 

85.71 
87    80 

Peas      .     

•7 

77  O7 

87  oo 

84.  80 

80  01 

Wheat 

IO 

82  26 

7r  o? 

87  OA 

e-j  oO 

Rye  

2 

70  2O 

66  OO 

86  70 

22  60 

Potatoes    

6 

78.33 

46.94 

84.46 

Maine  Expt.  Sta.,  Bui.  184,  1910. 


RELATIVE  VALUES  OF  FEEDING  STUFFS      609 

Crude  fiber  appears  to  be  relatively  difficult  of  digestion  by 
fowls  and  the  results  obtained  upon  this  ingredient  were  vari- 
able and  apparently  capricious.  Aside  from  this,  a  comparison 
of  results  with  those  for  swine  shows  quite  a  close  general 
agreement  between  the  two  classes  of  animals. 

718.  Individuality.  —  In  addition  to  the  specific  differences 
just  considered,  differences  have  likewise  been  observed  in  the 
digestibility  of  the  same  feeding  stuff  by  individuals  of  the 
same  species.  To  some  extent  this  may  be  due  to  abnormal- 
ities, such  as  defective  teeth  or  chronic  diseases  of  the  digestive 
organs,  but  in  normal  animals  distinct  individual  differences 
also  seem  to  occur. 

In  their  compilation  of  the  results  of  American  digestion  ex- 
periments, Jordan  and  Hall x  were  unable  to  find  conclusive 
evidence  of  such  differences  in  digestive  power  and  are  inclined 
to  attribute  the  apparent  variations  which  were  observed  largely 
to  the  variability  at  different  times  already  considered  (712). 
The  experiments  by  G.  Kiihn,2  however,  which  were  cited  in 
the  discussion  of  the  latter  possibility,  seem  also  to  afford  in- 
dubitable instances  of  individual  differences  in*  cattle  and  the 
same  is  true  of  experiments  by  the  writer 3  in  which  three 
grade  Shorthorn  steers  were  under  observation  at  different  times 
for  five  years.  Carmichael,  Newlin  and  Grindley  4  have  like- 
wise observed  significant  differences  in  the  digestive  powers  of 
individual  pigs.  On  the  other  hand,  Christensen  and  Simpson  5 
made  three  series  of  digestion  trials  on  alfalfa  hay  for  two  suc- 
cessive years,  using  four  range  steers  each  year,  and  failed  to  find 
any  consistent  individual  differences. 

The  existence  of  time  variations  in  digestibility  (712)  renders 
it  somewhat  difficult  to  decide  whether  an  observed  difference 
in  the  digestion  of  the  same  feeding  stuff  by  two  animals  is  really 
an  expression  of  individuality  or  whether  it  is  in  a  sense  acci- 
dental. A  comparison  based  on  a  single  digestion  trial  as  or- 
dinarily made  is  liable  to  be  misleading,  and  to  secure  correct 
results  requires  either  a  number  of  trials  or  a  trial  extend- 
ing over  a  longer  period  than  is  ordinarily  employed.  On  the 

1  U.  S.  Dept.  Agr.,  Office  Expt.  Stas.,  Bui.  77  (1900),  88. 

2  Landw.  Vers.  Stat.,  29  (1883),  129,  147,  153. 
8  Penna.  Expt.  Sta.,  Bui.  42  (1898),  124. 

4  Science,  July  2,  1915,  p.  38.  5  New  Mexico  Expt.  Sta.,  Bui.  91  (1914). 

2  R 


6lO  NUTRITION  OF  FARM  ANIMALS 

whole,  however,  the  conclusion  seems  justified  that  animals  of 
the  same  species  may  differ  to  some  extent  in  their  digestive 
power  but  that  these  individual  differences  are  probably  less 
than  appear  to  be  indicated  by  the  results  of  single  digestion 
trials  and  are  certainly  much  too  small  to  account  in  any  degree 
for  the  economic  differences  in  animals.  Even  the  differences 
observed  in  the  results  of  short  digestion  trials  rarely  exceed 
three  or  four  per  cent  and  are  usually  materially  less  than  this. 

719.  Breed.  —  The  foregoing  facts  are  sufficient  of  them- 
selves to  render  improbable  the  existence  of  any  considerable 
breed  differences  as  regards  digestion,  and  this  conclusion  has 
been  confirmed  by  the  experiments  of  Haubner  and  Hofmeister,1 
of   Wolff 2   and   of  Armsby  and   Fries.3    The   recorded   data 
taken  together  fail  to  indicate  any  material  difference  in  the 
digestive  power  of  different  breeds  or  between  pure-bred  and 
scrub  animals. 

There  exists  a  somewhat  general  impression  that  animals 
which  show  themselves  superior  as  producers  of  meat,  milk, 
etc.,  whether  as  the  result  of  breed,  heredity,  or  of  individual 
variation,  owe  that  superiority,  in  part  at  least,  to  a  superior 
digestive  power ;  that  is,  it  is  supposed  that  the  improved  breeds 
of  farm  animals  and  the  superior  individual  animals  within  a 
breed  are  able  to  extract  more  nutriment  from  a  given  weight 
of  a  feed  than  can  inferior  animals.  The  reasons  for  the  un- 
doubted economic  superiority  of  some  individuals  over  others 
have  been  considered  in  previous  chapters.  So  far  as  differ- 
ences in  digestive  power  are  concerned,  however,  the  experimen- 
tal evidence  gives  little  support  to  the  popular  impression. 

720.  Age.  —  Comparisons   of    the    digestive   power   of    the 
same  animals  (lambs)  at  different  ages  were  made  by  Wolff 4 
in  1871-72  which  led  to  the  conclusion  that  between  the  ages  of 
six  and  fourteen  months  the  percentage  digestibility  of  the 
feed  remained  practically  unchanged  and    this  conclusion  is 
confirmed  by  the  results  of  an  experiment  by  Weiske5  under- 
taken primarily  for  another  purpose. 

721.  Work.  —  Investigations  on  the  effect  of  the  performance 
of  work  upon  the  digestibility  of  rations  have  naturally  been 

1  Landw.  Vers.  Stat.,  12  (1869),  8.  2  Landw.  Jahrb.,  1  (1872),  533. 

3  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  128. 

4  Landw.  Jahrb.,  2  (1873),  221.  5  Ibid.,  9  (1880),  205. 


RELATIVE  VALUES  OF  FEEDING  STUFFS  6ll 

made  upon  the  horse.  Experiments  upon  this  subject  have 
been  reported  by  Wolff  and  his  associates  at  Hohenheim  and  by 
Grandeau  and  LeClerc  at  Paris. 

Wolff's1  experiments  were  upon  a  single  animal,  a  draft  horse 
weighing  about  550  kgs.  (1200  pounds).  The  ration  remained 
the  same  in  all  the  periods  and  was  insufficient  to  maintain  the 
weight  of  the  animal  in  the  periods  of  heavier  work.  The 
work  was  that  of  draft,  done  at  a  slow  walk  (about  1.9  miles 
per  hour)  with  in  most  instances  a  draft  of  60  kgs.,  the  total  work 
per  day  (not  including  that  of  locomotion)  ranging  from  475,000 
to  1,800,000  kilogram  meters.  Under  these  conditions,  no 
effect  on  the  digestibility  of  the  mixed  rations  employed  was 
observed. 

Grandeau  and  LeClerc's  investigations2  were  made  upon 
several  different  horses  of  the  Paris  Cab  Company  and  in- 
cluded experiments  upon  work  and  others  upon  simple  loco- 
motion both  at  a  walk  and  a  trot  together  with  rest  ex- 
periments. 

The  plan  of  the  experiments  differed  from  that  of  Wolff's 
in  some  important  particulars.  The  animals  used  were  lighter 
(about  400  kgs.  as  compared  with  550  kgs.)  and  apparently  of 
a  more  active  temperament  as  indicated  by  their  more  rapid 
walk,  the  velocity  of  which  varied  from  2.6  to  3.0  miles  per 
hour.  The  work,  which  was  that  of  draft,  was  done  on  a  dyna- 
mometer similar  to  Wolff's.  The  draft  was  about  half  of  that 
of  Wolff's  experiments  and  the  total  amount  of  work3  was 
considerably  less,  ranging  in  most  cases  from  400,000  to  600,000 
kilogram  meters  per  day,  with  a  maximum  in  one  experiment  of 
785,000.  Its  amount  was  approximately  the  same  in  all  the 
experiments  in  each  series  and  was  not  greater  at  a  trot  than 
at  a  walk.4  Finally,  corresponding  to  the  main  purpose  of  the 
experiment,  which  was  to  study  the  feed  requirements  of  cab 
horses,  the  rations  in  the  periods  of  work  or  of  walking  exercise 
were  heavier  than  in  those  in  the  periods  of  rest,  the  increase 
being  one-tenth  in  the  experiments  on  locomotion  and,  in  most 
cases,  one-half  in  the  experiments  on  work.  The  proportions 

JLandw.  Jahrb.,  8,  Ergzbd.  I   (1879),  73;  16,  Ergzbd.  Ill  (1887),  53-71. 
2 L'alimentation  du  cheval  de  trait;  Berger-Levrault  et  cie,  1882-89. 

3  Not  including  that  of  locomotion. 

4  The  total  work  in  the  former  case  was,  of  course,  somewhat  greater  on  account 
of  the  greater  expenditure  of  energy  in  trotting  as  compared  with  walking  (664). 


6l2  NUTRITION  OF  FARM  ANIMALS      * 

of  the  different  feeding  stuffs  in  the  rations,  however,  remained 
the  same,  except  in  a  very  few  cases. 

On  the  whole,  and  despite  some  irregularities  in  the  results 
on  single  ingredients,  Grandeau  and  LeClerc's  results  agree 
with  Wolff's  in  showing  that  work  even  at  a  somewhat  rapid 
walk  does  not  materially  affect  the  digestibility  of  rations.  On 
the  other  hand,  they  show  a  distinct  decrease  of  the  percentage 
digestibility  in  the  periods  in  which  the  work  was  done  at  a 
trot.  It  scarcely  seems  that  this  effect  can  be  ascribed  to  the 
work  as  such,  since  the  measured  amount  was  less  than  in  Wolff's 
experiments  and  was  not  greater  at  a  trot  than  at  a  walk.  More- 
over, mere  horizontal  locomotion  at  a  trot,  in  some  instances  at 
least,  seems  to  have  produced  the  same  effect,  which  apparently 
is  due  to  the  difference  in  gait.  It  is  true  that  the  rations  were 
heavier  in  the  work  periods  and  that  this  (722)  may  possibly 
have  affected  the  digestibility,  but  no  reason  is  apparent  why 
it  should  have  produced  a  greater  effect  in  the  trotting  periods 
than  in  the  walking  periods. 

The  influence  of  work  has  also  been  investigated  in  a  different  way 
by  Tangl 1  and  by  Scheunert.2  A  weighed  amount  of  oats  was  fed 
after  36  hours  of  fasting  and  the  animal  was  killed  from  one  to  five 
hours  later  and  the  contents  of  the  stomach  and  small  intestines 
weighed  and  analyzed.  On  the  assumption  that  none  of  the  crude 
fiber  of  the  oats  was  digested  in  this  portion  of  the  alimentary  tract, 
the  results  show  that  work  delays  the  passage  of  the  feed  from  the 
stomach  to  the  intestines,  especially  during  the  first  one  or  two  hours. 
As  a  consequence,  the  gastric  juice  penetrates  the  larger  mass  of  the 
feed  more  slowly  and  more  of  it  is  neutralized  by  the  saliva,  so  that 
the  stage  of  starch  digestion  is  prolonged  and  that  of  protein  diges- 
tion shortened,  the  result  being  that  more  carbohydrates  and  less  pro- 
tein are  digested.  In  the  later  stages  of  digestion  the  differences  tend 
to  equalize  themselves,  while  the  effect  of  work  upon  the  intestinal 
digestion  was  found  to  be  small.  Scheunert  computes  that  the  total 
digestibility  was  considerably  increased  by  the  performance  of  work. 
As  noted,  however,  the  results  cover  only  the  first  five  or  six  hours 
of  digestion.  The  method  of  comparison  is  confessedly  an  approxi- 
mate one  and  the  results  show  very  considerable  variations  among 
themselves.  Only  actual  digestion  experiments  suffice  to  decide  the 
question  of  the  total  effect  of  work  upon  digestion. 

1  Arch.  Physiol.  (Pfliiger) ;  65  (1896),  545. 

2  Arch.  Physiol.  (Pfliiger) ;  109  (1905),  145  J  Landw.  Jahrb.,  34  (1905),  805. 


RELATIVE  VALUES  OF  FEEDING  STUFFS  613 


Conditions  relating  to  the  feed 

722.  Quantity  of  feed.  —  Current  methods  of  computing 
rations  regard  the  digestibility  of  feeding  stuffs  as  unaffected 
by  the  amounts  consumed.  As  regards  exclusive  feeding 
with  roughage,  the  results  of  a  considerable  number  of  ex- 
periments by  various  investigators  appear  to  justify  this  view. 
With  mixed  rations  of  roughage  and  concentrates  fewer  ex- 
periments have  been  made,  but  the  results  indicate  a  distinct 
decrease  in  the  percentage  digestibility  when  the  amount  of 
the  ration  is  increased  considerably  above  that  required  for 
maintenance. 

Roughage.  —  The  early  experiments  of  Henneberg  and  Stohmann  on 
cattle  include  several  cases  in  which  varying  amounts  of  clover  and 
meadow  hay  were  fed  and  in  which  the  digestibility  was  substantially 
unaffected  by  the  quantity  consumed,  and  the  same  was  found  to  be 
true  by  Wolff  at  Hohenheim  in  a  number  of  experiments  on  sheep.1 
Later  comparative  experiments  by  the  same  investigator  2  on  sheep 
and  horses  have  confirmed  his  earlier  results,  as  have  also  those  of 
Tangl  and  Weiser 3  upon  sheep  fed  alfalfa  hay  or  alfalfa  silage,  while 
Miintz  and  Girard 4  likewise  found  no  distinct  effect  of  the  quantity 
consumed  upon  the  digestibility  of  alfalfa  hay  by  the  horse.  In 
three  experiments  by  Armsby  and  Fries 6  on  each  of  two  steers  a  sub- 
maintenance  ration  of  timothy  hay  was  slightly  better  digested  than 
a  maintenance  ration  in  five  cases  out  of  six,  but  the  differences  were 
small,  amounting  to  from  i.o  to  2.7  per  cent  on  the  dry  matter. 
Later  unpublished  experiments  have  given  similar  results.  In  earlier 
experiments  6  by  the  same  authors  on  different  amounts  of  clover  hay, 
practically  no  differences  were  observed.  . 

Mixed  rations.  —  Kellner 7  obtained  the  following  results  in  four 
periods  in  which  varying  amounts  of  a  mixed  ration  consisting  of 
meadow  hay,  dried  molasses  beet  pulp,  rye  bran  and  cottonseed  meal 
were  fed  to  cattle. 

1  Compare  Wolff,  Die  Ernahrung  der  landwirtschaftlichen  Nutztiere,  pp.  63 
and  64. 

2Landw.  Jahrb.,  1  (1872),  533;  Landw.  Vers.  Stat.,  21  (1878),  19. 

3  Landw.  Vers.  Stat.,  74  (1911),  277  and  282. 

4  Centbl.  Agr.  Chem.,  27  (1898),  756. 

5U.  S.  Dept.  of  Agri.,  Bur.  Anim.  Indus.,  Bui.  128  (1911),  p.  27. 
6U.  S.  Dept.  of  Agri.,  Bur.  Anim.  Indus.,  Bui.  74  (1905),  pp.  12-13;    Bui.  No. 
101  (1908),  pp.  11-13. 

7  Ernahrung  landw.  Nutztiere,  6th  Ed.,  p.  49. 


614 


NUTRITION  OF  FARM  ANIMALS 


TABLE  174.  —  EFFECT  OF  AMOUNT  OF  MIXED   RATION   CONSUMED   ON 
DIGESTIBILITY 


DIGESTIBILITY 

DAILY 
RATION 

Organic 
Matter 

Crude 
Protein 

Crude 
Fiber 

Nitrogen- 
free 
Extract 

Ether 
Extract 

Kgs. 

% 

% 

% 

% 

% 

Period  I    .... 

10.84 

76.1 

71.0 

62.8 

82.0 

63.5 

Period  II  .... 

13.01 

74-7 

68.3 

6l.2 

80.8 

64.4 

Period  III      ... 

15.18 

72.8 

65-8 

59-2 

7Q.O 

64.2 

Period  IV      .     .     . 

10.84 

75-8 

71.2 

62.6 

8l.2 

67.6 

Eckles  1  determined  the  digestibility  of  mixed  rations  sufficient 
for  maximum  milk  production,  and  thirteen  months  later,  when  the 
cows  were  dry,  that  of  a  maintenance  ration  of  the  same  mixture  of 
feeding  stuffs.  About  thirty  per  cent  of  the  dry  matter  of  the  ration 
was  derived  from  hay,  thirty-six  per  cent  from  silage  and  thirty-four 
per  cent  from  grain. 

TABLE  175.  —  DIGESTIBILITY  OF  MIXED  RATIONS  BY  Cows 


DRY 

PERCENTAGE  DIGESTIBILITY 

MIXED 

MATTER 

RATION 

PER 

HEAD 

PER 
1000 

LIVE 
WEIGHT  2 

Organic 
Matter 

Crude 
Protein 

Crude 
Fiber 

Nitro- 
gen-free 
Extract 

Ether 
Ex- 
tract 

Cow  No.  27 

Kgs. 

Full  ration     .... 

24-95 

3L30 

66.3 

58.8 

53-8 

72.6 

67.0 

Maintenance  ration    . 

8.71 

10.95 

73-8 

67.3 

55-3 

82.1 

73-2 

Cow  No.  62 

Full  ration     .... 

15-88 

19.88 

67.0 

60.6 

53-9 

73-6 

59-8 

Maintenance  ration     . 

7.62 

9.58 

72.2 

65.5 

52.1 

81.0 

73-9 

Mumford,  Grindley,  Hall  and  Emmett 3  determined  the  digestibil- 
ity of  four  different  mixed  rations  of  hay  and  grain  by  four  pairs  of 
cattle  receiving  respectively  slightly  more  than  a  maintenance  ration, 
one-third  feed,  two- thirds  feed  and  full  feed.  One  animal  of  the  full- 
fed  pair  showed  a  distinctly  lower  digestive  power  than  the  other  in 
all  the  periods  and  the  same  was  true  of  one  animal  receiving  the 
two-thirds  feed  in  the  last  two  periods.  The  results  upon  the  other 
animal  in  this  case  are  shown  in  the  table  in  parenthesis :  — 


Mo.  Expt.  Sta.,  Research  Bui.  4. 


2  Approximate. 


3  Ills.  Expt.  Sta.,  Bui.  172  (1914). 


RELATIVE  VALUES  OF  FEEDING  STUFFS  615 

TABLE  176.  —  DIGESTIBILITY  OF  DRY  MATTER  BY  CATTLE 


PERIOD  i 

PERIOD  2 

PERIOD  3 

PERIOD  4 

AVERAGE 

Ratio    of    hay    to 
grain     .... 

i  :  i 

1:3 

i:  5 

i:  5 

Per  Cent 

Per  Cent 

Per  Cent 

Per  Cent 

Per  Cent 

Maintenance     .     . 
One-third  feed 
Two-thirds  feed      . 
Full  feed  .... 

69.9 
67.12 
65.62 
63.03  (64.50) 

77.28 
72.06 
69.07 
64.56  (69.64) 

78.79 
75-74 
73-62  (75-57) 
70.11  (74.81) 

79-99 
77-14 
75.10  (77-80) 
76.12  (79-53) 

76.51 
73-02 
70.83  (72.02) 
68.46  (72.12) 

In  these  experiments  the  digestibility  of  the  maintenance  ration 
appears  to  have  been  distinctly  higher  than  that  of  the  heavier  rations 
in  Period  i,  in  which  the  largest  proportion  of  hay  was  fed.  The 
differences  became  much  less  marked  as  the  total  feed  was  progres- 
sively increased,  and  as  between  the  two-thirds  and  full-feed  ration 
was  scarcely  significant,  especially  in  view  of  the  individual  differ- 
ences in  this  pair.  The  effect  also  decreased  as  the  proportion  of 
grain  in  the  ration  was  increased,  so  that  on  the  average  of  the  four 
periods  but  little  difference  is  shown  with  certainty  among  the  three 
heavier  rations. 

Unpublished  experiments  by  Armsby  and  Fries,  in  which  varying 
amounts  of  a  uniform  mixture  of  two-thirds  grain  and  one-third  hay 
were  fed  to  steers,  afford  confirmation  of  the  foregoing  results :  — 

TABLE  177.  —  DIGESTIBILITY  OF  MIXED  RATIONS  BY  STEERS 


DRY 

PERCENTAGE  DIGESTIBILITY 

AMOUNT 

MATTER 

OF 

MIXED 
RATION 

PER 
1000 

LIVE 
WT. 

Organic 
Matter 

Crude 
Protein 

Crude 
Fiber 

Nitro- 
gen-free 
Extract 

Ether 
Extract 

Steer  C 

Kgs. 

Period  2     .... 

2-55 

8.26 

68.8 

67.2 

25.2 

79-2 

75-7 

Period  3     .... 

i.  80 

5.83 

74-9 

73-7 

39-5 

83.4 

78.9 

Steer  E 

Period  i     .... 

3-75 

15-74 

68.9 

66.9 

40.6 

76.3 

70.6 

Period  2     .... 

2.04 

8.58 

75-1 

65-2 

49-9 

83-0 

78.0 

Period  3     .... 

1-45 

5-64 

74.1 

68.1 

44-7 

82.4 

78.4 

Steer  F 

Period  i     .     .     .     . 

5-4 

I5-2S 

68.4 

65.0 

35-6 

76.7 

77-6 

Period  2     .... 

3-2 

9.36 

72.1 

66.9 

37-o 

81.1 

80.6 

Period  3     .... 

1.9 

5-59 

74-2 

70.2 

40.4 

82.7 

80.0 

6i6 


NUTRITION  OF  FARM  ANIMALS 


One  would  naturally  be  inclined  to  ascribe  the  lower  diges- 
tibility of  heavier  rations  to  their  greater  bulk  and  relatively 
more  rapid  passage  through  the  digestive  tract,  and  in  part  to 
the  consequent  lessened  extent  of  the  bacterial  fermenta- 
tions. It  would  seem  that  on  liberal  rations  material  poten- 
tially digestible  and  resorbable  may  thus  escape  digestion  and 
appear  in  the  feces.  Some  of  the  reasons  for  this  have  al- 
ready been  indicated  in  discussing  the  feces  as  a  feed  residue 
(155).  The  presence  of  considerable  amounts  of  undigested 
grains  or  fragments  of  grain  in  the  feces  of  heavily  fed  animals 
is  readily  demonstrated  by  washing  out  the  finer  portions,  but 
actual  digestion  experiments  to  determine  the  extent  of  this 
loss  have  not  yet  been  reported. 

723.  Excess  of  carbohydrates.  —  It  has  been  established  by 
numerous  experiments  that  an  undue  proportion  of  carbohy- 
drates in  a  ration  tends  to  reduce  its  digestibility,  especially  by 
ruminants.  The  effect  is  most  distinct  when  pure  digestible  car- 
bohydrates are  added  to  a  ration,  but  is  manifest  also  when  large 
amounts  of  feeding  stuffs  rich  in  carbohydrates  are  introduced. 

An  example  of  the  former  is  afforded  by  an  experiment  by 
G.  Kiihn  1  on  two  oxen.  It  was  divided  into  three  periods,  in 
the  first  of  which  the  animals  received  a  daily  ration  of  9  kgs. 
of  hay  to  which,  in  the  second  and  third  periods,  2  kgs.  and  3. 5 
kgs.  of  starch,  respectively,  were  added.  Assuming  the  starch 
to  have  been  completely  digested  2  the  following  amounts  of 
the  several  ingredients  were  computed  to  have  been  digested 
from  the  hay  by  Ox  V. 

TABLE  178.  —  NUTRIENTS  DIGESTED  FROM  HAY,  WITH  AND  WITHOUT 

STARCH 


PERIOD 

DRY 

MATTER 

ORGANIC 
MATTER 

CRUDE 
PRO- 
TEIN 

CRUDE 
FIBER 

NITRO- 
GEN- 
FREE 
EXTRACT 

ETHER 
EX- 
TRACT 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

I       ... 

No  starch 

4549 

4378 

451 

1572 

2315 

40 

II     ... 

2  kgs.  of  starch 

43*7 

4161 

407 

1475 

2239 

41 

Ill   ... 

3.5  kgs.  of  starch 

3QI4 

3746 

3OI 

1392 

20l6 

38 

1  Landw.  Vers.  Stat.,  44  (1894),  470-472. 

2  No  starch  could  be  detected  microscopically  in  the  feces. 


RELATIVE   VALUES  OF   FEEDING   STUFFS 


6I7 


'  Expressed  in  another  way,  the  feces  in  Periods  II  and  III 
contained  the  following  amounts  of  hay  ingredients  which,  ac- 
cording to  the  results  of  Period  I,  must  be  regarded  as  digestible, 
but  which  under  the  influence  of  the  addition  of  starch  escaped 
digestion. 

TABLE  179.  —  DIGESTIBLE  NUTRIENTS  OF  HAY  ESCAPING  IN  FECES 


PERIOD 

DRY 

MATTER 

ORGANIC 
MATTER 

CRUDE 
PRO- 
TEIN 

CRUDE 
FIBER 

NITRO- 
GEN- 
FREE 
EXTRACT 

ETHER 
EX- 
TRACT 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

II     ... 

2  Kgs.  starch 

232 

217 

44 

97 

76 

-  i 

Ill   ... 

3.5  Kgs.  starch 

635 

632 

150 

1  80 

299 

2 

The  foregoing  is  a  typical  example  of  the  results  of  numerous 
similar  experiments  on  ruminants  in  which  starch,  sugar,  pectin 
substances  and  even  cellulose  have  been  added  to  hay  and  to 
mixed  rations.  Other  things  being  equal,  the  magnitude  of  the 
effect  has  usually  increased,  as  in  this  instance,  with  the  quan- 
tity of  carbohydrates  added.  Its  total  amount  has  varied  con- 
siderably in  different  experiments,  but  qualitatively  the  result 
has  been  uniformly  the  same.  This  constitutes  the  so-called 
"  depression  of  digestibility,"  since,  of  course,  the  digestion 
coefficients  are  lowered  by  the  escape  of  potentially  digestible 
matter  in  the  feces.  It  should  be  noted,  however,  that  in  some 
of  these  instances  more  or  less  of  the  added  carbohydrate  (starch) 
has  itself  escaped  digestion.  According  to  experiments  by 
Wolff,1  swine  appear  to  be  much  less  sensitive  to  this  influence 
of  carbohydrates  than  are  ruminants  and  a  few  observations 
by  Grandeau  and  Alekan  2  seem  to  indicate  that  the  same 
may  be  true  of  the  horse. 

724.  Feeding  stuffs  rich  in  carbohydrates,  as  well  as  such  ma- 
terials as  starch  or  sugar,  may  apparently  likewise  cause  a  de- 
crease of  digestibility,  although  the  quantitative  relations  can- 
not always  be  so  clearly  followed  as  in  experiments  with  pure 
carbohydrates.  Thus  six  experiments  with  beet  molasses  by 

1  Landw.  Vers.  Stat.,  19  (1876),  273. 

2  Jahresber.  Agr.  Chem.,  49  (1906),  350;   Ann.  Sci.  Agron.,  1904,  I,  30,  330. 


6i8 


NUTRITION  OF  FARM  ANIMALS 


Lehmann  1  and  one  by  Kellner  2  showed  that  this  substance, 
like  the  pure  carbohydrates,  caused  a  depression  in  the  di- 
gestibility of  all  the  ingredients  of  a  basal  ration,  but  in  two 
later  trials  by  Kellner  3  the  only  effect  was  on  the  digestibility 
of  the  crude  fiber. 

The  question  has  been  especially  investigated,  however,  by 
Wolff  in  regard  to  the  feeding  of  tubers  and  roots.  Heavy  feed- 
ing of  these  materials  is  generally  stated,  on  the  strength  of  his 
experiments,  to  result  in  a  pronounced  decrease  in  the  diges- 
tibility of  the  remainder  of  the  ration,  although,  as  Wolff  him- 
self points  out,  the  evidence  is  by  no  means  conclusive. 

In  Wolff's  extensive  series  of  experiments  on  sheep  4  increasing 
quantities  of  roots  or  potatoes  were  fed  along  with  hay  whose  diges- 
tibility had  been  previously  determined,  and  it  was  found  that  as  the 
amount  of  roots  added  to  the  ration  was  increased,  the  feces  contained 
increasing  amounts  of  undigested  nutrients.  For  example,  in  one 
experiment  with  meadow  hay  and  sugar  beets,  the  percentage  digesti- 
bility of  the  hay,  computed  on  the  assumption  that  the  sugar  beets 
were  completely  digestible,  was  as  follows :  — 

TABLE  180.  —  COMPUTED  PERCENTAGE  DIGESTIBILITY  OF  HAY  WITH  AND 
WITHOUT  SUGAR  BEETS 


DRY 

MATTER 

ORGANIC 
MATTER 

CRUDE 
PROTEIN 

CRJJDE 
FIBER 

NITRO- 
GEN-FREE 
EXTRACT 

ETHER 
EXTRACT 

Fed  alone       .     .     . 
Fed  with  sugar  beets 

55-9 
43-9 

59-2 
50.0 

57-6 
51.0 

55-2 

62.1 
50.0 

60.0 
29.4 

What  seems  a  more  reasonable  method  of  comparison,  however, 
is  to  compute  the  digestibility  of  the  roots  in  the  first  instance  on 
the  assumption  of  unaltered  digestibility  of  the  hay,  just  as  in  the 
case  of  concentrates  (161)  and  to  see  whether  the  coefficients  thus  ob- 
tained show  any  decrease  as  the  proportion  of  roots  fed  is  increased. 
Wolff  has  carried  out  the  computation  in  this  manner  for  his  entire 
series  of  experiments,  numbering  in  all  no  single  trials.  The  aver- 

1  Landw.  Jahrb.,  25  Erzgbd.  II  (1896),  117. 

2  Landw.  Vers.  Stat.,  53  (1900),  199. 
3Ernahrung  landw.  Nutztiere,  5th  Ed.,  pp.  158-175. 
4  Landw.  Jahrb.,  8  Ergzbd.  I  (1879),  123. 


RELATIVE  VALUES  OF  FEEDING  STUFFS  619 

age  results  for  total  organic  matter  and  for  nitrogen-free  extract  are 
fairly  uniform  in  each  series  of  experiments,  although  there  was  some- 
what more  variation  in  the  individual  trials,  and  fail  to  give  any 
decided  indication  of  a  diminished  digestibility  with  the  increasing 
amounts  of  roots  consumed.  The  computed  digestibility  of  the  crude 
protein  is  more  or  less  variable,  but  on  the  whole  a  decreased  diges- 
tibility of  this  ingredient  as  the  proportion  of  roots  to  hay  increased 
seems  to  be  plainly  shown. 

It  is,  of  course,  impossible  to  determine  in  a  digestion  experi- 
ment in  which  roots  are  added  to  a  basal  ration  what  propor- 
tion of  the  fecal  matter  is  derived  from  the  roots  and  what  from 
the  remaining  ingredients,  and  such  results  as  those  of  Wolff 
may  be  interpreted  either  as  showing  a  fairly  constant  diges- 
tibility of  both  the  hay  and  the  roots  (aside  from  crude  protein), 
or,  on  the  assumption  of  complete  digestibility  of  the  roots,  as 
showing  a  progressive  depression  in  the  digestibility  of  the 
hay.  To  the  writer,  the  former  appears  on  the  whole  the  more 
reasonable  course,  although  it  should  be  added  that  in  some  of 
the  experiments  the  absolute  amount  of  crude  fiber  in  the  feces 
was  increased  by  an  amount  greater  than  that  contained  in  the 
roots  consumed,  thus  demonstrating  a  depression  of  the  diges- 
tibility of  this  constituent  of  the  hay.  Probably  the  truth 
lies  between  the  two  views.  It  is  unlikely  that  roots  are  en- 
tirely digestible  and,  on  the  other  hand,  it  is  probable  that  a 
large  proportion  of  them  may  diminish  to  some  extent  the  di- 
gestibility of  other  feeding  stuffs  consumed  with  them.  It  is 
to  be  remembered,  however,  that  roots  contain  not  altogether 
inconsiderable  quantities  of  crude  protein  which,  as  shown  in  a 
following  paragraph  (727),  tends  to  offset  the  effects  of  their 
carbohydrates. 

725.  Cause  of  diminished  digestibility  of  protein.  —  Atten- 
tion has  already  been  called  (163-167)  to  the  influence  of  the 
excretory  products  contained  in  the  feces  on  the  apparent  diges- 
tibility of  the  nutrients  and  especially  of  protein.  According 
to  Kellner's  and  Pfeiffer's  results,  the  digestion  of  each  100 
grams  of  dry  matter,  whether  protein  or  nitrogen-free  material, 
results  in  the  excretion  in  the  feces  of  approximately  0.4  gram 
of  nitrogen  in  the  form  of  these  excretory  products.  If,  then, 
a  kilogram  of  dry  starch  be  added  to  a  basal  ration,  the  nitrog- 
enous excretory  products  in  the  feces  are  increased  by  ap- 


620  NyTRITION  OF  FARM  ANIMALS 

proximately  25  grams,  so  that  apparently  25  grams  less  of  pro- 
tein is  digested  from  the  basal  ration,  while  in  reality  the  true 
digestion  may  not  have  been  affected.  Thus  in  Kiihn's  exper- 
iment with  hay  and  starch  (723)  the  nitrogenous  excretory 
products  corresponding  to  the  1646  grams  dry  matter  of  the 
2  kgs.  of  starch  consumed,  would  be  approximately  40  grams, 
while  the  excess  actually  found  was  44  grams,  the  difference 
being  insignificant. 

The  agreement  is  by  no  means  always  so  close  as  in  this 
instance  and  in  none  of  the  experiments  on  the  addition  of  car- 
bohydrates which  have  been  cited  was  the  true  digestibility 
(166)  of  the  protein  determined.  Nevertheless,  the  general 
conclusion  seems  justified  that  at  least  the  larger  part  of  the 
influence  of  carbohydrates  and  of  feeding  stuffs  rich  in  car- 
bohydrates on  the  apparent  digestibility  of  the  protein  of  the 
feed  is  due  to  the  fact  that,  when  added  to  a  basal  ration,  they 
increase  the  nitrogenous  excretory  products  in  the  feces.  On 
the  other  hand,  however,  it  must  be  remembered,  that  while 
the  true  digestibility  may  not  be  lowered,  it  is,  as  already 
pointed  out  (167),  the  apparent  digestibility  which  measures 
the  real  advantage  derived  by  the  animal  from  the  digestion 
of  its  feed.  Whether  the  increased  excretion  of  nitrogenous 
matter  in  the  feces  after  carbohydrate  feeding  be  due  to  an 
apparent  or  a  real  depression  of  digestibility,  or  to  both  com- 
bined, it  is  none  the  less  a  loss  of  protein  from  the  body. 

In  general  the  depression  in  the  percentage  digestibility  of 
the  protein  is  greater  the  poorer  the  basal  ration  is  in  this  in- 
gredient. As  Kellner x  has  pointed  out,  however,  this  does 
not  justify  the  statement  frequently  made  that  the  magnitude 
of  the  depression  is  dependent  upon  the  nutritive  ratio  of  the 
feed.  The  difference  is  purely  a  mathematical  one.  A  de- 
crease of  the  digestibility  of  the  protein  by  50  grams,  for  ex- 
ample, is  relatively  very  much  greater  in  a  basal  ration  of  oat 
straw,  containing  only  140  grams  of  apparently  digestible  crude 
protein  than  in  a  basal  ration  of  meadow  hay  containing  430 
grams  of  digestible  protein. 

The  fact  that  the  addition  of  protein  tends  to  decrease  the 
apparent  digestibility  of  the  protein  of  a  basal  ration  is  also 
readily  explicable  from  this  point  of  view.  Pfeiffer's  exper- 

1  Landw.  Vers.  Stat.,  44  (1894),  344. 


RELATIVE  VALUES  OF  FEEDING  STUFFS     621 

iments  (162)  showed  that  the  increase  in  the  nitrogenous  ex- 
cretory products  in  the  feces  was  about  the  same  whether  the 
added  digestible  matter  consisted  of  carbohydrates  or  of  protein. 
Consequently,  the  addition  of  protein  to  a  ration  would  tend 
to  diminish  the  apparent  digestibility  of  the  protein  just  as 
would  the  addition  of  carbohydrates. 

The  non-proteins,  especially  when  given  in  the  form  of  green 
vegetable  material  and  roots,  likewise  increase  the  nitrogen  con- 
tent of  the  feces,  but  a  review  of  the  literature  of  the  subject l 
shows  that,  as  in  the  case  of  the  proteins,  the  increase  consists, 
at  least  in  large  part,  of  metabolic  products  and  does  not  indicate 
any  decrease  in  the  true  digestibility  of  the  protein,  although 
it  does,  of  course,  decrease  the  amount  available  to  the  organism. 

726.  Cause  of  diminished  digestibility  of  carbohydrates.  — 
The  depression  of  digestibility  of  the  non-nitrogenous  ingredi- 
ents of  the  feed  of  ruminants  appears  to  be  due  to  an  entirely 
different  cause,  viz.,  to  a  modification  in  the  fermentation  pro- 
cesses in  the  rumen,  and  the  fact  that  these  effects  are  observed 
chiefly  on  this  class  of  animals  lends  strong  support  to  this  view. 

It  has  already  been  stated  (128-132)  that  the  disappearance 
of  more  or  less  of  the  comparatively  insoluble  carbohydrates  of 
the  feed  during  its  passage  through  the  alimentary  tract  is  due, 
particularly  in  ruminants,  to  a  bacterial  fermentation,  occur- 
ring principally  in  the  first  stomach  and  yielding  chiefly  carbon 
dioxid,  methane  and  organic  acids.  Furthermore,  it  has  been 
shown  that  when  the  more  soluble  carbohydrates,  like  starch 
and  sugar,  are  introduced  into  the  ration  they  are  attacked  by 
the  organisms  and  undergo  the  same  fermentation,  yielding  cor- 
responding amounts  of  the  characteristic  gaseous  product, 
methane.  It  can  scarcely  be  doubted  that  the  decreased  di- 
gestibility of  the  less  soluble  carbohydrates  under  these  cir- 
cumstances is  due  to  a  partial  diversion  of  the  activity  of  the 
ferment  organisms  to  the  maltose  resulting  from  the  action  of 
the  saliva  on  the  starch  or  to  the  sugar  directly  added,  since 
these  substances  are  presumably  more  readily  attacked  than 
cellulose  and  the  like. 

The  action  of  nitrogenous  substances  in  counteracting  this 
effect  of  an  excess  of  readily  soluble  carbohydrates  is  plausi- 
bly explained  as  due  to  its  supplying  more  nitrogenous  food 

1  Compare  U.  S.  Dept.  of  Agr.,  Bur.  Anim.  Indus.,  Bui.  139. 


622  NUTRITION  OF   FARM  ANIMALS 

for  the  organisms  and  so  stimulating  their  multiplication  and 
activity,  and  the  fact  that  readily  soluble  nitrogenous  materials 
like  amino  acids  or  ammonium  salts  seem  to  be  particularly 
effective  is  quite  in  harmony  with  this  view.  The  action  of 
nitrogenous  materials  in  stopping  the  excretion  of  undigested 
starch,  on  this  view,  would  be  explained  as  due  to  an  increase 
.of  the  proportion  fermented,  leaving  less  to  be  acted  on  by  the 
digestive  juices  of  the  intestines. 

727.  Effect  of  addition  of  protein.  —  It  was  shown  in  the 
last  paragraph  that  rations  containing  a  large  portion  of  car- 
bohydrates and  therefore  relatively  deficient  in  protein,  i.e., 
those  having  a  wide  nutritive  ratio,  are  likely  to  show  an  im- 
paired digestibility,  especially  by  ruminants.     Correcting  this 
condition  by  increasing  the  protein  content  of  such  rations  tends, 
as  would  be  expected,  to  increase  their  digestibility. 

Trials  have  been  macle  by  several  investigators  of  the  effect  of 
the  addition  of  nearly  pure  protein  (wheat  gluten  with  78  per 
cent  of  crude  protein,  or  fish  meal  with  96  per  cent  of  crude 
protein  in  the  organic  matter)  to  a  basal  ration.  In  general, 
such  an  addition  has  had  little  effect  on  the  digestibility  of  the 
protein  of  the  basal  ration,  but  in  several  experiments  on  rumi- 
nants an  increased  digestibility  of  crude  fiber,  and,  in  some  cases 
of  the  nitrogen-free  extract,  has  been  observed,  especially,  with 
basal  rations  poor  in  protein.  In  other  instances,  however, 
particularly  when  the  deficiency  in  protein  was  less  marked, 
this  effect  has  been  either  slight  or  entirely  absent  and  the 
same  is  true  of  such  experiments  on  swine  as  have  been  thus 
far  reported.  Experiments  are  also  on  record  in  which  the 
addition  of  feeding  stuffs  rich  in  protein,  such  as  oil  cake  or 
legumes,  has  distinctly  increased  the  digestibility  of  the  crude 
fiber  of  a  basal  ration  and  others  in  which  such  an  addition 
has  stopped  an  excretion  of  undigested  starch  in  the  feces. 

728.  Effect  of  non-protein.  —  The  addition  to  the  basal  ra- 
tion of  ruminants  of  digestible  non-protein  in  the  form  of  plant 
extracts  as  a  rule  tends  to  diminish  the  apparent  digestibility 
of  the  protein  of  the  basal  ration,  i.e.,  to  increase  the  excretion 
of  nitrogen  in  the  feces,  while  the  simpler  forms  of  non-protein, 
such  as  asparagin  or  ammonium  salts,  have  not  usually  pro- 
duced this  effect.1 

1  Compare  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  139  (1911),  pp.  14-28. 


RELATIVE  VALUES  OF  FEEDING  STUFFS 


623 


On  the  other  hand,  the  effect  of  protein  in  increasing  the  di- 
gestibility of  the  non-nitrogenous  ingredients  of  rations  contain- 
ing an  excess  of  carbohydrates  is  shared  also  by  the  non-pro- 
teins, such  comparatively  simple  substances  as  asparagin  or 
even  ammonium  salts  having  in  a  number  of  instances  exerted 
a  marked  influence  of  this  sort. 

729.  Influence  of  drying.  —  The  simple  removal  of  water 
from  a  feeding  stuff  affects  its  digestibility  but  slightly.  Weiske l 
compared  the  digestibility  of  green  and  dried  alfalfa  and  espar- 
cet  by  sheep.  In  these  experiments  the  forage  was  mowed 
daily,  one-half  of  it  fed  and  the  other  half  dried  without  loss, 
which  was  a  comparatively  easy  task  with  the  relatively  small 
amounts  to  be  handled.  In  the  second  half  of  the  experiment 
the  portions  of  dried  forage  were  fed  to  the  same  animals  in  the 


TABLE  181.  —  PERCENTAGE  DIGESTIBILITY  OF  FORAGE,  GREEN  AND  DRIED 


TOTAL 
ORGANIC 

MATTER 

CRUDE 
PROTEIN 

CRUDE 
FIBER 

NITRO- 
GEN-FREE 
EXTRACT 

ETHER 
EXTRACT 

ASH 

WEISKE 

Alfalfa 

Green    .... 

67.40 

83.08 

45-15 

72.79 

51.46 

Dried     .... 

66.69 

82.73 

44.83 

71.71 

5L30 

Difference   .     . 

-0.71 

-  0.35 

-  0.32 

-  1.  08 

—    0.16 

Esparcet 

Green    .... 

66.35 

72.50 

42.16 

78.29 

66.68 

50.21 

Dried     .... 

62.12 

69.98 

36.40 

74-35 

66.24 

45-59 

Difference   .     . 

-  4.23 

-  2.52 

-5.76 

-  3-94 

-  0.44 

—    4.62 

ARMSBY  AND 

CALDWELL 

Grass 

Green    .... 

68.87 

65.66 

74-37 

73-iS 

54-73 

50-05 

Dried     .... 

7I.3I 

71.66 

76.78 

72-95 

60.06 

55.56 

Difference   .     . 

+  2.44 

+  6.00 

+  2.41 

-0.23 

+  5-33 

+  5.5i 

MORGEN 

Grass 

Green    .... 

66.4  2 

69.6 

65.6 

77-8 

65.6 

30.7 

Dried     .... 

63.4  2 

55-7 

66.3 

73-8 

66.3 

12.5 

Difference   .     . 

-  3-o2 

-  3-9 

+  0.7 

-  4.0 

+  0.7 

-  18.2 

1  Jour.  f.  Landw.,  25  (1877),  170. 

2  Total  dry  matter. 


624 


NUTRITION  OF   FARM   ANIMALS 


same  order  that  the  green  forage  was.  Armsby  and  Caldwell l 
subsequently  made  a  similar  experiment  upon  a  cow  by  sub- 
stantially the  same  plan,  using  mixed  grasses  cut  while  still 
young  and  corresponding  substantially  to  pasture  grass,  and 
Morgen  z  has  reported  comparisons  of  the  same  sort  on  three 
sheep.  The  average  results  of  the  four  comparisons  are  shown 
in  Table  181.  While  the  earlier  experiments  are  open  to 
criticism  in  some  particulars,  'on  the  whole  the  conclusion  ap- 
pears warranted  that  the  digestibility  of  forage  is  not  very 
materially  diminished  by  the  simple  removal  of  water  and  that 
the  lower  value  of  ordinary  dry  roughage  as  compared  with  green 
forage  is  largely  due  to  differences  in  maturity  and  composition. 
730.  Cutting  of  roughage.  —  The  digestibility  of  coarse  fod- 
ders is  not  increased  by  cutting,  and,  indeed,  it  would  be  dif- 
ficult to  conceive  how  that  process  could  have  such  an  effect, 
since  in  either  case  the  feed  is  comminuted  during  mastication 
to  practically  the  same  extent.  This  is  strikingly  shown  in 
experiments  by  Kellner3  in  which  the  preparation  of  straw 
and  chaff  was  carried  to  the  extent  of  grinding  it  to  a  fine  meal. 
Table  182  shows  his  comparison  between  wheat  straw  and  barley 
straw  cut  into  inch  and  a  half  lengths  or  finely  ground. 

TABLE  182.  —  DIGESTIBILITY  CUT  AND  FINELY  GROUND 


ORGANIC 
MATTER 

CRUDE 

PROTEIN 

CRUDE 
FIBER 

NITRO- 
GEN-FREE 
EXTRACT 

ETHER 
EXTRACT 

Wheat  straw 
Cut 

% 
ic  8 

% 
-18.3 

% 

A  A   O 

% 
30  8 

% 
16  7 

Finely  ground  .          ... 

34  8 

-    21.6 

AI   Q 

3O  7 

30  2 

Barley  straw 
Cut 

AQ    8 

34  4. 

52  O 

CQ  O 

32  ^ 

Finely  ground  

48.9 

IQ.I 

52.6 

49.4 

36-9 

731.  Grinding  of  grain.  —  The  outer  coats  of  seeds  are  re- 
sistant to  solvents,  their  purpose  being  to  protect  the  seeds  from 
external  influences.  When  whole  grain  is  fed,  especially  in  large 

JPenna.  Expt.  Sta.,  Rpt.  1888,  p.  60;  Agricultural  Science,  3,  295. 

2Landw.  Vers.  Stat.,  75  (1911),  321. 

3  Ernahrung  landw.  Nutztiere,  6th  Ed.  p.  266. 


RELATIVE  VALUES  OF  FEEDING  STUFFS     625 

amounts  to  greedy  feeders  or  to  animals  with  imperfect  teeth, 
more  or  less  of  it  escapes  mastication  and,  protected  by  the 
outer  coats,  passes  through  the  digestive  tract  relatively  unacted 
upon.  Such  apparently  intact  grains  of  corn,  oats,  etc.,  still 
capable  of  germination,  are  a  familiar  sight  in  the  droppings  of 
heavily  fed  animals. 

Such  visible  losses,  however,  are  not  confined  to  the  feeding 
of  whole  grain  but,  although  less  obvious,  extend  to  cracked  or 
crushed  grain  as  well.  If,  for  example,  the  feces  of  full-fed 
cattle  receiving  cracked  com  or  other  grain  be  washed  out,  a 
considerable  amount  of  fragments  of  grain  may  be  recovered, 
the  amount  depending  upon  the  total  quantity  fed  and  the  con- 
sequent rapidity  with  which  it  passes  through  the  digestive 
tract.  Moreover,  it  is  evident  that  the  mechanical  separation 
by  washing  is  necessarily  imperfect.  Not  only  may  the  sieve 
hold  back  other  things  than  fragments  of  grain,  but  it  is  like- 
wise clear  that  any  undigested  fragments  of  the  latter  which 
are  smaller  than  the  meshes  of  the  sieve  will  pass  through  and 
be  lost,  so  that  fine  meal  or  well-masticated  grain  might  suffer 
a  greater  loss  through  incomplete  digestion  than  would  be 
indicated  by  such  tests.  While  it  is  to  be  supposed  that  smaller 
fragments  will  undergo  more  rapid  solution  in  the  digestive 
tract  than  larger  ones,  it  is  evident  that  the  rapidity  of  passage 
through  the  organs  is  an  important  factor  and  that  even  com- 
paratively small  bits  may,  under  some  circumstances,  escape 
complete  digestion,  while  on  the  other  hand,  with  light  feeding, 
whole  grain  might  be  almost  as  well  digested  as  when  ground. 
Qualitatively,  the  results  reached  by  washing  out  the  feces  are 
of  great  interest,  but  they  may  readily  be  misleading  as  regards 
the  actual  advantage  of  grinding. 

Surprisingly  few  investigations  upon  the  relative  digesti- 
bility of  ground  and  unground  grain  have  been  reported.  Jor- 
dan and  Hall,1  in  their  compilation  of  American  digestion  ex- 
periments up  to  1900,  present  two  comparisons  with  horses 
and  two  with  swine,  all  of  which  show  the  ground  grain  to  be 
more  digestible  than  the  unground,  the  difference  with  respect 
to  the  dry  matter  ranging  from  3.3  to  14  per  cent. 

Gay,2  in  experiments  upon  oats  with  a  horse  weighing  about 

1 U.  S.  Dept.  Agr.,  Office  Expt.  Stas.,  Bui.  77,  p.  97- 
a  Centbl.  Agr.  Chem.,  25  (1896),  729. 

2  S 


626 


NUTRITION  OF   FARM   ANIMALS 


340  kilograms  (750  Ib.)  and  receiving  per  day  3  kilograms  of 
oats  and  2  kilograms  of  hay,  obtained  the  following  results :  — 

TABLE  183.  —  PERCENTAGE  DIGESTIBILITY  OF  OATS  BY  A  HORSE 


DRY 

MATTER 

ASH 

CRUDE 
PROTEIN 

CRUDE 
FIBER 

NITRO- 
GEN-FREE 
EXTRACT 

ETHER 
EXTRACT 

Whole  

64x3 

27.78 

71.^0 

42.00 

74.70 

40.00 

Crushed    .... 
Ground     .... 

68.58 
72.73 

31-97 
42.71 

79-15 
94.11 

48.87 
63.60 

74-99 
75-19 

59-46 
54.78 

Gain  by  crushing    . 

4-05 

4.19 

7.85 

6.87 

0.29 

18.56 

Gain  by  grinding    . 

8.20 

14-93 

22.81 

2  1.  60 

0.49 

13.88 

While  the  results  just  cited  are  more  or  less  variable,  and 
while  the  small  differences  in  the  digestibility  of  the  nitrogen-free 
extract  in  Gay's  experiments  seem  peculiar,  the  results  as  a 
whole  clearly  show  an  increased  digestibility  by  swine  and 
horses  as  a  result  of  grinding,  while  they  also  show  that  the 
difference  is  apparently  not  very  great  —  less  perhaps  than 
would  have  been  expected. 

Gay  also  reports  the  following  results  of  similar  experiments 
upon  a  sheep  weighing  81  kilograms  and  eating  500  grams  of 
oats  and  750  grams  of  alfalfa  hay:  — 

TABLE  184.  —  PERCENTAGE  DIGESTIBILITY  OF  OATS  BY  A  SHEEP 


DRY 

MATTER 

ASH 

CRUDE 
PROTEIN 

CRUDE 
FIBER 

NITRO- 
GEN-FREE 
EXTRACT 

ETHER 
EXTRACT 

Whole                 .     . 

66  24 

36  68 

7-7   O2 

4_r  r  r 

74  IO 

eg  2T 

Crushed    .... 

66.60 

26.55 

74.62 

45-03 

78.55 

64.81 

Ground     .... 

67.03 

27.14 

73-59 

44-75 

76.99 

72.20 

With  the  exception  of  the  ether  extract,  whose  digestibility 
it  is  difficult  to  determine  accurately  (165),  the  percentage 
digestibility  is  practically  identical  in  the  three  cases.  So  far 
as  a  single  experiment  goes,  therefore,  it  indicates  that  there  is 
no  advantage  in  grinding  oats  for  sheep.  Experiments  upon 


RELATIVE  VALUES  OF  FEEDING  STUFFS  627 

other  ruminants  and  with  other  feeding  stuffs  are  lacking,  but 
it  does  not  appear  surprising  that  a  ruminant  should  digest 
whole  grain  more  completely  than  a  non-ruminant.  As  a 
whole,  the  results  upon  the  influence  of  grinding  on  digestibility 
are  comparatively  meager  and  in  particular  they  afford  no  in- 
formation as  to  the  effect  of  variations  in  the  amount  fed  upon 
the  relative  digestibility  of  whole  grain  and  of  coarse  or  fine 
meal. 

732.  Acids.  —  The  extensive  use  of  silage  lends  interest  to 
the  question  of  the  influence  of  acids  on  the  digestibility  of 
feeding  stuffs. 

Weiske  1  compared  the  digestibility  of  meadow  hay  with  and 
without  the  addition  of  sulphuric  acid  (0.75  per  cent  SOs)  by  one 
sheep,  using  two  periods  on  each  ration,  and  obtained  almost 
absolutely  identical  results,  with  the  exception  of  a  slight  in- 
crease in  digestibility  of  the  ash  and  ether  extract  of  the  acidified 
hay.  Kellner  2  added  a  much  larger  proportion  of  lactic  acid 
(2.67  per  cent)  to  a  ration  of  hay  and  maize  fed  to  a  sheep  and 
likewise  observed  practically  no  effect  on  the  digestibility. 

Apparently,  then,  such  amounts  of  organic  acids  as  are  or- 
dinarily consumed  in  silage  and  other  feeds  are  without  effect 
on  digestion  in  the  case  of  ruminants  and  this  conclusion  is  to 
a  certain  extent  supported  by  the  general  results  of  experiments 
which  have  shown  that  ensiled  forage  is  fully  as  digestible  as 
the  same  material  carefully  dried.  The  amounts  of  acid  con- 
sumed under  normal  conditions  are  after  all  not  large  as  com- 
pared with  the  quantities  produced  in  the  rumen  and  neutral- 
ized by  the  saliva.  That  excessive  amounts  of  acids  may 
stimulate  peristalsis  and  so  produce  scouring  is  doubtless  true, 
and  it  may  be  presumed  that  other  species,  such  as  the  horse, 
for  example,  may  be  more  sensitive  to  acids  than  ruminants. 

733.  Condiments.  —  One  of   the  exaggerated  claims  made 
for  the  various  proprietary  condimental  feeds  is  that  they  are 
able  to  increase  materially  the  digestibility  of  rations  to  which 
they  are  added.     Not  the  slightest  scientific  basis  for  this  claim 
exists.     All  experimenters  agree  that  they  are  without  influence 
in  this  respect.     Recent  investigations  by  Fingerling,3  for  ex- 
ample, in  which  fennel,  anise,  fenugreek  and  malt  sprouts  were 

1  Jour.  Landw.,  33  (1885),  21.         2  Ernahrung  landw.  Nutztiere,  6th  Ed.,  p.  56. 
3  Landw.  Vers.  Stat.,  62  (1905),  41-57. 


628  NUTRITION  OF  FARM  ANIMALS 

added  both  to  ordinary  feeds  and  to  a  ration  made  up  of  ab- 
normally flavorless  materials  showed  no  effect  upon  the  per- 
centage digestibility. 

734.  Water  drinking.  —  Stress  has  been  laid  by  numerous 
writers  on  the  supposed  effect  of  water  drinking  on  digestion, 
particularly  by  the  horse.  It  has  been  asserted  that  drinking 
after  feeding  tends  to  dilute  the  gastric  juice  and  to  wash  the 
feed  out  of  the  stomach  and  the  feeder  has  been  advised  to 
water  his  animals  before  feeding  rather  than  after  feeding. 

Even  were  the  supposed  facts  true,  it  is  questionable  whether 
the  conclusions  drawn  would  be  warranted,  since  the  stomach, 
far  from  being  the  sole  organ  of  digestion,  serves  largely  as  a 
sort  of  preliminary  reservoir  (119),  and  the  extensive  intestines 
of  farm  animals  afford  ample  opportunity  for  the  digestion  of 
any  substances  which  may  escape  action  in  the  stomach.  As 
a  matter  of  fact,  however,  no  such  washing  out  or  degree  of 
dilution  occurs  as  has  been  supposed.  As  has  already  been 
stated  (131),  the  contents  of  the  stomach  are  semi-solid  rather 
than  liquid  and,  as  shown  by  their  stratification,  much  less 
mixing  of  them  takes  place  than  is  sometimes  imagined.  Scheu- 
nert x  has  shown  that  in  the  horse  the  larger  part  of  the  water 
drunk  passes  along  the  walls  of  the  stomach  and  around  its 
contents  and  is  quite  promptly  discharged  into  the  small 
intestine.  This  is  especially  the  case  when  the  stomach  is 
well  filled  with  feed.  In  the  contrary  case  more  water  is 
retained,  but  in  no  case  did  the  total  dilution  of  the  entire 
stomach  contents  exceed  about  10  per  cent.  Moreover,  the 
water  which  enters  the  duodenum  is  rather  rapidly  resorbed 
and  has  no  material  effect  in  the  transportation  of  feed  into  the 
large  intestine. 

In  view  of  these  facts  it  is  not  surprising  to  find  that  the 
few  digestion  trials  which  have  been  made  show  no  evidence  of 
a  decrease  in  digestibility  as  a  result  of  drinking  after  eating. 

Gabriel  and  Weiske 2  in  experiments  on  two  sheep  found  no  signifi- 
cant difference  in  the  percentage  digestibility  of  a  ration  of  oats  and 
hay,  whether  the  water  was  given  before  or  after  feeding  or  kept  con- 
stantly before  the  animals.  The  percentage  digestibility  of  the 
organic  matter  was:  — 

1  Arch.  Physiol.  (Pfliiger),  144  (1912),  411 ;   151  (1913),  39&. 

2  Landw.  Vers.  Stat.,  45  (1895),  311. 


RELATIVE  VALUES  OF   FEEDING  STUFFS 


629 


SHEEP  I 

SHEEP  II 

Water  constantly  before  the  animals      .     .     . 
Watered  before  feeding    
Watered  after  feeding 

64.2 
61.4 
62  ^ 

63.3 
64.4 
62  8 

Tangl,1  in  a  number  of  experiments  upon  four  different  horses, 
found  that  when  watered  before  drinking,  the  consumption  of  water 
was  irregular  and  was  less  than  when  they  were  watered  during  or 
after  feeding,  and  that  the  corresponding  digestibility  was  also  less 
in  nearly  every  case.  Suggestive  in  this  connection  are  the  results  of 
Foster  and  Lambert,2  who  found  that  in  the  dog  a  restricted  supply  of 
water  tended  to  decrease  the  secretion  of  gastric  juice.  The  fore- 
going results  on  animals  seem  to  be  in  general  accord  with  those  of 
Hawk's  extensive  studies  on  the  effects  of  water  drinking  in  man. 


1  Jahresber.  Agr.  Chem.,  28  (1899),  661. 


2Expt.  Sta.  Rec.,  25  (1911),  16. 


CHAPTER  XVII 

THE   PRODUCTION  VALUES  OF  FEEDING  STUFFS 
§  i.  GENERAL  CONSIDERATIONS 

735.  Definition.  —  By    the    production   values    of    feeding 
stuffs,  as  distinguished  from  the  relative  values  discussed  in 
the  last  chapter,  is  meant  the  actual  effect  produced  by  a  unit 
weight  of  the  substance  in  maintaining  an  animal  or  in  sup- 
porting the  processes  of  growth  and  fattening  or  of  milk  or  work 
production.     That  such  production  values  will   also  express 
relative  values  scarcely  needs  mention. 

Even  at  their  best,  comparisons  based  on  the  "  digestible 
nutrients,"  such  as  have  been  in  vogue  for  many  years  and 
have  become  familiar  to  all  students  of  the  subject,  can  show 
only  the  relative  and  not  the  absolute  values  of  feeding  stuffs. 
It  is  true  that  to  the  extent  to  which  it  may  be  assumed  that 
the  digestible  nutrients  as  determined  by  analyses  and  digestion 
experiments  actually  consist  of  proteins,  carbohydrates  and 
fats,  their  amount  may  furnish  a  useful  clue  to  the  nutritive 
value  of  the  material  consumed.  Even  then,  however,  it  affords 
no  quantitative  measure  of  the  results  to  be  expected,  while  in 
the  case  of  most  feeding  stuffs,  as  appeared  in  Chapters  II  and 
III,  the  actual  nature  of  the  digested  material  has  been  but  very 
incompletely  investigated.  Neither  the  chemistry  of  feeding 
stuffs  nor  the  behavior  of  their  various  constituents  in  metab- 
olism is  sufficiently  well  known  to  serve  as  the  basis  for  any 
trustworthy  estimate  of  their  actual  nutritive  effect.  The  lat- 
ter can  be  determined  only  by  a  direct  trial  with  the  animal, 
and  during  the  past  two  decades  considerable  progress  has  been 
made  in  this  direction. 

736.  Determination  of  production  values.  —  By  definition 
the  production  value  is  the  effect  produced  upon  the  animal  by 
a  unit  of  the  feed  under  consideration.     The  general  methods 

630 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS      631 

for  ascertaining  this  effect  have  been  considered  in  Chap- 
ter VI.  It  was  there  shown  that  neither  the  gain  nor  loss  of 
live  weight  or  the  gross  weight  of  product  is  a  sufficiently 
accurate  measure  of  it  (281-283,  604)  and  that  the  attain- 
ment of  exact  results  requires  the  employment  of  some  form 
of  the  balance  experiment  (285),  based  on  the  conception  of 
the  balance  of  nutrition.  According  to  this  conception,  the 
production  values  of  a  feeding  stuff  for  various  purposes  are 
measured,  either  by  the  extent  to  which  it  can  prevent  a 
loss  of  protein,  ash  and  fat  from  the  body  during  maintenance 
or  work  or  can  support  the  storage  of  these  ingredients  in  the 
body  or  the  milk.  It  was  also  pointed  out  in  the  same  chapter 
that  the  investigations  of  the  last  thirty  years  have  shown  that 
the  problem  may  be  advantageously  studied  from  the  stand- 
point of  energetics  and  that  in  this  way  the  expression  of  the 
results  may  be  notably  simplified  and  unified.  From  this  stand- 
point the  feed  is  regarded  as  a  supply  of  ash  and  protein  (or 
amino  acids)  on  the  one  hand  and  of  energy  on  the  other  and 
its  effect  is  similarly  expressed  by  the  gain  or  loss  by  the  body 
of  protein  and  ash  and  of  chemical  energy  respectively.  We 
may  distinguish,  therefore,  between  production  values  for  pro- 
tein, for  ash,  and  for  energy. 

737.  Two  aspects  of  feed  supply.  —  For  a  clear  conception 
of  the  nature  and  significance  of  the  production  values  of  feed- 
ing stuffs,  however,  it  is  essential  to  distinguish  between  two 
aspects  or  functions  of  the  feed  supply. 

In  the  past  the  feed  has  been  regarded  chiefly  as  the  source  of 
the  material  necessary  for  the  constructive  processes  going  on 
in  the  body  and  of  the  energy  required  to  support  its  metabolic 
activities.  It  supplies  ash  to  maintain  or  increase  the  mineral 
matter  of  the  body,  protein  (or  amino  acids)  to  build  up  its 
tissues  or  supply  the  protein  of  milk,  energy  to  support  the 
vital  activities  of  the  various  organs.  This  aspect  of  the  mat- 
ter has  been  the  prominent  one  in  the  preceding  chapters  of 
this  work. 

Recent  investigation,  however,  is  bringing  into  prominence 
another  class  of  influences  exerted  by  the  feed  upon  the  or- 
ganism. The  studies  upon  the  "  vitamins,"  "  accessory  in- 
gredients," "  growth  substances,"  "  stimulating  substances," 
"  specific  effects  of  feeds,"  etc.,  which  have  been  several  times 


632  NUTRITION  OF  FARM  ANIMALS 

referred  to  in  Part  III  are  rendering  it  increasingly  evident  that, 
quite  aside  from  its  value  as  a  supply  of  structural  material  and 
of  energy,  the  nature  of  the  feed  may  profoundly  influence 
the  course  and  intensity  of  the  metabolic  processes.  In  par- 
ticular it  appears  that  the  absence  of  certain  as  yet  ill-defined 
substances  may  constitute  a  limiting  factor,  particularly  in 
growth,  or  may  lead  to  the  development  of  specific  diseases, 
while,  on  the  other  hand,  McCollum's  observations  on  the  ex- 
clusive use  of  wheat  products  (499)  seem  to  indicate  that  similar 
effects  of  a  more  or  less  toxic  character  may  follow  the  exces- 
sive consumption  of  feeding  stuffs  ordinarily  regarded  as  health- 
ful. It  is  important,  therefore,  to  secure  as  definite  a  concep- 
tion as  possible  of  the  significance  of  these  new  facts  in  their 
relation  to  the  older  conceptions  of  production  values. 

738.  Significance  of  "  accessory  ingredients."  It  is  clear 
that  the  "  accessory  ingredients  •"  (using  this  simply  as  a  con- 
venient summary  term  for  the  various  classes  of  substances 
indicated  in  the  last  paragraph)  influence  the  nutritive  value 
of  a  feeding  stuff  in  an  essentially  different  fashion  than  does 
the  quantity  of  available  ash,  protein,  and  energy  which  it 
supplies.  The  latter  limits  the  amount  of  production  which  the 
feeding  stuff  can  support ;  the  presence  or  absence  of  the  former 
may  determine  the  extent  to  which  this  potential  value  is  actu- 
ally realized.  Thus  in  Chapter  XI,  experiments  by  Osborne  and 
Mendel  and  by  Hart  and  McCollum  (498,  499)  were  described 
which  show  that  a  mixture  of  pure  nutrients  may  be  prepared 
which  shall  contain  an  abundant  supply  of  complete  proteins, 
of  ash  and  of  energy  but  upon  which  young  animals  (rats)  fail'to 
grow,  while  the  addition  to  such  a  mixture  of  minute  amounts 
of  substances  associated  with  certain  fats  enables  the  rations  to 
support  normal  growth.  In  some  aspects  of  the  matter,  these 
"  accessory  ingredients  "  might  be  crudely  compared  with  the 
lubricants  of  a  machine,  which  of  themselves  furnish  neither 
power  nor  material,  but  which  enable  power  derived  from  the 
consumption  of  fuel  to  be  more  efficiently  used  and  therefore 
conduce  to  the  production  of  a  larger  output. 

A  lack  of  lubricants  in  the  case  just  supposed  might  conceiv- 
ably affect  the  output  of  a  machine  in  one  or  both  of  two  ways. 
The  undue  friction  might  slow  down  the  machine  as  a  whole 
so  that  less  raw  material  would  pass  through  it  in  a  given  time, 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS     633 

or  it  might  affect  specifically  certain  more  delicate  parts  of  the 
machine  and  so  reduce  the  efficiency  of  the  machine  and  cause  it 
to  yield  less  finished  product  per  unit  of  raw  material  consumed. 

In  which  of  these  two  ways  a  deficiency  in  "  accessory  sub- 
stances "  affects  the  nutrition  of  an  animal  does  not  appear  to 
have  been  determined.  It  would  seem  probable,  however,  that, 
in  the  case  of  a  young  animal,  for  example,  a  deficient  dietary 
acts  to  slow  down  or  stop  the  whole  group  of  anabolic  processes 
involved  in  growth.1  The  organs  would  thus  be  rendered  in- 
capable of  converting  a  normal  daily  amount  of  feed  into  body 
substances  and  a  corresponding  decrease  in  feed  consumption 
would  presumably  follow.  In  such  a  case  it  is  quite  conceivable 
that  such  feed  as  was  actually  eaten  in  excess  of  the  maintenance 
requirement  might  be -just  as  efficient  in  producing  gain  and 
have  as  great  a  production  value  per  unit  as  in  a  normal  ration. 
In  other  words,  it  is  conceivable  that  lack  of  the  "  accessory  sub- 
stances "  may,  in  a  sense,  affect  the  economic  rather  than  the 
physiological  efficiency  of  the  ration.  The  writer  has  failed  to 
note  any  experiments  in  which  this  aspect  of  the  matter  has  been 
considered.  In  practically  all  reported  investigations  upon  the 
influence  of  "  accessory  substances,"  the  feed  consumption  has 
been  regulated  by  the  appetite  of  the  animal  and  in  many  in- 
stances has  not  even  been  reported. 

The  undoubted  importance  of  the  accessory  ingredients  of 
feeding  stuffs  has  led,  on  the  part  of  some  writers,  to  a  tendency 
which  as  yet  appears  hardly  justified  to  minimize  the  signifi- 
cance of  the  production  values  in  the  older  sense.  The  subject 
is  too  new  and  the  field  too  broad  to  warrant  dogmatic  con- 
clusions, but  it  still  remains  true  that  the  prime  function  of  a 
feeding  stuff  is  to  supply  structural  material  and  energy  for 
the  body,  and  its  potentialities  in  this  respect  are  expressed  in 
its  production  values.  That  the  results  attained  by  its  use 
in  practice  are  affected  by  other  considerations  has  long  been 
recognized.  Thus,  if  a  feeding  stuff  is  unpalatable  for  some 
reason  and  is  not  eaten  freely,  the  portion  consumed  may 
show  a  high  nutritive  effect  per  unit  and  yet  the  use  of  the 
feed  be  inadvisable.  The  presence  of  toxic  substances  might 

1  Naturally  such  an  effect  might  be  brought  about  by  a  retardation  of  certain 
specific  metabolisms  upon  which  the  whole  growth  process  depended  and  the  spe- 
cific metabolisms  affected  might  differ  in  different  cases. 


634  NUTRITION  OF  FARM  ANIMALS 

prevent  the  use  of  a  feed  in  sufficient  amounts  to  be  profitable 
and  yet  the  nutritive  effect  of  the  feed  within  the  limits  of 
tolerance  might  be  considerable. 

Production  values,  then,  if  determined  by  means  of  balance 
experiments  made  under  normal  conditions,  are  to  be  regarded 
as  showing  the  potential  values  of  feeding  stuffs  as  sources  of 
matter  and  energy,  i.e.,  their  worth  as  constituents  of  a  ration 
which  contains  sufficient  amounts  of  whatever  "  accessory  in- 
gredients "  are  necessary  to  ensure  the  normal  course  of  metab- 
olism. The  study  of  "  accessory  substances  "  in  the  broadest 
sense  of  the  term  has  revealed  an  additional  and  apparently  very 
important  group  of  factors  influencing  the  extent  to  which  the 
potentialities  of  feeding  stuffs  are  actually  utilized.  It  is  pos- 
sible that  in  the  future  there  must  be  added  to  the  require- 
ments already  outlined  for  ash,  protein  (or  amino  acids)  and 
energy  for  the  various  purposes  of  feeding,  the  requirements  for 
the  "  accessory  substances "  necessary  to  secure  the  most 
efficient  functioning  of  the  cells  and  organs  of  the  body. 

§  2.  PRODUCTION  VALUES  AS  REGARDS  ENERGY  —  NET 
ENERGY  VALUES 

739.  Recapitulation.  —  The  consideration  of  the  processes  of 
nutrition  in  Part  II,  and  in  particular  the  study  of  metabolism 
and  of  the  balance  of  nutrition  in  Chapters  V  and  VI,  has 
shown  that  the  animal  body  is  primarily  a  transformer  of 
chemical  energy  and  that  quantitatively  the  most  important 
function  of  the  feed  is  to  supply  this  energy.  In  the  several 
chapters  of  Part  III  the  conception  of  net  energy  values  was 
developed  and  the  requirements  for  net  energy  by  different 
species  of  farm  animals  and  for  different  purposes  were  dis- 
cussed. It  is  apparent  from  those  discussions  that  the  net 
energy  value  is  only  another  name  for  the  production  value  of 
a  feeding  stuff  as  regards  energy  as  defined  in  the  preceding 
section.  It  appears  desirable  at  this  point,  therefore,  to  re- 
capitulate the  general  facts  regarding  the  energetics  of  the 
animal  body  which  are  contained  in  previous  chapters,  and 
to  consider  in  greater  detail  their  bearing  upon  the  production 
values  of  feeding  stuffs,  even  at  the  expense  of  a  certain  amount 
of  repetition. 


THE   PRODUCTION  VALUES  OF  FEEDING  STUFFS     635 

740.  Gross  energy.  —  The  energy  supply  of  an  animal  is 
contained  in  its  feed  as  chemical  energy,  and  the  maximum 
amount  which  any  substance  can  furnish  for  the  vital  activities 
by  its  oxidation  in  the  body  is  measured  by  its  heat  of  com- 
bustion.    This  has  been  called  its  gross  energy  (315)  to  avoid 
the  implication  that  it  represents  the  total  amount  of  energy 
associated  with  the  substance. 

741.  Losses  of  energy.  —  It  rarely,  if  ever,  happens,  how- 
ever, that  this  maximum  effect  is  realized.     In  practically  every 
case  a  larger  or  smaller  proportion  of  the  chemical  energy  of 
the  feed  escapes  unutilized.     These  losses  of  energy  are  of  two 
general  classes. 

First,  a  portion  of  the  chemical  energy  of  the  feed  fails  to  be 
transformed  at  all,  leaving  the  body  as  chemical  energy  in  the 
visible  excreta  and  in  the  combustible  gases  arising  from  gastric 
and  intestinal  fermentations. 

Second,  another  portion  of  the  chemical  energy  of  the  feed  is 
indeed  transformed,  but  at  ordinary  temperatures  virtually  re- 
sults merely  in  a  superfluous  heat  production.  It  is  true  that 
the  metabolism  consequent  upon  feed  consumption  is  not  only 
unavoidable  but  may  be  regarded  as  a  necessary  expenditure  of 
energy  for  the  support  of  the  activities  connected  with  digestion 
and  assimilation.  Nevertheless,  from  the  standpoint  of  the 
net  gain  or  loss  by  the  organism  this  portion  of  the  feed  energy, 
which  ultimately  takes  the  form  of  heat  and  escapes  from  the 
body,  must  be  regarded  as  a  loss. 

The  losses  of  chemical  energy 

742.  Losses  in  feces.  —  Chemical  energy  escapes  in  the  feces 
both  in  the  undigested  feed  residues  which  they  contain  and 
in  the  excretory  products  which  they  carry.     While  the  latter 
portion  is  not  derived  immediately  from  the  feed  consumed, 
but  constitutes  a  loss  of  incompletely  katabolized  matter,  it 
must,  none  the  less,  be  included  in  estimating  the  net  effect 
of  a  ration  on  the  energy  balance  of  the  body. 

With  herbivorous  animals,  the  excretion  in  the  feces  con- 
stitutes the  greatest  loss  of  chemical  energy,  and  the  one  which 
varies  most  as  between  different  feeding  stuffs  or  different  species 
of  animals,  as  is  apparent  from  the  results  recorded  in  Table  187 


636  NUTRITION    OF    FARM    ANIMALS 

(749).  This  is  especially  true  of  the  energy  of  roughages,  which 
contain  much  indigestible  matter,  but  even  with  the  more  di- 
gestible materials  the  loss  through  the  feces  is  relatively  con- 
siderable. With  swine  it  is  relatively  less  than  with  herbivora 
because  the  former  animals  are  usually  largely  fed  on  concen- 
trates. The  influence  of  various  conditions  upon  the  losses  in 
the  feces,  i.e,,  upon  digestibility,  has  already  been  discussed  in 
§  3  of  the  previous  chapter. 

743.  Losses  in  urine.  —  The  urine  is  especially  the  vehicle 
for  the  removal  from  the  body  of  the  end  products  of  protein 
katabolism,  of  which  urea  is  the  most  familiar  and  frequently 
the  most  abundant.     Numerous  other  nitrogenous  substances, 
however,  are  contained  in  the  urine,  particularly  the  purins  and, 
in  herbivorous  animals,  hippuric  acid.     Moreover,  as  stated 
in  Chapter  V  (224,  225),  the  urine  of  herbivora  in  particular 
may  contain  relatively  considerable  quantities  of  non-nitrog- 
enous excretory  products  regarding  the  nature  of  which  little 
is  known.     All  these  substances  carry  off  a  portion  of  the  gross 
energy  of  the  feed  as  unused  chemical  energy,  the  amount  of 
the  loss  being  measured  by  their  heats  of  combustion.    That 
the  extent  of  these  losses  cannot  be  satisfactorily  computed  from 
the  nitrogen  content  of  the  urine  has  already  been  pointed  out. 

The  loss  of  chemical  energy  in  the  urine,  as  appears  from 
Table  187,  constitutes  a  relatively  small  percentage  of  the 
total  loss.  As  would  be  expected,  it  is  quite  variable,  being 
higher  as  the  feed  supply  is  richer  in  protein,  and  lower  with 
relatively  indigestible  substances  where  the  loss  in  the  feces  is 
larger. 

744.  Fermentation  losses.  —  The  gaseous  products,  chiefly 
methane,  of  the  fermentation  of  the  carbohydrates  in  the  di- 
gestive tract  of  herbivora,  especially  of  ruminants,  carry  off  con- 
siderable amounts  of  unused  chemical  energy,   one  gram  «of 
methane,  for  example,  having  a  heat  of  combustion  of  13.344 
Calories. 

The  extent  to  which  the  carbohydrates  are  attacked  by  the 
methane  fermentation  appears  to  be  somewhat  variable. 
Armsby  and  Fries  x  have  observed  that  with  cattle  it  is  dis- 
tinctly greater  on  light  than  on  medium  or  heavy  rations  and 
the  same  authors  likewise  observed  a  single  instance  of  indi- 

1  Jour.  Agr'l  Research,  3  (1915),  445. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    637 

vidual  difference  in  this  respect  between  animals.  Recently 
Zuntz  and  his  associates  x  have  reported  striking  instances  in 
which  the  extent  of  the  methane  fermentation  in  particular 
has  been  markedly  affected  by  the  make-up  of  the  rations  and 
especially  by  the  order  in  which  the  feeds  were  consumed,  while 
Voltz  and  his  associates  2  have  laid  much  stress  upon  the  prac- 
tical importance  of  these  results.  No  such  marked  differences 
were  observed  in  Armsby  and  Fries'  experiments  but  the  range 
of  feeding  stuffs  used  was  not  so  wide.  It  is  perhaps  too  early 
to  judge  of  the  full  significance  of  Zuntz' s  results,  but  they  should 
at  least  serve  to  correct  the  notion,  more  or  less  subconsciously 
held  by  not  a  few,  of  digestion  as  a  perfectly  definite  process 
and  of  a  digestion  coefficient  as  a  sort  of  chemical  constant. 
On  the  other  hand,  however,  it  seems  quite  possible  to  over- 
estimate the  effect  of  such  variations  in  the  digestive  process 
upon  the  net  energy  values  of  feeding  stuffs.  On  the  whole, 
they  appear  to  be  of  far  less  significance  than  other  factors  to 
be  considered  later. 

The  percentage  of  the  gross  energy  which  is  lost  in  the  fer- 
mentation gases,  as  appears  from  Table  188  (749),  is  not  usually 
very  large.  It  is  naturally  greatest  in  the  case  of  feeding  stuffs 
rich  in  carbohydrates,  especially  the  easily  soluble  carbohydrates. 

745.  Computation  of  fermentation  losses.  —  While  the  ex- 
perimental determination  of  the  energy  losses  in  feces  and 
urine  is  a  comparatively  easy  task,  requiring  relatively  simple 
appliances,  the  determination  of  the  fermentation  losses  neces- 
sitates the  use  of  the  somewhat  complicated  and  costly  res- 
piration apparatus.  In  the  absence  of  such  an  apparatus,  how- 
ever, it  is  possible  to  compute  the  fermentation  losses  with  a  fair 
degree  of  accuracy  from  the  results  of  the  ordinary  digestion 
experiment.  The  methane  fermentation  attacks  chiefly  or 
wholly  the  carbohydrates  (135,  140)  and  in  the  case  of  cattle,  in 
particular,  it  has  been  shown  that  the  amount  of  methane  pro- 
duced is  in  general  proportional  to  the  amount  of  total  car- 
bohydrates (crude  fiber  and  nitrogen-free  extract)  digested. 

Kellner 3  in  forty-four  experiments  with  cattle  on  mixed 
rations  found  the  average  methane  excretion  to  be  4.2  grams 

1  Landw.  Jahrb.,  44  (1913),  765 ;  Landw.  Vers.  Stat.,  79-80  (1913),  781. 

2  Landw.  Jahrb.,  44  (1913),  685  ;  45  (1913),  325. 
8  Landw.  Vers.  Stat.,  53  (1900),  415. 


638  NUTRITION  OF  FARM  ANIMALS 

for  each  100  grams  of  total  carbohydrates  digested,  and  the 
estimated  results  for  ruminants  recorded  in  Table  188  for  the 
losses  in  methane  were  computed  on  that  basis.  With  the 
addition  of  later  unpublished  experiments,  Kellner's 1  aver- 
age was  increased  to  4.3  grams.  Later  experiments  by  Armsby 
and  Fries  2  have  given  slightly  higher  averages,  viz.,  4.8  grams 
for  roughages  and  4.7  grams  for  concentrates.  No  similar  re- 
sults for  the  smaller  ruminants  have  been  reported  but  probably 
it  may  >be  safely  assumed  that  the  average  for  cattle  is  substan- 
tially applicable  to  these  species  also. 

In  the  horse  the  principal  seat  of  the  methane  fermentation 
is  the  colon  and  ccecum  (128).  Since  the  more  soluble  carbo- 
hydrates of  the  feed  are  largely  or  entirely  digested  before  reach- 
ing these  organs,  methane  is  much  less  copiously  produced 
than  in  the  case  of  ruminants  and  may  be  regarded  as  derived 
chiefly  from  the  fermentation  of  crude  fiber. 

In  respiration  experiments  on  mixed  rations  of  oats,  hay 
and  straw,  Lehmann,  Zuntz  and  Hagemann 3  observed  as 
the  result  of  eight  rather  discordant  experiments  an  average 
total  excretion  of  methane  of  4.73  grams  per  100  grams  di- 
gested crude  fiber  and  in  addition  an  average  excretion  of  0.203 
gram  of  hydrogen  per  100  grams  digested  crude  fiber.  In 
more  recent  experiments,  Von  der  Heide,  Steuber  and  Zuntz,4 
using  a  Regnault-Reiset  respiration  apparatus  (298),  obtained 
for  the  methane  excretion  per  100  grams  digested  crude  fiber 
9.06  grams  on  hay  and  2.28  grams  on  straw  pulp.  Using 
the  average  of  these  rather  discordant  experiments,  the  fer- 
mentation losses  in  the  case  of  the  horse  may  be  approximately 
computed  from  the  amount  of  crude  fiber  digested. 

Swine  with  their  simpler  alimentary  canal  suffer  but  small 
losses  from  fermentation  in  the  digestive  tract. 

Fingerling,  Kohler  and  Reinhardt 5  found  the  amounts  of 
combustible  gases  excreted  too  small  to  be  determined  with 
their  form  of  Pettenkofer  apparatus.  Von  der  Heide  and 
Klein  6  in  three  experiments  with  a  Regnault-Reiset  apparatus 
obtained  the  following  results  :  — 

1  Ernahrung  landw.  Nutztiere,  6th  Ed.,  p.  94. 

2  Jour.  Agr'l  Research,  3  (1915),  p.  450.         3  Landw.  Jahrb.,  23  (1894),  125. 

4  Biochem.  Ztschr.,  73  (1916),  161.  5  Landw.  Vers.  Stat,  84  (1914),  197. 

6Biochem.  Ztschr.,  55  (1913),  195. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    639 


TABLE  185.  —  EXCRETED  BY  SWINE  PER  100  GRAMS  DIGESTED 
CARBOHYDRATES 


METHANE 
GRAMS 

HYDROGEN 
GRAMS 

Period  I                     

0.62 

O.I  I 

Period  II 

06^ 

O  O7 

Period  III                                

0.68 

o  04 

Average 

o  6^ 

O  O7 

Although  there  is  considerable  range  in  the  results  of  in- 
dividual experiments,  and  while  those  on  non-ruminants  are 
few  in  number,  nevertheless,  the  foregoing  figures  afford  a  basis 
for  an  approximate  estimate  of  the  losses  of  chemical  energy 
in  the  combustible  gases.  Summarizing  the  available  data 
and  computing  the  equivalent  quantities  of  energy,  it  appears 
that  the  following  average  deductions  may  be  made  from  the 
gross  energy  of  the  feed  for  the  fermentation  losses. 

TABLE  186.  —  FACTORS  FOR  COMPUTING  FERMENTATION  LOSSES 


EQUIVA- 

WEIGHT 

LENT 

ENERGY 

Per  100  grams  digested  carbohydrates 

Grams 

Cals. 

Ruminants  —  IMethane                    .               .... 

4-5 

60.  1 

Swine  —  JVIethane 

0.65 

8.7 

Hydrogen                            

0.07 

2.4 

Total                               

0.72 

II.  I 

Per  100  grams  digested  crude  fiber 

Horse  —  IVTethane                                       

4.7 

62.7 

Hydrogen        

O.2 

7.0 

Total      

4-9 

69.7 

Metabolizable  energy 

746.  Definition.  —  The  difference  between  the  chemical 
energy  of  the  feed  and  that  lost  in  the  excreta  shows  how  much 
of  the  former  is  capable  of  being  converted  into  other  forms  in 
the  body,  either  during  the  changes  which  the  feed  undergoes  in 


640 


NUTRITION  OF  FARM  ANIMALS 


the  digestive  tract  or  in  the  course  of  metabolism  in  the  tissues. 
As  stated  in  Chapter  VI  (323),  this  convertible  portion  of  the 
feed  energy  has  been  given  various  names  by  different  investi- 
gators, such  as  "  physiological  heat  value,"  "  fuel  value,"  "  avail- 
able energy,"  etc.,  but  following  a  suggestion  made  earlier  by 
the  writer  it  is  here  designated  as  "  metabolizable  energy." 

747.  Method  of  ,  determining. — •  As  is  apparent  from  the 
foregoing  paragraphs,  the  direct  determination  of  the  metab- 
olizable energy  of  a  feeding  stuff  or  ration  requires  the  meas- 
urement of  the  amounts  and  heats  of  combustion  of  the  feed 
and  of  the  solid,  liquid  and  gaseous  excreta  by  the  methods 
outlined  in  Chapter  VI.  These  quantities  being  known,  a 
simple  subtraction  gives  the  metabolizable  energy.  Thus  the 
results  of  the  experiment  used  as  an  illustration  in  Chapter  VI 
(322),  put  in  a  somewhat  more  detailed  form,  were  as  follows :  — 

TABLE  187.  —  EXAMPLE  OF  DETERMINATION  OF  METABOLIZABLE  ENERGY 


HEAT  OF 

FRESH 
WEIGHT 

DRY 

MATTER 

COMBUSTION 
or  DRY 
MATTER  PER 

ENERGY 
OF  FEED 

ENERGY 

OF 

EXCRETA 

GRAM 

Grams 

Grams 

Cals. 

Cals. 

Cals. 

Daily  feed 

Timothy  hay      .... 

6,988 

6,086 

4,556 

27,727 

— 

Linseed  meal      .... 

400 

354 

5,111 

1,811 

— 

Daily  excreta 

Feces    ....... 

16,619 

2,948 

4,831 

— 

14,243 

Urine 

4-2^7 



O  23O1 



I,2IO 

Methane   

,00  / 
142 

142 

w,  •6OV"' 

13,344 

— 

I,896 

Metabolizable  energy 

By  difference      .... 

— 

— 

— 

— 

I2,l89 

29,538 

29,538 

748.  Correction  for  gain  or  loss  of  protein.  —  In  the  foregoing 
experiment  the  animal  gained  15.2  grams  of  fat  and  66.6  grams  of 
protein  and  therefore  stored  up  in  its  body  equivalent  amounts  of 
energy,  viz., 

In  protein,  5.7  Cals.  X  66.6  =  380  Cals. 
In  fat,         9.5  Cals.  X  15.2  =  144  Cals. 
1  Per  gram  fresh  urine. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    641 

The  144  Cals.  of  energy  contained  in  the  fat,  however,  although 
not  actually  transformed  into  other  forms  of  energy,  were  capable  of 
such  transformation  had  the  demands  of  the  organism  required  it, 
and  therefore  constitute  part  of  the  metabolizable  energy  of  the  feed. 
With  the  380  Cals.  contained  in  the  protein  stored  up,  however,  the 
case  is  different.  Had  these  66.6  grams  been  katabolized,  part  of 
their  energy  would  have  escaped  in  the  resulting  nitrogeneous  meta- 
bolic products.  According  to  Rubner  each  gram  of  urinary  nitrogen 
derived  from  lean  meat  is  equivalent  to  7.45  Cals.  of  chemical  energy. 
The  katabolism  of  the  66.6  grams  of  protein,  therefore,  would  have  in- 
creased the  chemical  energy  of  the  urine  by  83  Cals.,  while  only  297 
Cals.  would  have  been  transformed.  This  amount  of  83  Cals.  must 
consequently  be  added  as  a  correction  to  the  urinary  energy  as  measured 
in  computing  the  metabolizable  energy.  In  case  of  a  loss  of  protein 
from  the  body  a  similar  correction  must  evidently  be  subtracted. 

When  a  respiration  apparatus  for  the  determination  of  the 
combustible  gases  is  not  available,  their  amount  may  be  esti- 
mated from  the  digestible  carbohydrates  in  the  manner  al- 
ready outlined  (745) ,  so  that  it  is  possible  to  estimate  the  metab- 
olizable energy  with  a  considerable  degree  of  accuracy  from  the 
results  of  an  ordinary  digestion  experiment  to  which  has  been 
added  the  collection  of  the  urine  and  determinations  of  the  heats 
of  combustion  of  the  visible  excreta.  The  additional  labor 
thus  required  is  so  small  that  it  is  to  be  hoped  that  in  future 
digestion  experiments  it  may  be  undertaken  whenever  possible 
and  that  in  this  way  more  extensive  data  may  be  secured  re- 
garding the  metabolizable  energy  of  feeding  stuffs.  While 
such  results  do  not  show  the  production  values  of  the  rations 
(750),  they  constitute  an  important  step  toward  their  more 
exact  determination. 

749.  Experimental  Results.  —  There  are  on  record  a  some- 
what limited  number  of  experiments  with  cattle  and  a  few 
with  swine  in  which  the  losses  of  energy  in  the  feces,  urine  and 
methane  respectively  have  been  determined  directly,  while  in 
a  considerably  larger  number  the  losses  of  methane  have  been 
estimated  from  the  digestible  carbohydrates  (crude  fiber  plus 
nitrogen-free  extract)  in  the  manner  just  described.  The  re- 
sults of  these  experiments  are  recorded  in  Table  iSS,1  which 
shows  the  percentages  of  the  gross  energy  which  were  carried 

1  This  table  is  not  claimed  to  be  an  exhaustive  compilation  of  data,  but  is  be- 
lieved to  be  fairly  complete. 
2  T 


642 


NUTRITION  OF  FARM  ANIMALS 


off  in  the  several  excreta  and,  by  difference,  the  percentages 
which  were  metabolizable.  The  metabolizable  energy  per 
gram  of  digestible  organic  matter  is  also  added,  since,  as  will 
appear  subsequently,  it  forms  a  convenient  basis  for  the  com- 
putation of  metabolizable  energy  when  direct  determinations 
of  it  are  not  available. 


TABLE  188.  —  APPARENT  METABOLIZABLE  ENERGY 


PERC 

ENTAGE  Lc 

SSES 

w 

%8 

£ 

W    r£ 

AUTHOR 

w 

. 

In 
Feces 

In  Urine 

In 
Meth- 
ane 

f 

15 

CATTLE 
Roughages 

% 

% 

% 

% 

Cals. 

Meadow  hay    

Kellner 

40.96 

5-71 

6.77 

46.56 

3-Soi 

Meadow  hay    

Tangl,  et  al. 

44.6 

5-5 

6.8i 

43-1 

3-437 

Timothy  hay 

Armsby  and  Fries 

46.4 

,  8 

7-3 

42.5 

Red  clover  hay     .... 

Armsby  and  Fries 

41.9 

O-° 

6.8 

6.5 

44-8 

3^486 

Mixed    timothy    and    red 

clover  hay     

Armsby  and  Fries 

43-9 

5-2 

7-4 

43-5 

3-390 

Alfalfa  hay  

Armsby  and  Fries 

44.1 

5-8 

6.2 

43-9 

3-605 

Hay  from  irrigated  meadows 

Tangl,  el  al. 

47-5 

3-o 

6.61 

42-9 

3.600 

Ensiled  hay      

Tangl,  et  al. 

62.5 

o.4(?) 

4.91 

32-2 

3-698 

Oat  straw    

Kellner 

56.8 

2.1 

5-3 

35-8 

3-740 

Wheat  straw     

Kellner 

58.2 

2.4 

8-3 

3I-I 

3-310 

Straw  pulp  

Kellner 

12.8 

-0.8 

12.5 

75-5 

3-640 

Maize  stover    

Armsby  and  Fries 

42.8 

4.2 

7-9 

45-1 

3-450 

Average   

3-529 

Concentrates 

Maize  meal       

Armsby  and  Fries 

13-3 

S-i 

IO.O 

71.6 

3-797 

Wheat  bran      

Armsby  and  Fries 

31-8 

5-4 

7-4 

55-4 

3-954 

Hominy  chop  

Armsby  and  Fries 

12.2 

3-8 

9-2 

74-8 

4-075 

Mixed  grains  No.  i    .     .     . 

Armsby  and  Fries 

19.2 

7-2 

8.2 

65.4 

3.910 

Mixed  grains  No.  2   ... 

Armsby  and  Fries 

22.7 

4-4 

8.1 

64.8 

3.879 

Millet      

Tangl,  et  al. 

34-6 

3-4 

7-71 

54-3 

3-787 

Palmnut  meal  

Voltz,  et  al. 

19-3 

-   2.02 

6.91 

75-8 

4-849 

Distillers'       slop        (from 

potatoes)       

Voltz,  et  al. 

61.1 

4.5  2 

5-41 

29.0 

2.703 

Beet  molasses  

Voltz,  et  al. 

—  46.5 

-3-02 

I3-71 

135-8 

5-361 

Beet  molasses  

Kellner 

9-9 

2-9 

"•3 

75-9 

3-473 

Distillers'      residue      from 

grapes  +  beet  molasses  . 

Tangl,  et  al. 

59-1 

3-4 

3-8' 

33-7 

4-519 

Pumpkins    

Tangl,  et  al. 

20.1 

2.8 

6.91 

70.2 

4-287 

Starch                              .     . 

Kellner 

17.6 

—  0.7 

9-2 

73-9 

3  '603 

Wheat  gluten  

Kellner 

20.  2 

I3-I 

O.I 

66.6 

4.792 

Average    

4.078 

1  Estimated. 


2  Not  corrected  to  N.  equilibrium. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS     643 
TABLE  1 88  — APPARENT  METABOLIZABLE  ENERGY  (Continued) 


- 

PERCI 

,NTAGE  LOS 

SES 

. 

$• 

I 

|P 

AUTHOR 

ap 

In 
Feces 

In 

Urine 

In 

Meth- 
ane 

o  « 

SHEEP 
Roughages 

% 

% 

% 

% 

Cals. 

Meadow  hay    

Tangl,  et  al. 

46.6 

4.8 

6.2  i 

42.4 

3-559 

Meadow  hay    

Voltz,  et  al. 

43-5 

4-82 

6.3  1 

45-4 

3.611 

Hay  from  peat  meadows    . 

Tangl,  et  al. 

59-4 

4.1 

4.81 

31-6 

3-544 

Hay  from  alkali  soil  .     .     . 

Tangl,  et  al. 

52.9 

4-1 

5-51 

37-5 

3.601 

Hay  from  same,  irrigated  . 

Tangl,  et  al. 

40.4 

4.1 

n.41 

44.1 

3.288 

Alpine  hay  

Tangl,  et  al. 

39-2 

4.1 

6.9l 

49.8 

3-765 

Average   

35-6i 

Alfalfa  hay  

Tangl,  et  al. 

32.5 

4.1 

5-4  1 

58.0 

4-467 

Average   

3.691 

Dried  potato  vines    .     .     . 

Voltz,  et  al. 

43-2 

3-5  2 

5-3  l 

48.0 

4.  182 

Same  with  fruit     .... 
Hay  and  dried  potato  vines 

Voltz,  et  al. 
Voltz,  et  al. 

45-9 
41-3 

3-82 

4.81 
6.3l 

45-5 
47-2 

4-319 

•2    62O 

Hay    and    ensiled    potato 

£.\JHJ 

vines    

Voltz,  el  al. 

42.2 

S-92 

5-9  * 

46.0 

g 

Wheat  straw    

Voltz,  et  al. 

74-9 

4-1  2 

4.6! 

16.4 

2.378 

Average   

3.655 

Concentrates 

Oats    

Tangl,  et  al. 

35-5 

4.1 

6.61 

53-8 

3-973 

Millet      

Tangl,  et  al. 

30.2 

7.1 

8.2  i 

54-5 

3.405 

Corn-and-cob  meal    .     .     . 

Tangl,  et  al. 

31-0 

2-9 

8.2! 

57-9 

,  8*6 

Palmnut  meal  

Voltz,  et  al. 

35-o 

4-5  2 

6.3  i 

54-2 

O-°OL' 

3-977 

Lentils     . 

Voltz,  et  al. 

7.O 

12.92 

8.7! 

7I.J. 

Distillery  slop  from   pota- 

4.079 

toes     

Voltz,  et  al. 

23-2 

7.62 

6.3! 

62.9 

4.383 

Beet  molasses  

Voltz,  et  al. 

18.6 

17-3 

7-9 

56.29 

3-124 

Average   

3-825 

HORSES 

Roughages 

Meadow  hay    

Tangl,  et  al. 

55-1 

3-6 

1.9! 

39-4 

3.707 

Hay  from  peat  meadow 

Tangl,  et  al. 

66.1 

3.7 

o.8i 

29.4 

3.854 

Hay  from  alkali  soil  .     .     . 

Tangl,  et  al. 

59-3 

3-7 

i.6i 

45-4 

3-803 

Hay  from  same,  irrigated  . 

Tangl,  et  al. 

50.4 

3-7 

2.0  ! 

43- 

3-741 

Alpine  hay  

Tangl,  et  al. 

50.1 

3-7 

i.6i 

44.6 

3.915 

Sour  meadow  hay      .     .     . 

Tangl,  et  al. 

66.4 

3-7 

I-51 

28.4 

3.607 

Silage  from  same  .... 

Tangl,  et  al. 

70.0 

3-7 

i.6l 

24-7 

3-352 

Average    

3-712 

Concentrates 

Oats   

Tangl,  et  al. 

41.4 

3.7 

O.2  1 

54-7 

4.493 

Distillery      residue      from 

grapes  and  beet  molasses 

Tangl,  et  al. 

66.9 

1.4 

o.8i 

30.9 

4-76i 

Average 

4.627 

Estimated. 


2  Not  corrected  to  N.  equilibrium. 


644  NUTRITION    OF    FARM    ANIMALS 

TABLE  1 88  — APPARENT  METABOLIZABLE  ENERGY  (Continued) 


PERCE 

NTAGE  LOS 

SES 

W 

wO 

PH        & 

AUTHOR 

In 
Feces 

In 
Urine 

In 

Meth- 
ane 

li 

CJ    O 

o  w 

Oil     W 

X 

METABOLIZABLE 
GRAM  DIGESTIBLI 
GANIC  MATTI 

HORSES 
Mixed  Rations 
Oats,  hay  and  straw 
Oats,  hay  and  straw       .     . 
Oats,  hay  and  straw       .     . 
Oats,  hay  and  straw       .     . 
Oats,  hay  and  straw       .     . 
Oats,  hay  and  straw       .     . 
Average    . 

Zuntz  and  Hagemann 
Zuntz  and  Hagemann 
Zuntz  and  Hagemann 
Zuntz  and  Hagemann 
Zuntz  and  Hagemann 
Zuntz  and  Hagemann 

% 

% 

% 

% 

% 

4-474 
3-236 
3-403 
3-803 
3-980 
5-052 
3  991 

SWINE 
Concentrates 
Millet      

Tangl,  et  al. 

28.8 

3-4 

0.2  1 

67.2 

4-335 

Pumpkins    
Barley    and   a   little    flesh 
meal     
Flesh  meal  
Wheat  gluten 

Tangl,  et  al. 

Fingerling,  et  al. 
Fingerling,  et  al. 
Fingerling,  et  al. 

25-6 

16.3 
6.9 
7-4 

3-9 

3-3 
8.9 
10.9 

I.41 

69.1 

80.4 

84.2 
81  7 

3-460 

4-521 
5-629 
4  908 

Starch     
Straw  pulp  
Sugar      

Fingerling,  et  al. 
Fingerling,  et  al. 
Fingerling,  et  al. 

2.6 

14.4 

2.7 

—      2.0 

-    1.8 

0.4 

- 

99-4 
87-4 
96.9 

4.076 
3-952 
3-75° 

Peanut  oil    
Barley,  dried  potatoes  and 
dried  yeast    
Same  +  palm  oil  .     .     .     . 
Same  +  dried  potatoes  .     . 
Computed  for  oil      ... 
Computed  for  dried  pota- 
toes 

Fingerling,  et  al. 

V.  d.  Heide  and  Klein 
V.  d.  Heide  and  Klein 
V.  d.  Heide  and  Klein 
V.  d.  Heide  and  Klein 

V  d  Heide  and  Klein 

-    0.4 

-    0.5 

- 

100.9 

8-997 

4-237 
4-442 
4.160 
9-552 

Whole  milk       
Skim  milk  and  saccharified 
starch       
Skim  milk  and  raw  starch  . 
Skim  milk  and  fat     ... 
Averages 

Flesh  meal  and  wheat 
gluten    
Whole  milk    .     .     .     . 
Peanut  oil      .... 
Other  rations      .     .     . 

GEESE 

Wellmann 

Wellmann 
Wellmann 
Wellmann 

Tangl  et  al 

4-7 

3-4 
3-8 
3-5 

9.8 

n-3 

10.5 
7-5 

g 

- 

85-5 

85.3 
85-7 
89.0 

76  i 

5467 

4.5I9 
3-825 
5-994 

5-269 

5-467 
8.997 
4-055 

3  753 

Millet      

DUCKS 
Millet 

Tangl,  et  al. 
Tangl  et  al 

4: 

.8 
i  6 

— 

56.2 
46  4 

2-723 

1  Estimated. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    645 

750.  Significance    of    metabolizable    energy.  —  By   metab- 
olizable  energy,  as    already  explained,  is    meant  simply  the 
energy  capable  of  transformation  in  the  body,  with  no  impli- 
cation as  to  the  proportion  of  the  energy  thus  transformed 
which  can  be  utilized  by  the  organism.     The  heat  evolved 
during  the  methane  fermentation,  for  example,  constitutes  part 
of  the  metabolizable  energy  as  thus  denned,  although  it  does 
not  enter  into  the  tissue  metabolism. 

The  metabolizable  energy  of  a  feeding  stuff  does  not  meas- 
ure its  production  value,  since  it  takes  account  of  only  one  of 
the  two  classes  of  losses  to  which  its  chemical  energy  is  sub- 
ject. Obviously,  however,  it  is  an  essential  factor  in  fixing 
that  value,  since  frequently  from  one-fourth  to  one-half  or  more 
of  the  feed  energy  is  thus  rejected  unused.  The  determination 
or  estimation  of  the  metabolizable  energy  of  a  feeding  stuff  is, 
therefore,  an  important  step  in  ascertaining  its  production 
value  as  regards  energy,  and  constitutes  an  advance  over  the 
simple  determination  of  digestibility,  since  it  takes  account  of 
the  losses  in  urine  and  methane  as  well  as  of  those  in  the  feces. 

751.  Real  and  apparent  metabolizable  energy.  —  The  metab- 
olizable energy  of  a  feeding  stuff  as  determined  experimentally 
in  the  manner  illustrated  in  a  preceding  paragraph  (747)  is  the 
aggregate  effect  as  regards  energy  of  all  the  influences  which  the 
feeding  stuff  exerts  on  the  digestive  processes. 

For  example,  in  one  of  Kellner's  experiments' beet  molasses 
added  to  a  basal  ration  diminished  the  amount  of  energy  car- 
ried off  in  the  methane  by  135.8  Cals.,  while  at  the  same  time 
it  so  depressed  the  digestibility  of  the  basal  ration  that  the 
amounts  lost  in  the  feces  and  urine  were  increased  by  1865.9 
Cals.  and  272.3  Cals.  respectively.  By  the  method  of  com- 
putation here  used,  the  algebraic  sum  of  these  amounts  is  vir- 
tually regarded  as  representing  the  losses  of  energy  from  the 
molasses  and  is  subtracted  from  the  gross  energy  of  the  latter 
to  obtain  its  metabolizable  energy.  The  metabolizable  energy 
as  thus  computed  expresses  the  net  increase  in  the  amount  of 
energy  available  for  conversion  in  the  body  and  may  be  called 
the  apparent  metabolizable  energy. 

On  the  other  hand,  the  results  for  the  metabolizable  energy 
of  the  digestible  nutrients  recorded  in  the  next  paragraph  in- 
clude corrections  for  these  secondary  effects.  They  aim  to  show 


646  NUTRITION    OF    FARM    ANIMALS 

the  actual  amounts  of  metabolizable  energy  supplied  by  the 
digested  portions  of  the  feed  irrespective  of  its  secondary  effects 
—  i.e.,  to  express  its  real  metabolizable  energy.  Such  figures 
give  a  more  accurate  idea  of  the  store  of  metabolizable  energy 
contained  in  the  feeding  stuff  regarded  by  itself,  while  the  ap- 
parent metabolizable  energy  is  better  adapted  for  use  in  a  dis- 
cussion of  questions  of  feeding.1  The  distinction  is  similar  to 
that  already  discussed  in  Chapter  III  (167)  between  real  and 
apparent  digestibility. 

752.  Computation  of  metabolizable  energy  from  digestible 
nutrients.  —  While,  in  the  absence  of  a  respiration  apparatus, 
the  metabolizable  energy  of  a  feeding  stuff  or  ration  may  be 
estimated  with  a  fair  degree  of  accuracy  by  the  method  out- 
lined in  previous  paragraphs,  not  every  experimenter  is  equipped 
to  determine  the  heats  of  combustion  of  the  feed  and  the  visible 
excreta,  and  no  satisfactory  method  of  computing  them  is  avail- 
able. Various  attempts  have  accordingly  been  made  to  compute 
the  metabolizable  energy  of  feeding  stuffs  from  chemical  data. 

One  such  method  is  that  employed  by  Rubner  and  by  At- 
water  for  estimating  the  metabolizable  energy  of  the  food  of 
man  and  of  carnivora  as  described  in  Chapter  VI  (324),  their 
factors  for  protein,  carbohydrates  and  fat  being  applied  directly 
to  the  digestible  nutrients  of  feeding  stuffs,  and  several  tables 
of  energy  values  as  thus  computed  have  been  published.  Later 
investigations,  however,  showed  that  the  results  thus  obtained 
were  much  too  high  in  the  case  of  herbivorous  animals,  es- 
pecially of  ruminants.  To  cite  but  a  single  instance,  experi- 
ments on  cattle  by  the  writer  2  gave  the  results  shown  in  Table 
189  for  metabolizable  energy  as  compared  with  those  computed 
by  the  use  of  Rubner's  factors,  and  Kellner's  somewhat  earlier 
results  3  led  to  the  same  general  conclusion. 

There  are  two  principal  reasons  for  this  discrepancy.  The 
first  is  the  extensive  fermentation  of  the  carbohydrates  in  the 
digestive  tract  of  ruminants,  leading  to  a  relatively  larger  loss 
of  energy  in  the  combustible  gases  excreted.  The  second  rea- 
son is  the  fact  that  the  urine  of  herbivora  carries  off  much 
more  non-nitrogenous  material  (224)  than  is  the  case  with  man 
or  carnivora.  The  results  of  direct  determinations  on  swine 

1  Compare  Armsby,  Principles  of  Animal  Nutrition,  pp.  291-293  and  333-335. 

2  Penna.  Expt.  Sta.,  Bui.  71,  p.  7. 

8  Landw.  Vers.  Stat.,  53  (1904),  440-449. 


THE  PRODUCTION  VALUES  OF   FEEDING  STUFFS    647 

show  much  smaller  differences  between  the  observed  and  com- 
puted results,  the  fermentation  losses  in  particular  being  notably 
less  with  swine  than  with  cattle  or  sheep  (745). 

TABLE  189.  —  COMPARISON  OF  METABOLIZABLE  ENERGY  PER  POUND 


COMPUTED  BY 
RUBNER'S 
FACTORS 

DIRECTLY 
DETERMINED 

Timothy  h«iy                         

Calories 

875 

Calories 

777 

QOI 

742 

Muizc  meal 

1^2^ 

1308 

Kellner  has  attempted  to  secure  factors  for  cattle  similar  to 
those  of  Rubner  for  men  and  carnivora  by  means  of  experiments 
in  which  approximately  pure  nutrients  (starch,  sugar,  oil,  gluten) 
were  added  to  a  basal  ration.  In  the  case  of  starch,  for  ex- 
ample, the  increase  in  the  amount  of  nitrogen-free  extract  di- 
gested was  compared  with  the  increase  in  the  total  metaboliz- 
able  energy  of  the  ration,  the  losses  of  energy  in  feces,  urine 
and  methane  being  determined  with  the  aid  of  a  respiration  ap- 
paratus by  the  method  of  indirect  calorimetry  (329).  The  re- 
sults are  corrected  for  the  effects  of  the  starch  upon  the  digest- 
ibility of  the  several  nutrients  of  the  basal  ration  and  upon 
the  losses  from  the  latter  in  urine  and  methane,  i.e.,  the  real 
metabolizable  energy  is  computed.  A  few  similar  de£ermina- 
tions  on  other  species  have  also  been  reported. 

In  an  earlier  publication 1  the  writer  has  discussed  in  con- 
siderable detail  the  recorded  experiments  regarding  the  metab- 
olizable energy  of  the  nutrients  digested  by  farm  animals 
with  the  results  summarized  in  the  following  table.  To  the 
extent  to  which  satisfactory  factors  can  be  selected,  this  table 
may  be  used  to  compute  the  metabolizable  energy  of  feeding 
stuffs  or  rations  whose  digestibility  is  known,  but  it  should  be 
noted  that  the  results  will  include  no  allowance  for  the  secondary 
effects  of  the  feed  on  the  digestive  processes  and  will  prob- 
ably be  higher  than  the  "  apparent "  metabolizable  energy 
obtained  by  direct  experiment. 

1  Principles  of  Animal  Nutrition,  pp.  302-335. 


648 


NUTRITION    OF    FARM    ANIMALS 


TABLE  190.  —  METABOLIZABLE  ENERGY  OF  DIGESTIBLE  NUTRIENTS  PER 

GRAM 


Protein  (N  X  6.25) : 

From  wheat  gluten      .     .  ' .     .     . 

From  wheat  gluten  (N  X  5.7)  .     . 

From  beet  molasses 

From  mixed  grain 

From  mixed  ration  of  oats,  hay 
and  straw 

From  meadow  riay 

From  timothy  hay 

From  straw 

Fat: 

From  peanut  oil 

From  hay  (ether  extract)  .  .  . 
Carbohydrates : 

Starch,  Kellner's  experiments    .     . 

Starch,  Kiihn's  experiments      .     . 

Nitrogen-free  extract  (assumed)     . 

Crude  fiber,  of  straw  pulp    .     .     . 

Crude  fiber,  of  hay  fed  alone     .     . 

Crude  fiber,  of  hay  added  to  basal 
ration 

Crude  fiber,  of  oat  straw       .     .     . 

Crude  fiber,  of  wheat  straw  .     .     . 

Crude  fiber,  of  mixed  ration      .     . 


CATTLE 


Cals. 
4.894 

3.984 


1.272 


8.821 
8.322 

3.648 

3.606 
3-3II 

3.606 

3-437 
3.001 


HORSE 


SWINE 


Cals.          j         Cals. 

—  — 


3.228 


4.185 


3-523 


4.083 


753.  Computation  of  metabolizable  energy  from  digestible 
organic  matter.  —  A  more  simple  and  direct  method  of  compu- 
tation may,  however,  be  employed,  based  on  the  total  digest- 
ible organic  matter  of  the  ration.  As  already  pointed  out, 
the  differences  shown  in  Table  188  between  the  percentages  of 
the  gross  energy  of  different  feeding  stuffs  which  are  metabo- 
lizable are  due  chiefly  to  differences  in  the  proportion  of  the 
chemical  energy  carried  off  in  the  feces,  while  the  losses  in  urine 
and  methane  are  far  more  uniform.  Accordingly,  the  metabo- 
lizable energy  per  unit  of  digestible  organic  matter  necessarily 
exhibits  much  smaller  variations  than  that  per  unit  of  dry 
matter,  and  in  fact  shows  a  striking  degree  of  uniformity. 
Selecting  those  averages  which  appear  most  trustworthy,  the 
results  may  be  summarized  as  follows :  — 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    649 


TABLE  191. —  METABOLIZABLE  ENERGY  PER  KILOGRAM  DIGESTIBLE  OR- 
GANIC MATTER 


NUMBER 
OF  SINGLE 
TRIALS 

MAXIMUM 

MINIMUM 

MEAN 

Roughage 
Cattle  .     .     
Sheep    
Horse    

73 
33 

12 

Therms 

3-74 
3-77 
3.Q2 

Therms 

3-31 
3-2Q 

•2.2C 

Therms 

3-53 
3-56 
•2.71 

Concentrates 
Cattle 

31 

4.8< 

3-70 

4  O4. 

Sheep    
Horse 

25 

8 

4.08 

A   76 

3-41 

4  40 

3-85 
462 

Swine  1       

36 

5-63 

3-46 

4.40 

A  similar  degree  of  uniformity  appears  when  the  results  on 
mixed  rations  are  compared,  as  the  following  summary  shows  :  — 

TABLE  192.  —  METABOLIZABLE  ENERGY  PER  KILOGRAM  DIGESTIBLE 
ORGANIC  MATTER  IN  MIXED  RATIONS 


NUMBER 
OF  SINGLE 
TRIALS 

MAXIMUM 

MINIMUM 

MEAN 

Therms 

Therms 

Therms 

Cattle 

Kellner  and  Kohler     .... 

38 

3-72 

3-48 

3.60 

Armsby  and  Fries 

26 

I  89 

•j  <l 

37-2 

Voltz,  etal  

4 

OI<JV 

4.12 

«jOA 

3.76 

•  /o 
3-98 

Tangl  et  al 

8 

41  1 
.  A  ±. 

•2    64. 

^  8=; 

All  experiments 

76 

41  2 
•  x  * 

J-V+ 

2  4.8 

O'UO 

^  67 

Sheep 

/  u 

O'T-0 

O'"/ 

Tangl  et  al  

16 

4.^0 

^.CQ 

2  70 

Voltz,  et  al  . 

12. 

T-'O 

4.05 

O  0 

3.15 

O    I  V 

3-79 

All  experiments  

35 

4-30 

3-15 

3-79 

Horse 

Lehmann,    Zuntz    and    Hage- 

mann 

6 

4.47 

2.24 

2.QQ 

Tangl,  etal  

8 

T**T"  / 
4.31 

OH" 
4-19 

o  yy 

4-25 

All  experiments  

14 

4-43 

3-48 

4.06 

Excluding  feeds  containing  much  oil. 


650 


NUTRITION  OF  FARM   ANIMALS 


Feeding  stuffs,  rich  in  protein  and  fat,  especially  the  latter, 
naturally  give  higher  values,  as  is  illustrated  by  the  following 
results,  likewise  taken  from  Table  188. 

TABLE  193.  —  METABOLIZABLE  ENERGY  PER  KILOGRAM  DIGESTIBLE 

ORGANIC  MATTER 
Palmnut  meal 

Cattle 4-85  Therms 

Sheep 3.98  Therms 

Wheat  gluten 

Cattle 4.79  Therms 

Flesh  meal 

Swine 5.63  Therms 

Taking  the  pound  as  the  unit  for  reasons  of  practical  con- 
venience, it  is  believed  that  for  the  approximate  computation 
of  the  metabolizable  energy  of  ordinary  feeding  stuffs  or  ra- 
tions whose  content  of  digestible  organic  matter  is  known  or 
can  be  estimated,  the  following  factors  may  be  used,  at  least  for 
ruminants,  without  serious  error :  — 

TABLE  194.  —  METABOLIZABLE    ENERGY    PER    POUND    DIGESTIBLE    OR- 
GANIC MATTER 


RUMINANTS 

SWINE 

HORSES 

Roughage      

Therms 
1.588 

Therms 

Therms 
1.683 

Mixed  rations  —  roughage  and  concentrates 

— 

1.810 

Concentrates 

Grains  and  similar  material 
With  less  than  5  per  cent  digestible  fat   . 
With  more  than  5  per  cent  digestible  fat  . 
Oil  meals  and  materials  high  in  protein 

1.769! 
1.814  J 

1.996-2.177 

1-935 
2.390 

2.096 

Losses  of  energy  in  heat  production 

It  was  stated  in  a  previous  paragraph  (741)  that  the  gross 
energy  of  a  feeding  stuff  is  subject  to  two  classes  of  losses,  viz., 
losses  of  untransformed  chemical  energy  in  the  excreta  and 
losses  through  conversion  into  heat.  The  losses  of  chemical 
energy  have  been  discussed  in  the  preceding  paragraphs.  The 
second  class  of  losses  has  now  to  be  considered. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    651 

754.  Influence  of  feed  consumption  on  metabolism.  —  As 

is  evident  from  §  i  of  Chapter  VIII  (365),  the  fact  that  the 
consumption  of  feed  tends  to  increase  the  heat  production  of  an 
animal  has  become  a  commonplace  of  physiology.  The  mag- 
nitude of  the  effect  varies  within  rather  wide  limits  according 
to  the  species  of  animal  and  the  chemical  and  physical  proper- 
ties of  the  feed,  while  there  is  still  more  or  less  difference  of 
opinion  as  to  its  causes.  Zuntz  and  his  associates  have  called 
it  "  work  of  digestion  "  and  have  attributed  it  largely  to  in- 
creased muscular  and  glandular  activity  of  the  digestive  and 
excretory  organs.  Numerous  investigations  in  this  field  have 
been  made  on  carnivora  or  on  man,  in  which  the  increase  of 
the  metabolism  is  not  usually  very  large  except  when  much  pro- 
tein is  consumed.  The  more  recent  experiments  on  these  species 
appear  to  have  shown  that  the  mechanical  work  of  the  digestive 
organs  is  but  a  small  factor  and  that  the  term  "  work  of  di- 
gestion "  is  not  a  fortunate  one.  With  herbivora  and  especially 
with  ruminants,  on  the  other  hand,  the  total  effect  on  the  heat 
production  is  quantitatively  much  more  marked,  and  the 
mechanical  factor  is  of  greater  significance. 

755.  Results  on  cattle.  —  As  illustrated  in  an  earlier  chapter 
(364,  449)  the  effect  of  feed  consumption  upon  the  metabolism 
of  ruminants  may  be  determined  by  comparing  two  periods  in 
which  different  amounts  of  the  same  feeding  stuff  or  ration  are 
consumed,  the  increment  of  heat  production  on  the  heavier 
ration  being  compared  with  the  additional  amount  of  feed  con- 
sumed.    The  experiments  thus  far  reported  have  been  almost 
exclusively  upon  cattle,  the  principal  ones  being  the  pioneer 
investigations  of  Kellner  and  Kohler  1  and  the  later  ones  of 
Armsby  and  Fries.2 

Most  of  Kellner  and  Kohler's  experiments  were  made  on  super- 
maintenance  rations.  The  heat  production  was  not  measured  directly, 
but  computed  from  the  balance  of  carbon  and  nitrogen  in  the 
manner  indicated  in  Chapter  VI  (329),  i.e.,  by  indirect  calorimetry. 
Only  a  few  of  their  results  have  as  yet  been  published  in  full,  but 
from  data  regarding  a  few  of  the  oth<y:  experiments  contained  in 
Kellner's  book,  the  increments  of  heat  production  may  be  computed. 


.  Vers.  Stat.,  47  (1896),  275;  50  (1898),  245;  53    (1900),    1-474.     Die 
Ernahrung  der  landwirtschaftlichen  Nutztiere,  6th  Ed.,  Berlin,  1912. 
2  Jour.  Agr.  Research,  3  (1915),  435. 


652 


NUTRITION  OF  FARM   ANIMALS 


Armsby  and  Fries'  experiments  included  both  submaintenance  and 
supermaintenance  rations  and  the  heat  was  measured  directly  with  a 
respiration  calorimeter. 

As  elsewhere  summarized  by  the  writer,  the  average  results 
derived  from  the  two  series  of  experiments  are  as  follows :  — 

TABLE  195.  —  INCREMENT  OF  HEAT  PRODUCTION  BY  CATTLE 


EXPERI- 
MENTERS 1 

HEAT  INCRE- 
MENT PER   100 
LB.  DRY 
MATTER  EATEN 

Roughage 
Timothy  hay  

A  &  F 

Therms 

•2  C   4.7 

Red  clover  hay    

A  &  F 

44-  1  3 

Red  clover  hay 

K  &  K 

4.2  27 

Mixed  hay      

A  &  F 

4-4-  4.1? 

Alfalfa  hay      

A  &  F 

C?    O3 

'  '  Grass  hay  '  ' 

K  &  K 

4.7  4.O 

Meadow  hay  ... 

K&  K 

56  88 

Rowen   

K  &  K 

4?    46 

M^aize  stover 

A  &  F 

4.8  31 

Barley  straw  . 

K  &  K 

30  78 

Oat  straw  

K  &  K 

46.00 

W^heat  straw 

K  &  K 

51  62 

Straw  pulp      

K  &  K 

52  62 

Concentrates 
M^aize  meal 

A  &  F 

e8  33 

Hominy  feed 

A  &  F 

6l  Q2 

Wheat  bran    
Grain  mixture  No   i  ^ 

A&F 
A  &  F 

53-39 
60  10 

Grain  mixture  No   2  ••*                                           . 

A&F 

^1.76 

Cottonseed  meal      
Linseed  me*al 

K&K 
K  &  K 

44-36 
CA  70 

Palmnut  meal      .     .          

K&K 

45.68 

Peanut  meal   

K&K 

52.57 

Beet  molasses 

K&K 

'  44  82 

Starch    

K&K 

56.61 

Peanut  oil  

K&K 

78.34 

Wheat  gluten 

K&K 

CK.oS 

1  In  this  and  following  tables,  A&F  signifies  Armsby  and  Fries  and  K&K 
Kellner  and  Kohler. 

2  Wheat  bran,  14.28  per  cent;    corn  meal,  42.86  per  cent;    old  process  linseed 
meal,  42.86  per  cent. 

3  Corn  meal,  60  per  cent ;   crushed  oats,  30  per  cent ;   old  process  linseed  meal, 
10  per  cent. 


THE   PRODUCTION  VALUES  OF  FEEDING  STUFFS    653 


756.  Results  on  sheep.  —  In  a  series  of  respiration  experi- 
ments upon  two  sheep  by  Kern  and  Wattenberg,  reported  by 
Henneberg  and  Pfeiffer,1  varying  amounts  of  nearly  pure  pro- 
tein in  the  form  of  conglutin  or  of  flesh  meal  were  added  to  a 
basal  ration  of  hay  and  barley  meal.  The  writer2  has  com- 
puted from  the  recorded  results  of  these  experiments  the  metab- 
olizable  energy  of  the  additions  to  the  basal  ration  and  the 
energy  of  the  resulting  gain.  The  difference  between  the.  two 
shows  the  amount  of'  energy  lost  as  heat. 

TABLE  196. — INCREMENT  OF' HEAT  PRODUCTION  BY  SHEEP 


HEAT  INCREMENT 

DRY 

METABO- 

PERIOD 

MATTER 
or 
ADDED 
FEED 

ENERGY 

OF 

ADDED 
FEED 

OF  RE- 
SULTING 
GAIN 

Total 

Per  100 
Lb.  Dry 
Matter 
Eaten 

Grams 

Cals. 

Cals. 

Cals. 

Therms 

f 

II 

117.6 

588.4 

517.8 

70.6 

27.24 

Conglutin     ...     y 

III 

234-8 

1100.3 

741.8 

358.5 

69.26 

IV 

350.8 

1639.2 

1106.9 

532-4 

68.86 

Flesh-meal  .    .    .     < 

V 
VI 

258.0 
63.5 

1131.7 
454-9 

672.5 
315.7 

459-2 
139.2 

69.31 
49.71 

The  results  are  notably  lower  than  those  obtained  by  Kellner 
for  wheat  gluten  fed  to  cattle,  although  in  the  three  middle 
periods  they  are  higher  than  those  found  with  that  species  for 
other  concentrates,  but  there  are  several  points  of  uncertainty 
in  the  experimental  results  and  the  method  of  computation  is 
an  approximate  one.  On  the  whole,  pending  further  investi- 
gation, it  appears  probable  that  the  results  obtained  with  cattle 
may,  without  very  serious  error,  be  regarded  as  applicable  to 
other  species  of  ruminants. 

757.  Results  on  swine.  —  The  data  regarding  the  increment 
of  heat  production  consequent  on  the  consumption  of  feed  by 
swine,  although  more  abundant  than  those  for  sheep,  are  still 
rather  meager.  Respiration  experiments  made  by  Meissl, 
Strohmer  and  Lorenz 3  in  a  study  of  the  sources  of  animal  fat, 

1  Jour.  Landw.,  38  (1890),  215.       2  Principles  of  Animal  Nutrition,  pp.  463-465. 
'Ztschr.  Biol.,  22  (1886),  63. 


654  NUTRITION    OF    FARM    ANIMALS 

and  by  Kornauth  and  Arche 1  upon  the  nutritive  value  of 
cockle  may  be  made  the  basis  of  estimates  of  the  energy  expendi- 
ture due  to  feed  consumption,  while  the  later  investigations 
of  Von  der  Heide  and  Klein,2  of  Fingerling,  Kohler  and  Rein- 
hardt3  and  of  Wellmann,4  were  directed  more  specifically 
toward  a  study  of  the  energy  relations. 

Neither  of  the  two  investigations  first  mentioned  included  any 
energy  determinations,  but  by  substantially  the  same  method  as  that 
applied  in  the  previous  paragraph  to  experiments  with  sheep,  assum- 
ing an  average  maintenance  requirement,  the  heat  increment  per 
unit  of  feed  may  be  computed. 

Von  der  Heide  and  Klein,  in  Zuntz's  laboratory,  have  measured  with 
the  aid  of  a  respiration  apparatus  of  the  Regnault-Reiset  type  (298) 
the  metabolism  of  three  swine  on  a  basal  ration  slightly  more  than 
sufficient  for  maintenance  and  consisting  of  barley  meal,  dried  potatoes 
and  dried  yeast,  and  also  the  effect  of  the  addition  to  this  basal  ration 
of  dried  potatoes  and  of  palm  oil.  The  energy  of  the  feed  and  excreta 
was  determined.  Estimating  the  fasting  katabolism  of  the  three  ani- 
mals from  the  body  surface,  the  results  may  be  computed  as  in  the 
two  previous  experiments.  A  computation  from  the  total  heat  in- 
crements above  the  basal  ration  (i.e.,  without  correction  for  the  dif- 
ferences in  live  weight)  gives  somewhat  higher  results. 

Fingerling,  Kohler  and  Reinhardt,  in  experiments  on  two  growing 
swine  about  eight  months  old,  added  approximately  pure  nutrients 
(starch,  peanut  oil,  straw  pulp,  wheat  gluten,  flesh  meal  and  sugar) 
to  a  basal  ration  consisting  of  ground  barley  with  a  little  flesh  meal. 
The  animals  gained  steadily  in  weight.  By  a  comparison  of  the  first 
and  last  periods,  on  the  basal  ration,  the  authors  compute  the 
average  fasting  katabolism  per  square  meter  of  body  surface  to 
have  been  1044.67  Cals.,  which  agrees  fairly  well  with  the  average 
computed  in  Chapter  VIII  (377),  viz.,  1089  Cals.  per  square 
meter.  Taking  the  average  of  the  first  and  last  periods  as  the  basal 
ration,  in  order  to  eliminate  the  effects  of  the  increase  in  live  weight, 
and  subtracting  it  from  the  results  of  the  intermediate  periods,  the 
fasting  katabolism  being  estimated  in  proportion  to  the  surface  of 
the  animal,  the  heat  increment  due  to  the  added  nutrients  may  be 
computed  in  the  manner  illustrated  for  starch  in  the  following  table, 
while  by  correcting  the  results  obtained  in  the  first  and  last  periods  for 
the  small  amount  of  flesh  meal  included  in  the  ration,  the  energy  expen- 
diture per  gram  of  dry  matter  in  the  barley  may  likewise  be  estimated. 

1  Landw.  Vers.  Stat.,  40  (1892),  177.  2  Biochem.  Ztschr.,  55  (1913),  195. 

3  Landw.  Vers.  Stat.,  84  (1914),  149.  4  Landw.  Jahrb.,  46  (1914),  499. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    655 


TABLE  197.  —  EXAMPLE  OF  COMPUTATION  OF  HEAT  INCREMENT  IN 

SWINE 


HEAT 

TOTAL 

METAB- 

COM- 

ESTI- 

INCREMENT 

STARCH 

MATTER 
CON- 
SUMED 

OLIZA- 
BLE 

ENERGY 

GAIN  BY 
ANIMAL 

HEAT 
PRODUC- 
TION 

FASTING 
KATAB- 

OLISM 

Total 

Per 
Gram 
Dry 

Matter 

Grams 

Cals. 

Cals. 

Cals. 

Cals 

Cals. 

Cals. 

Pig  3 

Period  2      

1582.2 

5990.32 

2508.19 

3482  13 

2  2OO  71 

Average  of  periods  i  and  6 

1180.3 

4368.40 

1041.03 

3327-37 

2328.68 

998.69 

0.846 

Starch  by  difference      .     . 

401.9 

1621.92 

1467.16 

154-76 

—  127.97 

282.73 

0.704 

Wellmann,  in  the  course  of  experiments  on  the  rearing  of  calves 
and  pigs  on  skim  milk  and  modified  skim  milk,  determined  by  means 
of  comparative  slaughter  tests  the  gain  of  flesh  and  fat  by  two  pigs 
during  twenty-three  and  thirty-four  days  respectively,  and  also  col- 
lected the  feces  and  urine  quantitatively  during  the  entire  period  of 
feeding.  The  energy  of  the  feed  and  excreta  was  determined  directly. 
Assuming  a  basal  katabolism  of  noo  Cals.  per  square  meter  of 
surface  (377),  the  heat  increment  due  to  the  feed  may  be  computed 
as  in  previous  cases. 

The  results  of  the  foregoing  investigations  are  summarized 
in  Table  198.  One  of  Wellmann's  results,  obtained  with  a 
very  restless  animal,  may  be  regarded  as  probably  too  high  and 
has  been  excluded.  In  Von  der  Heide  and  Klein's  experiment 
on  palm  oil  the  quantity  of  fat  consumed  was  relatively  large 
as  compared  with  that  in  Fingerling's  experiment  on  peanut 
oil,  although  the  total  ration  was  not  excessive. 

Despite  some  irregularities,  a  comparison  of  these  results 
with  those  for  cattle  (755)  shows  clearly  that  with  swine  the 
energy  expenditure  consequent  on  feed  consumption  is  de- 
cidedly less  than  with  ruminants.  Fingerling's  results  with 
approximately  pure  nutrients  are  especially  interesting  in  this 
respect.  As  regards  the  more  soluble  carbohydrates  (starch 
and  sugar)  one  can  hardly  err  in  ascribing  the  difference  largely 
to  the  fact  that  in  the  comparatively  simple  digestive  organs 
of  swine  fermentations  occur  only  to  a  limited  extent,  while  in 
cattle  they  have  been  estimated  to  account  for  from  9  to  16  per 


656 


NUTRITION    OF    FARM    ANIMALS 


cent  of  the  total  increment  in  heat  production.  Straw  pulp,  on 
the  contrary,  caused  fully  as  great  an  increase  in  the  heat  pro- 
duction of  swine  as  in  that  of  cattle.  Fingerling  explains  this 
upon  the  supposition  that  the  straw  pulp  was  fermented  rather 
than  digested.  He  failed,  however,  to  find  any  corresponding 
excretion  of  methane  (745),  and  Von  der  Heide,  Steuber  and 
Zuntz 1  have  observed  only  a  relatively  small  evolution  of  com- 
bustible gases  from  this  material  in  case  of  the  horse.  The 
differences  as  regards  oil  and  protein  are  not  readily  explicable 
since,  according  to  Kellner,  they  are  not  subject  to  the  methane 
fermentation. 

TABLE  198.  — •  INCREMENT  OF  HEAT  PRODUCTION  BY  SWINE 


' 

EXPERIMENTER 

HEAT  IN- 
CREMENT 

PER    100 
LB.   DRY 

MATTER 
EATEN 

Grains 
Rice               .     . 

M^eissl  et  al 

Therms 

[32.0 
)  AI  -i 

Barley           ... 

M^eissl  et  al 

\  41->5 
[36.7 

29  6 

Barley      

Fingerling  et  al 

AC    2 

Dried  potatoes       
Flesh  meal    

Mixed  rations 

Rice,  flesh  meal  and  whey  
Cockle,  barley  and  maize    
Rape  cake,  barley  and  maize  .... 
Skim  milk  and  flour  . 

V.  d.  Heide  and  Klein 

Fingerling,  et  al. 

Meissl,  et  al. 
Kornauth  and  Arche 
Kornauth  and  Arche 
\Vellmann 

49.76 
47.90 

41.1 
24.4 
27.9 

60  9 

Single  nutrients 
Starch      .         .     . 

Fingerling  et  al 

51    Q-J 

Cane  sugar   
Straw  pulp   
Wheat  gluten    
Peanut  oil     
Palm  oil 

Fingerling,  et  al. 
Fingerling,  et  al. 
Fingerling,  et  al. 
Fingerling,  et  al. 
V  d  Heide  and  Klein 

47.22 
60.56 
SI-67 
30.35 

IOC  02 

1  Biochem.  Ztschr.,  74  (1916),  161. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    657 


758.  Experiments  on  the  horse.  —  No  experiments  on  this 
animal  have  been  reported  in  which  the  energy  expenditure  due 
to  the  consumption  of  a  single  feeding  stuff  has  been  deter- 
mined.    Practically  the  only  data  available  are  those  derived 
from  the  extensive  investigations  of  Zuntz  and  Hagemann,  the 
results  of  which  regarding  the  fasting  katabolism  have  been 
considered  in  Chapter  VIII  (385).     On  the  basis  of  their  ex- 
periments they  compute  the  energy  expenditure  and  the  net 
energy  value  from  the  composition    and    digestibility  of   the 
ration  by  a  method  identical  in  principle  with  that  employed 
in  the  experiments  on  cattle  already  described.     The  experi- 
ments were  conducted   so  differently,  however,  as  to  consti- 
tute practically  a  distinct    method  and    they   may  be    more 
conveniently  considered  in  connection  with  the  computation  of 
net  energy  values  discussed  in  subsequent  paragraphs  (775-778) . 

759.  Results  on  carnivora.  —  Mention  was  made  in  Chapter  VIII 
(365,  366)  of  the  fact  that  in  carnivora,  as  well  as  in  herbivora  and 
omnivora,  the  consumption  of  feed  stimulates  the  heat  production, 
the  increase  having  been  called  by  Rubner    the  specific  dynamic 
action.    It  is  evident  that  experiments  like  those  of  Rubner  and 
of  Lusk  were  virtually  determinations  of  net  energy  values  for  these 
species.    While  having  no  direct  bearing  on  the  question  of  the  nutri- 
tive values  of  feeding  stuffs  for  farm  animals,  these  data  have  been 
extensively  quoted  in  related  physiological  writings  and  it  seems  de- 
sirable to  include  them  here.     Rubner's  later  experiments  were  made 
at  about  33°  C.,  or  considerably  above  the  critical  temperature  for 
the  dog,  a  fact  which  is  of  importance  in  the  interpretation  of  the 
results  (395-397). 

A  balance  experiment  with  a  respiration  calorimeter  in  which 
nearly  enough  fat  was  fed  to  supply  the  requirement  for  energy  gave 

TABLE  199.  —  INCREMENT  OF  HEAT  PRODUCTION  BY  DOG  ON  FAT  DIET 


METABOLIZABLE 
ENERGY  OF 
FEED 

GAIN  BY  BODY 

HEAT  PRODUC- 
TION 

Fat  fed  

Cals. 

C-2    A 

Cals. 

—     7  r 

Cals. 
60  9 

Fasting 

Q 

—  <A  O 

CA    o 

Difference 

£  5     A 

Af\  e 

6  o 

Percentages     

100.00 

87.08 

vj.y 
12.92 

2  U 


658 


NUTRITION    OF    FARM    ANIMALS 


per  kilogram  live  weight  the  results  shown  in  Table  199,  which  are 
stated  in  a  form  somewhat  different  from  that  used  by  Rubner  but 
which  in  substance  are  identical  with  his. 

These  figures-  appear  somewhat  remarkable  in  view  of  the  fact 
that  the  comparison  is  virtually  with  body  fat.  Literally  inter- 
preted, it  means  that  the  energy  of  feed  fat  is  only  87  per  cent  as 
valuable  for  maintenance  as  the  energy  of  mobilized  body  fat  plus  a 
little  protein.  If  this  be  true,  it  implies  a  larger  expenditure  of 
energy  in  the  digestion  of  fat  or  a  greater  stimulating  effect  of  the 
resorbed  fat  upon  cell  activity  than  now  seems  probable,  since  the 
katabolism  of  resorbed  feed  fat  can  hardly  differ  greatly  from  that  of 
body  fat.  Rubner's  figure  is  the  result  of  a  single  experiment  and 
unfortunately  it  enters  into  the  computation  of  all  the  other  results. 
It  is  a  matter  of  much  interest,  therefore,  that  Lusk  1  has  found  a 
much  lower  heat  increment  for  fat.  In  two  calorimetric  experiments 
in  which  an  emulsion  of  olive  oil  was  given  to  a  dog  he  found  the 
additional  heat  elimination  to  be  0.92  per  cent  and  1.49  per  cent 
of  the  energy  of  the  oil,  so  that  on  the  average  98.8  per  cent  of  energy 
of  the  fat  was  available  for  maintenance,  a  much  higher  figure  than 
Rubner's. 

Both  Rubner  and  Lusk  find  the  most  marked  effect  to  be  produced 
by  protein.  In  two  other  experiments  by  Rubner  an  amount  of  lean 
meat  nearly  sufficient  to  maintain  the  dog  was  fed.  The  meat  con- 
tained a  small  amount  of  fat,  the  average  metabolizable  energy  of 
the  feed  per  kilogram  live  weight  being  as  follows :  — 

In  protein  56.70  Cals. 

In  fat  4.95  Cals. 

61.65  Cals. 

Using  the  data  afforded  by  the  experiment  on  fat,  the  heat  incre- 
ment due  to  the  protein  may  be  computed  as  follows :  — 

TABLE  200.  —  INCREMENT  or  HEAT  PRODUCTION  BY  DOG  ON  MEAT  DIET 


METABOLIZABLE 
ENERGY  OF 
FEED 

GAIN  BY  BODY 

HEAT  PRODUC- 
TION 

Meat  fed  
Fasting  

61.65  Cals. 
o 

-    8.90  Cals. 
-51.50  Gals. 

70.55  Cals. 
51.50  Cals. 

Difference  
Difference  due  to  fat  .  . 

61.65  Cals. 
4.95  Cals. 

42.60  Cals. 
4.31  Cals. 

19.05  Cals. 
0.64  Cals. 

Difference  due  to  protein  . 
Percentages  

56.70  Cals. 
100.00 

38.29  Cals. 
67.53 

18.41  Cals. 
32-47 

Jour.  Biol.  Chem.,  13  (1912),  38. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS     659 


Williams,  Riche  and  Lusk  report  results  agreeing  substantially 
with  those  of  Rubner  when  computed  in  the  same  way,  although 
they  regard  his  method  of  computation  as  erroneous.  Rubner's 
and  Lusk's  averages  are  contained  in  the  following  table.  It 
should  be  clearly  understood  that  these  figures  are  not  applicable 
to  the  "  digestible  nutrients  "  of  the  feed  of  herbivora. 

TABLE  201.  —  PERCENTAGE  OF  METABOLIZABLE  ENERGY  AVAILABLE 
Average  Results  for  Dogs 


RUB 

NER 

Lu 

SHE 

Increment    of 
Heat  Pro- 
duction 

Available  for 
Maintenance 

Increment    of 
Heat  Pro- 
duction 

Available  for 
Maintenance 

Body  protein    .... 

31-9 

68.1 





Meat  protein    .... 

30.9 

69.1 

36.0 

64.0 

Gelatin    

28.0 

72.0 

— 

— 

Fat 

12  7 

87  3 

I  2 

08  o 

Cane  sugar  .     .     .     .     . 

5-8 

94-2 

Dextrose      

4-9 

95-i 

Net  energy  values 

In  the  previous  paragraphs  there  have  been  considered  the 
losses  of  energy  in  the  excreta  and  those  due  to  the  increased 
heat  production  which  results  from  the  consumption  of  feed. 
As  pointed  out  in  the  introductory  paragraphs  of  this  section, 
that  portion  of  the  gross  energy  of  a  feeding  stuff  which  re- 
mains after  deducting  these  two  classes  of  losses  constitutes  its 
net  energy  value,  or  its  production  value  as  regards  energy. 
Stated  in  a  slightly  different  way,  the  net  energy  value  is  equal 
to  the  metabolizable  energy  minus  the  increment  of  heat  pro- 
duction. It  differs  from  the  relative  value,  based  on  the  di- 
gestible nutrients  or  the  metabolizable  energy,  in  taking  ac- 
count of  all  the  losses  of  energy  to  which  the  feed  is  subject. 

760.  Net  energy  values  for  cattle.  —  It  is  apparent  from  the 
foregoing  discussions  that  the  data  regarding  losses  of  energy 
and  net  energy  values  are  much  more  abundant  for  cattle 
than  for  any  other  species  of  farm  animals.  Combining  the 


66o 


NUTRITION    OF    FARM    ANIMALS 


data  of  Table  195  (755)  regarding  the  losses  due  to  increased 
heat  production  with  those  regarding  the  losses  of  chemical 
energy  in  the  excreta  recorded  in  another  form  in  Table  188 
(749)  gives  the  results  contained  in  the  following  tables,1  the 

TABLE  202.  —  NET  ENERGY  VALUES  or  FEEDING  STUFFS  FOR  RUMINANTS 
Per  Hundred  Pounds  of  Dry  Matter 


EXPERI- 
MENTERS 

GROSS 
ENERGY 

LOSSES 
or 
CHEM- 
ICAL 
ENERGY 
IN  EX- 
CRETA 

METABO- 

LIZABLE 

ENERGY 

INCRE- 
MENT or 
HEAT 
PRO- 
DUC- 
TION 

NET 
ENERGY 
VALUES 

Therms 

Therms 

Therms 

Therms 

Therms 

Roughage 

Timothy  hay     .... 

A&F 

204.94 

120.84 

84.10 

35-47 

48.63 

Red  clover  hay  .... 

A&F 

202.40 

111.63 

90.77 

44-13 

46.64 

Red  clover  hay  .... 

K&K 

— 

— 

42.27 

36.79 

Mixed  hay    

A&F 

199.27 

112.45 

86.82 

44-45 

43-37 

Alfalfa  hay    . 

\  &  F 

0 

111.18 

87  13 

C  7   D7 

"Grass  hay"     .... 

K&K 

-1 

°  /  •  L  o 

47-40 

36.43 

Meadow  hay      .... 

K&K 

201.08 

102.51 

98.57 

56.88 

41.69 

Rowen 

K&K 





77   3/12 

/i6 

33  88 

Maize  stover 

\  &  F 

6 

107.96 

88^4 

8    i 

oo-00 

Barley  straw      .... 

K&K 

— 

73-672 

39-78 

33-89 

Oat  straw 

K&K 

2OI  .  2  2 

T  ?C\   TO 

79  O2 

4.6  OO 

Wheat  straw      .... 

K&K 

201.58 

138.89 

62.69 

51.62 

11.07 

Straw  pulp    

K&K 

i88.n 

I42.l6 

c;2  62 

80  <A. 

Concentrates 

0  ^  •  v  * 

Maize  meal   .... 

A&F 

2O  I  A.Q 

g 

z 

g 

2  <8 

Hominy  feed     .... 

A&F 

A\J±  -^f  V 

213.60 

53-84 

159-76 

61.92 

97.84 

Wheat  bran  . 

A&F 

2O£  C7 

01  67 

1  1  3..QO 

C2    7O 

Grain  mixture  No.  i  .     . 

A&F 

^O  O  / 
212.51 

y  A.U  / 

73-53 

138.98 

60.19 

78.79 

Grain  mixture  No.  2  .     . 

A&F 

2O9.06 

73.48 

135-58 

5L76 

83.82 

Cottonseed  meal    .     .     . 

K&K 



— 

129.15  2 

44-36 

84.79 

Linseed  meal     .... 

K&K 

. 

— 

137.72  2 

54-79 

82.93 

Palmnut  meal    .... 

K&K 



— 

124.57  2 

45-68 

78.89 

Peanut  meal 

K&K 



134.13  2 

^       C7 

gj  1-5 

Beet  molasses    .... 

K&K 

169.80 

42.88 

126.92 

44.82 

82.10 

Starch       

K&K 

188.35 

49-95 

138.40 

56.61 

81.89 

Peanut  oil 

K&K 

429.OO 

no       ^ 

nc 

^0 

161.71 

Wheat  gluten     .... 

K&K 

253-10 

89.58 

163-52 

95.08 

68.45 

Penna.  Expt.  Sta.,  Bui.  142. 


2  Estimated  from  digestible  organic  matter. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    66 1 


first  showing  the  losses  of  energy  and  the  net  energy  values  per 
100  pounds  of  dry  matter  and  the  second  the  percentage  dis- 
tribution of  the  gross  energy  of  the  feeding  stuffs  between 
the  various  losses  and  the  net  energy  values.  As  already  in- 
dicated (745,  749,  756),  it  appears  probable  that  these  values 
may  be  used  also  for  other  classes  of  ruminants  without  serious 
error. 

TABLE  203.  —  DISTRIBUTION  OF  ENERGY  OF  FEED  IN  RUMINANTS 


EXPERI- 
MENTERS 

REJECTED 
UNUSED  IN 
EXCRETA 

INCREMENT 
OF  HEAT 
PRODUC- 
TION 

NET 
ENERGY 
VALUE 

Roughage 

% 

% 

% 

Timothy  hay 

A.  &  F 

17 

2/1 

Clover  hay 

A&F 

r  r 

A  / 
22 

ZH- 
2"? 

Mixed  hay          .     . 

A&F 

v)O 

22 

zo 
21 

Alfalfa  hay    

A&F 

56 

27 

17 

M^eadow  hay 

K  &  K 

rj 

28 

21 

Maize  stover      

A&F 

Dx 

55 

25 

2O 

Oat  straw       !     

K&K 

64 

23 

13 

Wheat  straw       

K&K 

69 

26 

5 

Extracted  straw      

K&K 

24 

28 

48 

Concentrates 

Maize  meal    .     .     .     .     .     .     . 

A&F 

2O 

A6 

Hominy  feed      

A&F 

25 

V 

29 

t^\J 

46 

Wheat  bran   . 

A&F 

Af 

26 

20 

Grain  mixture  No.  i   .     .     .     . 

A&F 

H-O 

35 

28 

*y 

37 

Grain  mixture  No.  2   .... 

A&F 

35 

25 

40 

Beet  molasses     

K&K 

25 

26 

49 

Starch 

K&K 

27 

20 

Peanut  oil 

K&K 

*  I 

A  A 

ou 

18 

g 

Wheat  gluten     

K&K 

trr 

35 

38 

27 

761.  Net  energy  values  for  swine.  —  Combining  in  the  same 
form  the  results  of  the  determinations  of  the  heat  increment 
caused  by  the  consumption  of  feed  by  swine  (757)  which  are 
recorded  in  Table  198  and  such  data  regarding  the  losses  of 
energy  in  feces,  urine  and  methane  as  are  contained  in  Table  188 
(749)  yields  the  net  energy  values  shown  in  Table  204 :  — 


662 


NUTRITION    OF    FARM    ANIMALS 


TABLE   204.  —  NET  ENERGY  VALUES  OF  FEEDING  STUFFS  FOR  SWINE 
Per  100  Pounds  Dry  Matter 


EXPERIMENTERS 

GROSS 

EN- 
ERGY 

LOSSES 

OF 

CHEM- 
ICAL 
ENERGY 
IN  EX- 
CRETA 

METAB- 

OLIZA- 
BLE 

ENERGY 

INCRE- 
MENT 

OF 

HEAT 
PRO- 
DUC- 
TION 

NET 
ENERGY 
VALUES 

Therms 

Therms 

Therms 

Therms 

Therms 

Grains 

Rice   

Meissl,  et  al. 

2/S    *7 

TC8  7 

Barley     

Meissl,  et  al. 





I5L5 

O        / 

29.6 

100</ 
I2I.9 

Barley     

Fingerling,  et  al. 

206.9 

41.1 

165.8 

45-3 

I2O-5 

Dried  potatoes     .     . 

V.  d.  Heide  and 

Klein 

— 

— 

151.1 

49-8 

IOI.3 

Flesh  meal  .... 

Fingerling,  et  al. 

282.6 

44-5 

238.1 

47-9 

I9O.2 

Mixed  Rations 

Rice,  flesh  meal  and 

whey  

Meissl,  et  al. 

— 

— 

190.7 

41.1 

149.6 

Cockle,    barley    and 

Kornauth    and 

maize  

Arche 





162.7 

T  78 

Rape,    cake,    barley 

Kornauth    and 

.' 

' 

and  maize     .     .     . 

Arche 

— 

— 

167.1 

27.9 

139.2 

Skim  milk  and  flour  l 

Wellmann 

— 

— 

195-9 

60.9 

135.0 

Single  Nutrients 

Starch     

Fingerling  et  al. 

0 

183  o 

Cane  sugar  .... 

Fingerling,  et  al. 

171.3 

5^i 

X  <J£.\J 

166.2 

47.2 

II9.0 

Straw  pulp  .... 

Fingerling,  et  al. 

174.3 

21.7 

152.6 

60.6 

92.O 

Wheat  gluten  .     .     . 

Fingerling,  et  al. 

249.6 

45-6 

204.0 

51.7 

152.3 

Peanut  oil   .     .     .     . 

Fingerling,  et  al. 

4I3-° 

-4.0 

417.0 

30-3 

Palm  oil  

V.  d.  Heide  and 

Klein 

— 

— 

420.6 

105.9 

314.7 

762.  Comparison  of  roughage  and  concentrates.'  —  The  aver- 
age results  recorded  in  the  foregoing  tables  for  the  total  in- 
crease in  metabolism  resulting  from  the  consumption  of  a  unit 
of  dry  matter  —  i.e.,  for  the  so-called  "work  of  digestion" 
in  the  widest  sense  —  are  scarcely  in  accord  with  common  con- 
ceptions. Unconsciously  misled  by  an  unfortunate  termi- 
nology, we  have  been  accustomed  to  think  of  the  more  coarse 

1  Omitting  one  very  restless  animal. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    663 

and  woody  feeding  stuffs,  like  hay,  straw,  stover,  etc.,  as  re- 
quiring a  greater  expenditure  of  energy  in  their  digestion  and 
assimilation  than  the  more  concentrated  and  highly  digestible 
grains,  for  example.  It  may  be  somewhat  surprising,  there- 
fore, to  note  the  relatively  small  differences  in  this  respect  be- 
tween different  classes  of  feeding  stuffs,  as  well  as  the  fact  that, 
in  case  of  cattle,  the  average  is  distinctly  higher  for  the  con- 
centrates than  for  the  roughages,  viz.,  58.75  Therms  per  100 
pounds  dry  matter  as  compared  with  46.54.  While  the  me- 
chanical work  required  for  the  digestion  of  concentrates  is  pre- 
sumably less  than  that  necessary  in  case  of  roughages  on  ac- 
count of  the  greater  expenditure  for  the  mastication  of  the 
latter,  this  difference  appears  to  be  more  than  compensated  for 
by  other  factors,  so  that  on  the  whole  fully  as  great  an  incre- 
ment of  the  heat  production  results  from  the  consumption  of 
the  concentrates.  As  a  class,  concentrates  are  superior  to 
roughage,  not  because  their  consumption  involves  a  less  ex- 
penditure of  energy  but  because  they  contain  more  metaboliz- 
able  energy,  so  that  more  remains  available  for  body  use  after 
the  expenditure  has  been  met. 

763.  Differences  between  feeding  stuffs.  —  But  while  the 
foregoing  results  do  not  show  the  existence  of  the  great  contrast 
between  the  two  chief  classes  of  feeding  stuffs  in  their  effects 
on  the  energy  expenditure  of  the  body  which  seems  at  times  to 
have  been  assumed,  they  nevertheless  reveal  distinct  differences 
even  between  feeding  stuffs  of  the  same  class.  Thus,  among  the 
hays  a  distinct  increase  is  found  from  timothy  hay  with  an 
average  heat  increment  of  35.47  Therms  through  mixed  hay 
and  clover  hay  up  to  alfalfa,  with  an  average  of  53.03  Therms. 
Apparently  the  legumes  cause  a  distinctly  greater  increase  in 
the  metabolism  than  do  the  grasses.  The  chief  difference  be- 
tween the  two  seems  to  lie  either  in  their  effect  upon  the  work 
of  peristalsis  or  in  the  degree  to  which  they  stimulate  the  general 
metabolism.  One  can  hardly  doubt  that  the  latter  is  the 
chief  cause  and  is  naturally  inclined  to  associate  it  with  the 
higher  percentage  of  protein  in  the  legumes.  That  other  causes 
may  also  be  operative,  however,  is  indicated  by  the  result  on 
maize  stover,  which  is  nearly  as  high  as  in  the  case  of  alfalfa 
and  shows  a  similar  distribution  among  the  several  factors. 

Among  the  concentrates  there  may  be  noted  in  particular  the 


664  NUTRITION    OF    FARM    ANIMALS 

marked  effect  of  maize  in  noticeably  increasing  the  metabolism, 
especially  during  standing.  This  result  is  of  interest  in  view 
of  Zuntz  and  Hagemann's  observations  on  the  stimulating 
effect  of  maize  upon  the  metabolism  of  the  horse,  which  were 
also  made  on  the  standing  animal,  although  no  increase  in  the 
minor  muscular  activity  was  reported.  Grain  mixture  No.  i, 
containing  43  per  cent  of  maize  meal,  likewise  showed  a  similar 
effect,  although  with  grain  mixture  No.  2,  containing  60  per 
cent  of  maize,  it  was  much  less  marked,  possibly  on  account 
of  the  lower  content  of  protein  (12.5  as  compared  with  17.5 
per  cent). 

764.  Influence  of  amount  of  feed  consumed.  —  In  the  dis- 
cussions of  the  foregoing  paragraphs  it  has  been  tacitly  as- 
sumed that  both  the  losses  of  chemical  energy  in  the  excreta 
and  the  increment  of  heat  production  consequent  upon  feed 
consumption  are  proportional  to  the  quantity  of  feed  ingested, 
i.e.,  that  the  net  energy  values  per  unit  of  feed  are  substantially 
unaffected  by  the  amount  consumed  or  by  the  plane  of  nu- 
trition of  the  animal. 

This  seems  not  to  accord  with  the  general  belief  that  heavy 
rations  are  relatively  less  effective  than  lighter  ones  and  that 
the  fat  animal  utilizes  its  feed  less  efficiently  than  the  thin 
one.  It  became  clear,  however,  in  the  course  of  the  study,  in 
Part  III,  of  the  feed  requirements  for  various  forms  of  pro- 
duction, that  a  variety  of  factors  are  influential  in  determining 
the  actual  outcome  of  feeding  operations  and  that  diminishing 
returns  from  heavy  or  long  continued  feeding  do  not  neces- 
sarily imply  a  diminishing  efficiency  of  the  feed  as  a  source  of 
body  material  or  energy.  On  the  other  hand,  however,  sur- 
prisingly little  specific  investigation  appears  to  have  been  de- 
voted to  this  fundamental  question. 

Obviously,  differences  in  the  amount  consumed  might  influ- 
ence the  net  energy  value  of  a  feeding  stuff  either  by  affecting 
the  extent  to  which  chemical  energy  is  lost  in  the  excreta  (i.e., 
the  metabolizable  energy)  or  by  affecting  the  magnitude  of  the 
losses  due  to  increased  heat  production. 

Influence  on  metabolizable  energy.  —  That  in  mixed  rations  the 
digestibility  may  suffer  more  or  less  on  heavy  feeding  has  already 
been  shown  in  Chapter  XVI  (722),  notably  in  Eckles'  and  Armsby  and 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    665 

Fries'  experiments  in  which  decreases  of  8  to  10  per  cent  were  observed 
on  rations  varying  in  amount  by  from  42  to  186  per  cent,  although  it 
should  be  noted  that  in  Armsby  and  Fries'  later  experiments  only  sub- 
maintenance  or  moderate  production  rations  were  used. 

On  the  other  hand,  however,  it  was  found  in  the  latter  experiments 
that  the  losses  of  energy  in  the  methane  were  distinctly  greater  on 
the  lighter  rations  so  that  the  differences  in  the  amount  of  feed  con- 
sumed, within  the  limits  of  these  experiments,  failed  to  show  any 
unmistakable  effect  upon  the  quantity  of  energy  actually  liberated 
in  the  body  from  a  unit  weight  of  feed.  Moreover,  it  must  be  borne 
in  mind  that  a  considerable  amount  of  the  additional  energy  secured 
by  the  more  extensive  fermentation  of  the  lighter  ration  is  liberated 
in  the  digestive  tract  as  heat  of  fermentation  and  does  not  enter  into 
the  energy  exchange  of  the  body  tissues,  so  that  the  difference  in  the 
net  nutritive  effect  is  likely  to  be  less  than  that  in  the  metabolizable 
energy  as  ordinarily  denned.  How  far  such  a  compensation  would 
occur  in  more  liberal  feeding  is  difficult  at  present  to  say. 

Influence  on  heat  production.  —  It  is  believed  by  some,  however, 
that,  aside  from  differences  in  digestibility,  etc.,  the  metabolizable 
energy  actually  derived  from  the  feed  is  less  efficiently  utilized  on 
heavy  than  on  light  rations  and  by  fat  than  by  thin  animals,  i.e., 
that  a  unit  of  metabolizable  energy  supplied  yields  less  product. 
This  does  not  appear  exactly  probable,  a  priori.  So  far  as  the  in- 
creased heat  production  is  due  to  mechanical  work  of  digestion,  it 
would  appear  that  it  would  be  substantially  proportional  to  the 
amount  of  dry  matter  consumed,  except  possibly  on  extremely  heavy 
rations.  So  far  as  it  is  due  to  a  stimulation  of  the  body  metabolism 
by  the  digestive  products  resorbed  (367  e)  it  would  appear  more 
likely  that,  in  accordance  with  the  general  laws  of  mass  action,  it 
would  be  a  diminishing  function  of  the  quantity  present.  Certain 
authors,  especially  Grafe  and  Miiller,  have,  it  is  true,  reported  experi- 
ments which  are  claimed  to  demonstrate  a  so-called  "luxus  consump- 
tion" on  heavy  rations  of  carbohydrates,  but  their  results  scarcely 
appear  to  the  writer  entirely  conclusive. 

It  has  already  been  shown  in  Chapter  X  (450)  that  any  heat 
production  arising  from  a  synthesis  of  body  substance,  such  as  that 
of  fat  from  carbohydrates,  for  example,  and  which  might  be  supposed 
to  result  in  a  decreased  efficiency  of  the  feed  energy  on  supermain- 
tenance  as  compared  with  submaintenance  rations,  is  apparently  not 
sufficient  in  amount  as  to  materially  affect  the  net  energy  values  of 
feeding  stuffs.  As  regards  cattle,  the  writer  has  elsewhere  l  discussed 
the  results  of  Kuhn's  and  Kellner's  respiration  experiments  in  their 
bearing  on  this  question,  reaching  the  conclusion  that  their  general 
1  Principles  of  Animal  Nutrition,  pp.  466-471. 


666  NUTRITION    OF    FARM    ANIMALS 

tendency  seems  to  be  in  favor  of  the  hypothesis  that  the  proportion 
of  the  metabolizable  energy  utilized  is  substantially  independent  of 
the  quantity  of  feed,  provided  that  the  changes  in  the  latter  are  not 
so  great  as  to  materially  modify  the  course  of  the  fermentations  in 
the  digestive  tract.  Armsby  and  Fries'  results  on  the  same  species  1 
tend  to  confirm  these  conclusions,  since  they  afforded  no  distinct  evi- 
dence of  an  increase  in  the  heat  production  per  unit  of  feed  as  the 
amount  of  the  latter  was  increased. 

On  the  whole  the  probabilities  seem  to  be  that  the  limit  to 
the  most  efficient  use  of  feed  energy,  in  herbivora  at  least,  is 
set  by  the  capacity  of  the  alimentary  canal  to  digest  and  as- 
similate feed  rather  than  by  the  capacity  of  the  organism  to 
utilize  the  material  transmitted  to  it  by  the  organs  of  resorb- 
tion.  If  this  proves  to  be  the  case,  the  net  energy  values  may  be 
regarded  as  being,  if  not  strictly  constant,  at  least  nearly  so 
over  a  wide  range  of  feeding. 

765.  Influence  of  age,  breed  and  individuality.  —  That  dif- 
ferences due  to  age,  breed  or  "  individuality  "  may  exist  between 
animals  as  regards  the  efficiency  with  which  they  utilize  the 
energy  of  their  feed  and  consequently  as  regards  the  net  energy 
values  of  the  latter  does  not  appear  particularly  probable  a 
priori.     Such  data  on  these  points  as  are  available  have  been 
referred  to  in  Chapters  XI  and  XII,  the  general  conclusion  being 
reached  that  the  evidence  is  insufficient  to  establish  the  existence 
of  any  marked  differences  of  this  sort  except,  perhaps,  in  the 
growth  of  very  young  animals. 

766.  Influence  of  kind  of  production.  —  It  will  not  have  es- 
caped notice  that  the  foregoing  data  regarding  net  energy  values 
relate  entirely  to  the  production  of  body  tissue,  whether  directly 
in  growth  or  fattening  or  indirectly  in  maintenance  or  in  work 
production.     While  it  is  perhaps  unlikely  that  the  values  for 
these  various  purposes  are  stricly  identical,  the  discussions  in 
Chapters  VIII,  X,  XI,  XIV  and  in  the  present  chapter  seem 
to  render  it  probable  that  the  differences  are  not  of  sufficient 
magnitude  to  interfere  seriously  with  the  use  of  these  net  en- 
ergy values  for  the  computation  of  rations  in  practice. 

As  regards  an  important  branch  of  animal  husbandry,  how- 
ever, viz.,  milk  production,  as  was  shown  in  Chapter  XIII, 
scarcely  any  accurate  data  regarding  net  energy  values  are  yet 

1  Jour.  Agr.  Research,  3  (1915),  472-476  and  Fig.  2. 


THE  PRODUCTION  VALUES  OF  FEEDING   STUFFS     667 

available,  although  it  appears  probable  that  they  are  higher 
than  the  corresponding  values  for  tissue  production.  A  tenta- 
tive method  of  utilizing  the  present  net  energy  values  in  com- 
puting the  requirements  of  dairy  cows  was  there  proposed  (605), 
but  definite  experimental  data  are  much  to  be  desired. 

§  3.  THE  COMPUTATION  OF  NET  ENERGY  VALUES 

767.  Importance.  —  It  is  apparent  from  the  foregoing  para- 
graphs that  the  number  of  actual  experimental  determinations 
of  net  energy  values  as  yet  recorded  is  comparatively  small 
and  that  it  can  hardly  be  increased  very  rapidly,  while  it  is 
obviously  impracticable  to  apply  the  laborious  method  of  res- 
piration and  calorimeter  experiments  to  all  the  great  number 
of  feeding  stuffs  now  in  use.     Determinations  of  the  metabo- 
lizable  energy,  in  which  at  least  the  energy  of  the  feeding  stuffs 
and  of  the  visible  excreta  has  been  determined,  are  rather  more 
numerous,  while  there  are  on  record  the  results  of  a  great  num- 
ber of  digestion  experiments  in  which  no  determinations  of 
energy  were  made.     It  is  highly  important  that  the  mass  of 
statistical  data  thus  accumulated,  and  summarized  in  tables  of 
the  composition  and  digestibility  of  feeding  stuffs,  should  not 
be  incontinently  thrown  overboard  simply  because  a  newer 
point  of  view  has  revealed  more  clearly  its  deficiencies.     On  the 
contrary,  it  should  be  utilized  to  the  fullest  extent  possible,  in 
connection  with  the  as  yet  rather  meager  results  of  the  more 
recent   experimental  methods,  for  computing   the  net  energy 
values  of  such  feeding  stuffs  as  have  not  yet  been  subjected 
to  direct  investigation. 

Computation  from  digestible  nutrients 

768.  Kellner's  investigations.  —  To  Kellner  is  due  the  first 
attempt  to  make  practical  application  of  the  conception  of  the 
feed  as  the  source  of  energy  to  the  body.     In  1880,  in  his  in- 
vestigations upon  the  relations  between  muscular  activity  and 
metabolism  in  the  horse  (637)  he  determined  the   additional 
amount  of  work  which  the  animal  was  able  to  perform  as  a 
result  of  the  addition  to  his  rations  of  starch  and  of  fat.     He 
expressed  his  results  in  terms  of  the  percentage  of  the  energy 


668 


NUTRITION  OF  FARM  ANIMALS 


of  the  starch  or  fat  which  was  recovered  as  useful  work  and 
called  attention  to  the  desirability  of  determinations  of  the 
heats  of  combustion  of  nutrients  and  feeding  stuffs.  Sixteen 
years  later,  after  Rubner  had  published  his  fundamental  work 
on  the  replacement  values  of  nutrients,  and  Zuntz  and  his  as- 
sociates (385,  651-656)  had  begun  their  investigations  upon  the 
metabolism  of  the  horse  from  the  standpoint  of  energy,  Kellner 
was  able  to  return  to  the  subject  and  undertake  the  extensive 
investigations  with  cattle  frequently  cited  on  previous  pages. 

769.  Energy  values  of  digestible  nutrients.  —  Taking  as  his 
point  of  departure  the  digestible  nutrients  of  feeding  stuffs, 
Kellner  sought  first  to  determine  the  net  energy  values  of  the 
digestible  protein,  carbohydrates  and  fats  for  cattle  by  adding 
these  substances  in  as  pure  form  as  possible  to  a  basal  ration  in 
the  manner  already  described  (449).  The  results  with  cattle 
obtained  in  this  way  on  starch,  straw  pulp,  sugar,  wheat  gluten 
and  oil  are  included  in  Table  202  (760) .  In  that  table,  however, 
these  materials  are  regarded  in  the  light  of  feeding  stuffs  and 
the  energy  losses  and  net  energy  values  relate  to  the  substance 
as  a  whole  and  include  all  its  effects.  For  his  purpose,  how- 
ever, Kellner  computed  the  net  energy  values,  not  of  these  sub- 
stances as  a  whole  but  of  the  protein,  carbohydrates  and  fat 
which  determinations  of  digestibility  showed  to  have  been 
resorbed  from  them,  with  the  following  results.1 

TABLE   205.  —  NET   ENERGY  VALUES   OF   DIGESTIBLE   NUTRIENTS   FOR 

CATTLE 


PER  100  POUNDS 
OF  DRY  MATTER 

PER  CENT 
OF  METAB- 
OLIZABLE 
ENERGY 

Protein      

Therms 
IOI.6 

AC    g 

Starch  and  crude  fiber 

IO7  I 

64    I 

Cane  sugar     

8l  2 

<a  6 

Ether  extract 
of  roughage 

2O4  I 

CA    i 

of  grains  and  their  by-products       .... 
of  feeding  stuffs  containing  over  5  per  cent 
fat      

227.3 

2<8  6 

56.8 

64  6 

.  Vers.  Stat.,  63  (1900),  1-474;   Ernahrung  landw.  Nutztiere,  6th  Ed. 


95-159- 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    669 


Obviously  the  percentages  in  the  last  column  are  analogous 
to  those  obtained  by  Rubner  and  by  Lusk  (759)  in  experi- 
ments on  dogs,  and  the  differences  between  the  two  sets  em- 
phasize the  differences  in  the  nutritive  processes  of  the  two 
species. 

770.  Correction  for  crude  fiber.  —  Kellner  then  proceeded  to 
test  the  applicability  of  these  factors  to  the  ordinary  feeding 
stuffs  of  cattle.  With  a  certain  number,  notably  the  oil  meals, x 
the  net  energy  values  as  computed  by  the  use  of  his  factors 
from  the  amounts  of  protein,  carbohydrates  and  fat  actually 
digested  showed  a  close  agreement  with  those  found  in  direct 
experiments  with  the  respiration  apparatus.  The  digestible 
nutrients  of  these  materials  were  of  full  value  as  compared  with 
pure  starch,  gluten  or  oil. 

TABLE  206.  —  NET  ENERGY  VALUES  or  OIL  MEALS  FOR  CATTLE 
Per  100  Pounds  Dry  Matter 


COMPUTED 

OBSERVED 

DIFFERENCE 

Cottonseed  meal 

Therms 
86  4 

Therms 
84  8 

% 
i  8 

Peanut  meal 

81  4 

81  6 

-4-  O  2 

Palmnut  meal  

77  3 

78  Q 

+  20 

Linseed  meal 

SA  7 

82  o 

On  the  other  hand,  a  striking  contrast  with  the  oil  meals  is 
afforded  by  the  roughages,  whose  net  energy  values  as  directly 
determined  were  much  lower  than  those  computed,  the  deficit 
ranging  from  30  per  cent  to  80  per  cent  and  being  greatest 
with  the  coarsest  and  least  digestible  materials.2  Kellner  found 
this  deficit  to  be  more  nearly ,  proportional  to  the  crude  fiber 
than  to  any  other  ingredient  of  the  feeding  stuffs,  ranging 
from  46.3  Therms  to  76.7  Therms  per  100  pounds  of  total  fiber. 
By  subtracting  the  average  of  61.7  Therms  from  the  computed 
net  energy  values,  results  were  obtained  which  agreed  well 
with  those  secured  in  direct  experiments  in  the  case  of  the 
hays  but  still  showed  considerable  discrepancies  for  the  straws, 
as  follows :  — 


1  Loc.  cit.,  p.  1 60. 


2  Ibid.,  p.  162. 


6yo 


NUTRITION  OF  FARM  ANIMALS 


TABLE  207.  —  NET  ENERGY  VALUES  or  ROUGHAGES  FOR  CATTLE 
Per  100  Pounds  Dry  Matter 


COMPUTED 
WITH  COR- 
RECTION 
FOR  CRUDE 
FIBER 

OBSERVED 

DIFFER- 
ENCE 

Wheat  straw 
Sample  & 

Therms 
16  I 

Therms 
91 

Per  Cent 
—  A1.  A. 

Sample  b  

7  ^ 

10  4. 

+  ^8  O 

Oat  straw 

23  O 

28  t; 

1     2A  I 

Barley  straw 

28A 

•7-7     Q 

+   IQ  ^ 

Meadow  hay 
Sample  a  
Sample  b                 ... 

35-4 

4.8  3 

35-o 

A  7  I 

-    i-3 

—      2  ^ 

Clover  hay   

"Grass  hay" 

35-3 

•2Q     A 

36.8 

*6  7 

+    4-1 

—      7  O 

Rowen 

^6    I 

•2-2    Q 

—    6  o 

For  finer  materials  like  chaff,  presumably  requiring  a  less 
expenditure  for  mastication,  3 1.8  Therms  per  100  pounds  of  total 
crude  fiber  was  deducted.  For  green  forage  containing  16  per 
cent  or  more  of  crude  fiber  the  same  deduction  was  made  as  for 
dry  forage  and  for  that  containing  4  per  cent  or  less  of  crude 
fiber,  the  same  as  for  chaff,  while  between  these  limits  a  sliding 
scale  was  used.  This  correction  for  crude  fiber  was  applied 
only  to  roughage. 

Kellner  ascribed  this  apparent  effect  of  crude  fiber  largely 
to  the  mechanical  work  required  for  its  mastication  and  trans- 
portation through  the  alimentary  canal,  but  in  part  also  to  the 
fermentations  to  which  it  is  subject ;  in  other  words,  he  ascribed 
it  to  the  so-called  "  work  of  digestion."  In  reality,  however, 
the  crude  fiber  can  be  regarded  only  as  a  convenient  empirical 
measure  of  the  differences  between  concentrates  such  as  the 
oil  meals  and  roughage.  It  has  already  been  shown  from  Kell- 
ner's  own  experiments  and  from  others  (762)  that  the  loss  of 
energy  in  this  way,  far  from  being  greater,  is  on  the  whole  rather 
less  with  roughages  than  with  concentrates  and  that  the  me- 
chanical work  of  the  digestive  organs  is  probably  a  rather  small 
factor  in  it.  Roughages  have  relatively  less  net  energy  value,  not 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    671 

because  they  contain  much  crude  fiber  which  causes  much  me- 
chanical work  but  because  the  feeding  stuff  as  a  whole  stimulates 
the  metabolism  and  causes  a  loss  of  energy  which,  though  not 
greater,  or,  it  may  be,  even  less,  than  in  the  case  of  concentrates, 
is  deducted  from  a  much  smaller  amount  of  metabolizable  energy 
supplied  by  the  less  amount  of  substances  digested. 

771.  Relative  values  for  concentrates.  —  That  the  crude  fiber 
is  far  from  being  the  only  determining  factor  of  the  amount  of 
energy  expended  in  consequence  of  feed  consumption  is  clearly 
shown  by  the  majority  of  Kellner's  experiments  on  concentrates 
and  roots.  Although  with  the  oil  meals  a  close  agreement  of 
the  observed  and  computed  results  was  obtained,  in  most  in- 
stances the  observed  net  energy  value  fell  considerably  short  of 
that  computed  by  the  use  of  the  factors  of  Table  205.  The  fol- 
lowing table  contains  the  results  of  the  comparisons  thus  far 
reported.1  They  show  clearly  that  the  digestible  organic 
matter  has  a  very  unequal  value  in  different  classes  of  feeding 
stuffs,  but  a  comparison  with  the  percentages  of  crude  or  of 
digestible  nutrients  also  shows  that  the  crude  fiber  fails  in 
these  cases  as  a  measure  of  the  differences. 

TABLE  208.  —  OBSERVED  NET  ENERGY  VALUES  FOR  CATTLE  AS  PER  CENT 
OF  COMPUTED 

Rye  meal 93.5  per  cent 

Bean  meal 94.4  per  cent 

Rye  bran 79.0  per  cent 

Wheat  bran 77.3  per  cent 

Dried  brewers'  grains 84.3  per  cent 

Dried  distillers'  grains 88.2  per  cent 

Rice  meal 108.4  per  cent 

Malt  sprouts 85.8  per  cent 

Potatoes 98.0  per  cent 

Mangolds 86.9  per  cent 

Fresh  beet  pulp 94.1  per  cent 

Dried  beet  pulp 78.4  per  cent 

In  computing  the  net  energy  values  of  concentrates,  there- 
fore, Kellner  made  no  correction  for  the  crude  fiber,  but  instead 
corrected  in  each  case  the  value  computed  from  the  digestible 
nutrients  by  multiplying  it  by  a  percentage  (Wertigkeit)  taken 
directly  from  the  foregoing  table  when  possible  or  estimated 

1  Ernahrung  landw.  Nutztiere,  pp.  165-167. 


672  NUTRITION  OF  FARM  ANIMALS 

from  it.  For  example,  the  net  energy  values  of  alfalfa  hay  and 
of  wheat  bran  having  the  composition  and  digestibility  given 
by  Allen  1  would  be  computed  as  follows :  — 

TABLE  209.  —  COMPUTATION  OF  NET  ENERGY  VALUES  PER  100  POUNDS 
ACCORDING  TO  KELLNER 

Alfalfa  Hay 

Digestible  protein 10.58  X  1.016  =  10.75  Therms 

Digestible  carbohydrates 37-33  X  1.071  =  39.98  Therms 

Digestible  ether  extract 1.38  X  2.041  =    2.82  Therms 

53.55  Therms 

Total  crude  fiber 25.00  X  0.617  =  15.43  Therms 

Net  energy  value 38.12  Therms 

Wheat  Bran  (Relative  Value  77  %) 

Digestible  protein 12.01  X  1.016  =12. 20  Therms 

Digestible  carbohydrates 41.23  X  1.071  =  44.16  Therms 

Digestible  ether  extract 2.87  X  2.273  =    6.52  Therms 

62.88  Therms 
Net  energy  value 62.88  X  0.77     =  48.42  Therms 

772.  Starch  values.  —  Kellner's  results  were  in  reality  net 
energy  values,  as  is  evident  from  the  method  by  which  they 
were  obtained.  In  order,  however,  to  avoid  the  use  of  the 
large  numbers  required  to  express  the  net  energy  values  of 
rations  in  Calories,  and  also  to  avoid  the  introduction  of  un- 
familiar terms,  he  converted  them  for  practical  use  into  what  he 
called  "  starch  values."  The  starch  value  of  a  feeding  stuff 
may  be  briefly  defined  as  the  amount  of  pure  starch  (assumed  to 
be  perfectly  digested)  which  has  the  same  net  energy  value. 
Thus,  Kellner's  table  gives  the  starch  value  of  maize  meal  as 
£1.5  kilograms  per  100  kilograms,  or  81.5  pounds  per  100  pounds. 
One  pound  of  starch,  according  to  Kellner's  results  (769),  has  a 
net  energy  value  of  1071  Cals.  The  starch  value  of  81.5  given 
for  maize  meal,  therefore,  is  equivalent  to  a  net  energy  value 
of  1071  X  81.5  =  87,286  Cals.,  or  87.29  Therms,  per  100  pounds 
and  conversely  the  starch  values  of  the  alfalfa  hay  and  wheat 
bran  of  the  previous  paragraph  would  be  35.59  and  45.21,  re- 
spectively.2 

1  U.  S.  Dept.  Agr.,  Farmers'  Bulletin  22  (Rev.),  1901,  pp.  &-g. 

2  In   other  words,  Kellner's   starch  values  multiplied   by  1.071  =  net  energy 
values  per  100  Ib. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    673 

Kellner's  starch  values  yield  numbers  of  the  same  order  of 
magnitude  as  those  already  familiar  in  tables  of  digestible  nu- 
trients and  avoid  unfamiliar  units.  They  accomplish  these 
ends,  however,  by  ignoring  the  whole  conception  on  which  the 
system  is  built  up,  while  some  striking  instances  in  recent  lit- 
erature have  shown  that  it  is  not  always  easy,  even  for  ex- 
perts, to  avoid  confusion  of  thought  in  connection  with  their 
use.  It  appears  to  the  writer  to  have  been  an  unfortunate  con- 
cession to  attempt  to  express  quantities  of  energy  in  terms  of 
matter.  He  believes  the  intelligent  feeder  can  readily  learn 
to  use  units  of  energy  in  his  computation  of  rations,  as  not  a 
few  have  already  done,  and  that  there  are  manifest  advantages 
in  going  over  frankly  and  boldly  to  a  system  based  on  energy, 
while  the  objection  to  the  use  of  large  numbers  is  readily  avoided 
by  the  employment  of  a  larger  unit  of  energy,  the  Therm  (308). 
Net  energy  values  expressed  in  Therms  per  100  pounds  are  of 
the  same  order  of  magnitude  as  the  familiar  figures  for  di- 
gestible nutrients,  and  even  if  100  kilograms  be  made  the 
basis  of  calculation  they  are  not  inconveniently  large.  For 
these  reasons,  energy  values  of  feeding  stuffs  in  the  present 
volume  are  expressed  in  Therms  per  100  pounds. 


Computation  from  digestible  organic  matter 

773.  Independent  of  chemical  composition.  —  It  is  apparent 
from  the  foregoing  description  of  Kellner's  somewhat  compli- 
cated method  that  it  is  essentially  based  on  the  digestible 
protein,  carbohydrates  and  fats  of  the  older  relative  values 
(705-710),  while  it  involves  in  its  execution  certain  more  or 
less  empirical  corrections  which  are  at  bottom  simply  methods 
of  applying  the  average  net  results  on  typical  feeding  stuffs 
to  other  materials.  Armsby  and  Fries x  have  proposed  a 
method  which  seeks  to  attain  the  same  end  more  directly  and 
simply,  relating  the  energy  content  and  the  necessary  deduc- 
tions to  the  total  dry  matter  or  total  digestible  matter  of  the 
feeding  stuff  independently  of  its  chemical  composition. 

The  energy  content  of  a  feeding  stuff  is  just  as  definite  a 
quantity  as  its  content  of  protein,  carbohydrates,  or  fats,  and 

1  Jour.  Agr.  Research,  3  (1915),  486. 
2  X 


674  NUTRITION  OF  FARM  ANIMALS 

it  is  entirely  possible  to  trace  the  distribution  of  that  energy 
in  the  body  quite  independently  of  any  knowledge  of  the  chemical 
composition  of  the  material.  Not  only  so,  ^  but  it  is  believed 
that  in  discussing  energy  values  there  are  distinct  advantages 
as  regards  simplicity,  and  perhaps  also  as  regards  accuracy,  in 
cutting  loose  as  far  as  possible  from  the  conventional  data  re- 
garding chemical  composition  and  digestion  coefficients  and  in 
dealing  directly  with  quantities  of  energy. 

This  statement  is  by  no  means  to  be  understood  to  stigmatize 
comparisons  based  on  chemical  methods  as  either  valueless  or  super- 
fluous. The  problems  of  nutrition  are  too  complex  and  too  difficult 
for  us  to  refuse  any  light  that  can  be  thrown  on  them  by  any  method, 
and  the  energy  relations  touch  only  one  phase  of  them.  The  point 
is  that  in  whatever  degree  their  energetic  aspects  can  be  separated 
from  their  chemical  aspects,  to  that  extent  we  possess  two  inde- 
pendent methods  of  approach  to  them. 

774.  Method  of  computation.  —  As  already  pointed  out, 
the  net  energy  value  of  a  feeding  stuff  is  equal  to  its  me- 
tabolizable  energy  minus  the  heat  production  caused  by  its 
consumption.  It  has  been  shown  (753)  that  the  metabolizable 
energy  of  a  feeding  stuff,  when  not  determined  directly,  may 
be  computed  approximately  from  the  total  digestible  organic 
matter  by  multiplying  by  a  proper  factor.  If  from  this 
result  there  be  subtracted  the  energy  expenditure  due  to 
feed  consumption,  either  as  directly  determined  or  as  esti- 
mated from  that  of  similar  feeds,  the  remainder  is  approx- 
imately the  net  energy  value.  Thus  in  the  same  two  feeding 
stuffs  just  used  to  illustrate  Kellner's  method  each  pound  of  di- 
gestible organic  matter,  according  to  the  averages  on  previous 
pages  (753-755),  would  contain  1.60  Therms  of  metabolizable 
energy  in  the  hay  and  1.77  Therms  in  the  bran;  the  average 
losses  of  energy  in  heat  production  per  pound  of  dry  matter 
would  be  for  the  hay  0.5303  Therm  and  for  the  bran  0.5339 
Therm,  and  the  computation  of  the  net  energy  values  would  be 
as  follows : l  - 

1  The  digestible  protein,  carbohydrates  and  fats  enter  into  the  calculation  simply 
as  a  means  of  obtaining  the  total  digestible  organic  matter  when,  as  is  usually  the 
case,  this  is  not  reported  separately.  If  the  latter  is  the  case,  then  the  computa- 
tion is,  as  stated  above,  independent  of  the  chemical  composition. 


THE  PRODUCTION  VALUES  OF  FEEDING   STUFFS     675 


TABLE  210.  —  COMPUTATION  OF  NET  ENERGY  VALUES  PER  100  POUNDS 
ACCORDING  TO  ARMSBY  AND  FRIES 


ALFALFA  HAY 

WHEAT  BRAN" 

Total  dry  matter      .     . 
Digestible 
Protein 

91.6    Ib. 
10  58  Ib 

,      88.5    Ib. 

Carbohydrates      .     . 
Fats  
Total  digestible  organic 
matter   .... 

Metabolizable  energy   . 
Loss  in  heat  production 
Net  energy  value     .     . 

37-33  Ib. 
1.38  Ib. 

49.29  Ib. 

49.49  X  i.  60      =  78.86  Therms 
91.60  X  0.5303  =  48.58  Therms 
30.28  Therms 

41.23  Ib. 
2.87  Ib. 

56.11  Ib. 

56.11  X  1.77      =  99.31  Therms 
88.50  X  0.5339  =  47.25  Therms 
52.06  Therms 

The  same  method  of  computation  is  of  course  applicable  to 
other  species  than  cattle,  so  far  as  the  meager  data  at  hand 
permit.  The  results  of  such  computations,  based  upon  the 
average  composition  and  digestibility  of  American  feeding 
stuffs,  are  contained  in  the  tables  of  the  Appendix. 

Computation  of  net  energy  values  for  the  horse 

775.  Zuntz  and  Hagemann's  method.  —  The  method  em- 
ployed by  Zuntz  and  Hagemann  1  for  computing  net  energy 
values  for  the  horse  (758)  is  substantially  similar  to  that  just 
illustrated  for  cattle.     The  metabolizable  energy  is  estimated 
from  the  digestible  nutrients  and  from  it  is  subtracted  the  com- 
puted energy  expenditure  due  to  the  consumption  of  the  feed. 

776.  Metabolizable  energy.  —  From  the  results  of  five  digestion 
and  metabolism  experiments  on  rations  of  oats,  hay  and  straw  in 
different  proportions  made  at  intervals  between  1888  and  1891,  they 
compute  the  metabolizable  energy  of  the  total  digestible  nutrients 
(including  the  digested  fat  multiplied  by  2.4)  to  avenge  3.96  Cals. 
per  gram,  corresponding  to  3.99  Cals.  per  gram  digestible  organic 
matter  as  computed  by  the  writer  in  Table    188    (749).    In    the 
respiration  experiments,  the  digestible  nutrients  were  not  determined 
directly  but  were  estimated  by  combining  the  results  of  the  same 
five  digestion  and  metabolism  experiments  in  various  ratios  according 
to  the  proportion  of  oats,  hay  and  straw  consumed. 

777.  Increment  of  heat   production:  —  Experiments    upon   man, 
made  by  Magnus-Levy  in  Zuntz's  laboratory,  had  previously  shown 

1  Landw.  Jahrb.,  27  (1898);  Ergzbd.  Ill,  211-236,  276-279,  418. 


676  NUTRITION  OF  FARM  ANIMALS 

that  food  consumption  increased  the  total  metabolism  by  about  g  per 
cent  of  the  metabolizable  energy  of  the  food  eaten.  Zuntz  and  Hage- 
mann  assume  that  this  result  is  applicable  to  the  digestible  nutrients 
of  the  feed  of  the  horse. 

In  addition,  it  was  found  that  hay  produced  a  much  more  marked 
effect  than  did  grain  in  augmenting  the  heat  production  of  the  horse 
as  estimated  from  the  respiratory  exchange,  which  was  determined 
by  means  of  the  Zuntz  apparatus  in  short  periods  at  various  intervals 
after  the  consumption  of  more  or  less  diverse  rations,  a  small  correc- 
tion being  added  for  cutaneous  and  intestinal  respiration.  This  dif- 
ference is  ascribed  to  the  crude  fiber  of  the  hay  and  its  amount  is 
computed  to  be  2.086  Cals.  per  gram.  The  energy  expended  in  the 
mastication  of  the  feed  is  likewise  related  to  its  crude  fiber  content, 
being  estimated  at  0.565  Cals.  per  gram.  The  total  heat  increment 
per  gram  of  crude  fiber,  therefore,  is  estimated  at  2.65  Cals.  per  gram. 

778.  Computation  of  net  energy  value.  —  In  brief,  Zuntz 
and  Hagemann  compute  the  heat  production  due  to  the  con- 
sumption of  feed  by  the  horse  to  be  equal  to  9  per  cent  of 
the  metabolizable  energy,  estimated  at  the  rate  of  3.96  Cals. 
per  gram  of  digestible  nutrients,  plus  2.65  Cals.  for  each  gram 
of  total  crude  fiber  present,  and  by  subtraction  of  these  amounts 
from  the  metabolizable  energy  obtain  the  net  energy  value. 

The  method  of  computation  may  be  conveniently  illustrated 
from  the  data  given  by  Langworthy  1  for  timothy  hay.  Zuntz 
and  Hagemann 's  factors,  recalculated  per  100  pounds  for 
convenience,  become  for  metabolizable  energy  1.796  Therms 
and  for  crude  fiber  1.202  Therms.  On  this  basis  the  calculation 
of  the  heat  production  due  to  the  hay  would  be  as  follows :  — 

TABLE  211.  —  COMPUTATION  OF  NET  ENERGY  VALUE  PER  100  POUNDS 
FOR  THE  HORSE 

Digestible  nutrients 

Protein      .........  1.25  Ib. 

Crude  fiber 12.39  Ib. 

Nitrogen -free  extract 21.29  Ib.  .tUTTi;?   ' 

Fat  (1.18  X  2.4) 2.83  Ib. 

37-72  Ib. 
Total  crude  fiber 29.00  Ib. 

Metabolizable  energy 1.796  Therms  X  37-72  =  67.75  Therms 

Increase  of  metabolism 

9  per  cent  of  metabolizable  energy  67.75  Therms  X  0.09  =  6.10  Therms 
Additional  for  crude  fiber  .  .  .  1.202  Therms  X  29.00  =  34.86  Therms 
Total 40.96  Therms 

Net  energy  value 26.79  Therms 

1  U.  S.  Dept.  Agr.,  Office  of  Expt.  Stas.,  Bui-  125,  p.  14. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    677 

As  is  evident  from  the  methods  by  which  the  factors  were 
reached,  this  method  of  calculation  is  not  strictly  exact,  but  the 
authors  believe  it  to  be  a  sufficiently  close  approximation  on 
which  to  base  computations  of  rations  in  practice. 

Zuntz  and  Hagemann's  method  of  computation  has  been  the  subject 
of  considerable  criticism,  the  two  principal  points  being,  first  their 
estimate,  based  upon  the  results  of  experiments  on  man,  of  9  per  cent 
for  the  effect  of  the  digestible  nutrients,  and  second,  and  more  es- 
pecially, the  assumption  that  the  metabolism  for  24  hours  may  be  com- 
puted from  the  results  of  comparatively  short  respiration  experiments. 
Qualitatively,  Zuntz  and  Hagemann  have  clearly  demonstrated 
the  very  considerable  increase  of  energy  metabolism  in  the  horse 
during  the  digestion  of  his  feed,  as  well  as  the  fact  that  this  increase 
is  relatively  greater  with  roughage  than  with  grain,  and  they  were 
the  first  to  point  out  that  this  effect  must  be  taken  into  account  in 
estimating  the  values  of  feeding  stuffs.  There  may  be  a  difference 
of  opinion  as  to  the  quantitative  accuracy  of  their  figures  and  cer- 
tainly investigations  by  more  direct  methods,  involving  fewer  assump- 
tions and  complex  calculations,  are  greatly  to  be  desired,  but  until 
such  results  are  obtained,  we  may  continue  to  use  provisionally  those 
reached  in  the  manner  just  described. 

i  779.  Wolff's  method  of  computation.  —  His  extensive  investiga- 
tions upon  the  working  horse  made  at  Hohenheim  in  1877  to  1894 
and  antedating  the  investigations  thus  far  mentioned,  led  Wolff  to 
a  still  simpler  approximate  method  of  estimating  the  relative  net 
energy  values  of  feeds  for  the  horse. 

It  was  shown,  on  the  average  of  a  considerable  number  of  compari- 
sons, that  the  digestible  nutrients  from  roughage  were  less  efficient 
both  for  work  production  and  for  maintenance  than  were  those  derived 
from  grain.  Wolff  found,  however,  that  if  the  digestible  crude  fiber 
were  omitted  from  the  comparisons,  the  ratio  between  the  fiber-free 
nutrients  and  the  work  performed  was  comparatively  uniform  and 
also  that  this  assumption  yielded  uniform  results  for  the  amount  of 
fiber-free  nutrients  necessary  for  maintenance.  He  therefore  con- 
cluded that,  the  crude  fiber  in  the  rations  of  the  horse  was  apparently 
valueless  and  that  the  remaining  digestible  nutrients  might  be  re- 
garded as  of  equal  value  whether  derived  from  grain  or  from  roughage. 
Expressed  in  the  light  of  our  present  conceptions,  this  is  practically 
equivalent  to  saying  that  the  net  energy  value  is  proportional  to  the 
amount  of  fiber-free  nutrients. 

Wolff  is  careful  to  say  that  the  digestible  crude  fiber  is  apparently 
valueless,  and  virtually  regards  the  amount  of  crude  fiber  as  furnish- 
ing a  convenient  empirical  measure  of  the  difference  in  the  value  of 


678  NUTRITION  OF  FARM   ANIMALS 

the  digestible  nutrients  of  roughage  as  compared  with  those  of  grain. 
That  such  is  the  case  is  doubtless  explained  in  part  by  the  rather 
limited  variety  of  feeding  stuffs  employed  in  the  experiments.  The 
roughage  was  meadow  hay  with,  in  some  cases,  a  small  addition  of 
straw,  while  the  grain  was  usually  oats,  partially  replaced  in  some 
instances  by  other  feeds.  Whether  the  same  relation  between  fiber- 
free  nutrients  and  work  done  would  hold  in  widely  different  rations 
is  not  apparent. 

Wolff's  results  are  relative  only.  They  do  not  show  the  actual 
amount  of  net  energy  in  the  rations  but  only  that  it  was  proportional 
to  the  fiber-free  nutrients.  The  energy  content  of  the  latter  would 
differ  considerably  from  the  net  energy  as  computed  by  Zuntz  and 
Hagemann's  method,  first  because  it  does  not  include  the  deduction 
of  9  per  cent  of  the  metabolizable  energy,  and  second,  because  it 
assumes  a  uniform  value  of  zero  for  crude  fiber,  while  Zuntz  and  Hage- 
mann's method  gives  the  crude  fiber  a  negative  value  if  it  has  a  di- 
gestibility of  less  than  55  per  cent.  Values  computed  according 
to  Wolff's  method  from  the  fiber-free  nutrients  would  therefore  con- 
siderably exceed  Zuntz  and  Hagemann's  figures. 


§  4.  PRODUCTION  VALUES  AS  REGARDS  PROTEIN 

Relative  values  of  proteins 

780.  Differences  in  proteins.  —  As  appears  from  the  discus- 
sions of  the  preceding  section,  the  production  values  of  feeding 
stuffs  as  regards  energy  may  already  be  formulated  with  some  de- 
gree of  accuracy,  although  further  investigation  is  much  needed. 

Concerning  the  production  values  as  regards  protein,  the 
situation  is  far  less  satisfactory.  For  years  the  protein  of 
feeding  stuffs  has  been  treated  as  if  it  were  a  single  chemical 
substance ;  i.e.,  the  different  proteins  known  to  exist  in  feeding 
stuffs  have  been  assumed  to  have  substantially  equal  nutritive 
values.  The  more  recent  investigations  into  the  chemistry 
and  physiology  of  the  proteins,  however,  have  resulted  in  an 
entire  change  in  the  point  of  view.  As  has  been  fully  shown 
in  previous  chapters  (340,  398,  465,  552),  it  is  the  constituent 
amino  acids  into  which  the  proteins  are  split  in  digestion  which 
are  the  materials  out  of  which  body  protein  is  constructed,  and 
the  processes  of  maintenance,  growth  or  milk  production  re- 
quire for  their  support,  not  proteins  as  such,  but  certain 
amounts  and  proportions  of  such  of  the  amino  acids  as  cannot 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    679 

be  synthesized  in  the  body.  In  place  of  a  single  requirement  for 
protein,  it  would  appear  that  there  must  be  substituted  a  num- 
ber of  separate  amino  acid  requirements,  a  deficiency  as  regards 
any  one  of  which  may  constitute  a  limiting  factor. 

781.  Incomplete  and  unbalanced    proteins.  —  As   appeared 
in  Chapter  I  (50)  certain  vegetable  proteins  may  be  classed 
as  incomplete  proteins  in  the  sense  that   they  lack   entirely 
one  or  more  of  the  amino  acids  characteristic  of  proteins  in 
general.     The  classic   example    of   an    incomplete   protein    is 
gelatin,  which  lacks  ty rosin  and    tryptophan  and  which  has 
long  been  known  to  be  incapable  by  itself  of  maintaining  the 
stock  of  body  protein  in  an  animal.     A  similar  case  among  the 
vegetable  proteins  which  has  been  much  discussed  is  the  zein 
of  maize,  which  yields  neither  lysin,  glycin  nor  tryptophan  on 
hydrolysis  and  which  is  incapable  of  supporting  either  main- 
tenance (399)  or  growth  (465).     Still  another  instance  is  afforded 
by  the  gliadin  of  wheat  (465),  which  lacks  lysin  and  which, 
while  adequate  for  maintenance,  is  unable  to  support  growth. 
Furthermore,  the  proteins  of  the  cereal  grains  in  general,  while 
not  incomplete  in  the  sense  of  absolutely  lacking  certain  amino 
acids,  may,  from  the  standpoint  of  animal  nutrition,  be  called 
unbalanced  in  that,  as  compared  with  the  body  proteins,  they 
are  relatively  rich  in  glutamic  acid  and  therefore  correspondingly 
deficient   in   other   constitutents,   including   those   ingredients 
which,  like  lysin  in  particular,  appear  to  be  essential  to  growth. 
It  appears  evident  that  in  the  conversion  of  a  unit  weight  of 
such  a  protein  into  body  protein,  a  considerable  portion  of  the 
amino  acid  present  in  excess  must  undergo  deaminization  (233) 
and  be  substantially  a  waste  product  so  far  as  the  protein  re- 
quirement of  the  body  is  concerned,  although  it  may  of  course 
serve  as  a  source  of   energy.     Quantitative  results  as   to  the 
maximum  percentage  utilization  of  individual  proteins,  how- 
ever, are  not  yet  available. 

782.  Application  of  results.  —  But  while  the  general  validity  of 
the  newer  point  of  view  seems  well  established,  it  does  not  appear 
possible  as  yet  to  utilize  it  in  establishing  net  protein  values  for 
feeding  stuffs  comparable  to  the  net  energy  values  discussed  in 
§  2  of  this  chapter.     For  this  there  are  three  principal  reasons. 

First,  sufficient  knowledge  of  the  proteins  of  feeding  stuffs 
is  lacking.     Although  the  constituents  of  a  considerable  number 


680  NUTRITION  OF  FARM  ANIMALS 

of  vegetable  proteins  derived  from  seeds  is  known,  those  con- 
tained in  roughages  and  in  roots  have  not  yet  been  investigated, 
although  a  beginning  has  been  made  1  in  determining  the  pro- 
portions of  the  different  groups  of  amino  acids  which  are  yielded 
by  the  total  nitrogenous  matter  (crude  protein)  of  various  feed- 
ing stuffs. 

Second,  as  has  appeared  in  previous  chapters,  such  informa- 
tion as  is  available  respecting  the  protein  requirements  of  farm 
animals  has  been  derived  from  experiments  in  which  only  the 
total  protein  supplied  was  considered  without  reference  to  its 
kind.  Practically  no  knowledge  is  available  as  to  the  amino  acid 
requirements  of  the  various  farm,  animals  for  different  purposes. 

Third,  even  were  the  production  values  of  the  various  single 
proteins  known,  it  would  not  be  possible  to  estimate  from  them 
the  production  values  of  the  mixed  proteins  of  feeding  stuffs, 
since  a  deficiency  in  one  protein  might  be  compensated  by  a 
surplus  in  another  and  the  mixture  show  a  much  higher  pro- 
duction value  than  either  of  its  ingredients  separately.  Thus, 
as  already  noted,  the  value  of  wheat  gliadin,  which  lacks  lysin, 
is  practically  zero  for  growth,  while  as  part  of  a  mixture  with 
other  proteins  supplying  lysin  it  may  have  a  high  value,  the 
replacement  of  25  per  cent  of  it  by  lactalbumin,  for  example, 
rendering  the  mixture  fully  adequate  to  support  normal  growth. 
Each  particular  mixture  of  proteins  would  have  its  own  pro- 
duction value,  which  might  differ  widely  from  the  mean  of  the 
values  for  the  individual  constituents. 

The  qualitative  differences  in  proteins  are  doubtless  of  much 
significance,  and  the  researches  in  progress  can  hardly  fail 
ultimately  to  lead  to  a  more  rational  method  of  valuation  than 
that  now  in  use,  but  as  yet  they  do  not  afford  an  adequate 
basis  for  expressing  the  values  of  feeding  stuffs  in  general  as 
sources  of  protein.  For  the  purposes  of  the  stock  feeder,  there- 
fore, it  still  seems  necessary  to  adhere  to  the  older  method  which 
regards  the  digestible  protein  of  a  feeding  stuff  as  expressing 
approximately  its  production  value  in  this  respect,  thus  vir- 
tually assuming  that  in  ordinary  mixed  rations  the  protein 
deficiencies  of  the  different  ingredients  will  largely  balance  each 
other,  and  this  method  has  been  followed  in  the  tables  of  the 

1  Grindley,  Joseph  and  Slater;  Jour.  Amer.  Chera.  Soc.,  37  (1915),  1778  and 
2762:  Nollau;  Jour.  Biol.  Chem.,  21  (1915),  611. 


THE  PRODUCTION  VALUES  OF   FEEDING  STUFFS     68l 

Appendix.  This  should  be  done,  however,  with  a  distinct 
consciousness  of  the  inadequacy  of  the  method  and  with  the 
hope  that  it  may  ultimately  be  replaced  by  one  having  a  more 
scientific  basis. 

Meanwhile,  notice  should  be  taken  of  the  results  of  several 
recent  investigations  upon  the  mixed  proteins  of  a  few  feeding 
stuffs,  particularly  those  of  the  cereal  grains. 

783.  Low  value  of  maize  proteins.  —  The  demonstration  of 
the  insufficiency  of  the  zein  of  maize  for  either  maintenance 
or  growth  (781)  has  tended  not  unnaturally  to  produce  the 
impression  that  this  important  feeding  stuff  is  relatively 
valueless  as  a  source  of  .protein.  Zein,  however,  is  not  the  only 
protein  of  maize.  According  to  Osborne  and  Mendel 1  the  mixed 
proteins  of  maize  are  made  up  approximately  as  follows :  — 

Zein 41  % 

Maize  glutelin 31  % 

Globulins,  albumins  and  proteoses 22% 

Insoluble  in  alkali 6  % 

100% 

Glutelin  yields  all  the  amino  acids  which  zein  lacks  and 
the  same  is  probably  true  of  the  other  proteins  of  maize.  Evi- 
dently the  results  of  experiments  on  zein  do  not  show  maize 
to  be  valueless  as  a  source  of  protein,  although  they  do  indicate 
a  relatively  low  value  and  this  conclusion  has  been  confirmed  by 
the  experiments  of  Osborne  and  Mendel  on  rats  and  of  Waters 
on  pigs.  On  the  other  hand,  however,  Hart  and  McCollum  2 
were  able  to  obtain  a  normal  growth  of  pigs  on  rations  supply- 
ing only  maize  protein  but  supplemented  by  salts. 

Osborne  and  Mendel l  have  investigated  the  nutritive  value  of  the 
mixture  of  proteins  contained  in  the  "corn  gluten"  produced  in  the 
manufacture  of  starch  from  maize  and  consisting  chiefly  of  zein  and 
glutelin  in  the  proportion  of  approximately  100  to  44.  In  such  a 
mixture,  the  deficiencies  of  the  zein  are  to  a  greater  or  less  extent 
compensated  for  by.  the  glutelin,  and  the  mixed  proteins  not  only 
proved  adequate  for  maintenance  but  were  able  to  support  rather 
slow  growth.  The  addition  to  them  of  lactalbumin  or  of  casein, 
however,  rendered  them  much  more  efficient  and  induced  normal 
growth. 

1  Jour.  Biol.  Chem.,  18  (1914),  i.  2  Ibid.,  19  (1914),  373. 


682 


NUTRITION  OF  FARM  ANIMALS 


Waters  l  in  experiments  on  growing  pigs  has  shown  in  a  striking 
manner  the  practical  significance  of  Osborne  and  Mendel's  results. 
In  each  of  the  four  trials  reported,  one  lot  of  animals  received  only 
maize.  The  others  were  given  maize  with  the  addition  of  ash  in- 
gredients, either  by  direct  additions  of  salts  or  in  the  form  of  the  so- 
called  protein-free  milk,  while  still  others  received  an  addition  of 
complete  proteins,  as  nearly  ash-free  as  possible,  derived  in  some 
cases  from  blood  and  in  others  from  milk.  The  growth  of  the  lots 
receiving  only  maize  was  either  very  slow  or  practically  zero  and  the 
same  was  true  when  ash  was  added,  showing  that  the  failure  to  grow 
was  not  due  to  a  lack  of  mineral  matter.  When,  however,  com- 
plete proteins  were  added  to  the  maize,  steady  and  normal  growth 
took  place  and  comparative  analyses  of  the  carcasses  showed  a  cor- 
responding storage  of  body  protein  by  the  animals.  The  total  re- 
sults as  to  live  weights  were  as  follows :  — 

TABLE  212.  —  INFLUENCE  OF  NATURE  OF  PROTEIN  SUPPLY  ON  GROWTH 

OF  PIGS 


LENGTH  OF 
TRIAL 

INITIAL  z 
WEIGHT 

FINAL 
WEIGHT 

DAILY 
GAIN 

Days 

Lb. 

Lb. 

Lb. 

Second  trial 

Miaize  alone 

280 

CTQ 

1  08 

O.2I 

Maize  and  ash    

280 

Ow 

So 

IO2 

O.I9 

Maize  and  blood  albumin     .     . 

280 

50 

330 

I.OO 

Maize,  blood  albumin  and  ash 

280 

50 

362 

I.  II 

Third  trial 

Miaize  alone 

187 

^o 

CT 

O. 

M^aize  and  ash 

icj/ 
187 

o^ 

CQ 

o  A 

CQ 

o. 

Maize  and  protein-free  milk 

A  °  / 

187 

0  w 

50 

0 

38 

—  0.06 

Maize  and  milk  protein   .     .     . 

187 

50 

334 

1.50 

Fourth  trial 

Maize  alone  

1  80 

50 

117 

0.37 

Maize  and  ash    

1  80 

50 

108 

0.32 

Maize  and  protein-free  milk      . 

1  80 

50 

141 

0.51 

Maize  and  milk  albumin       .     . 

1  80 

50 

239 

1.05 

M^aize  and  casein 

1  80 

co 

2QI 

I  34 

Fifth  trial 

0^ 

^.y  j. 

*  'O^ 

M^aize  alone 

200 

•2Q 

70 

O2^ 

Maize  and  milk  ash     .... 

200 

O^ 

30 

/  y 

55 

w.  ^^ 
0.13 

Maize  and  tryptophan     .     .     . 

200 

30 

74 

O.22 

Maize  and  milk  albumin       .     . 

200 

30 

268 

I.I9 

Maize  and  casein    

200 

30 

232 

I.OI 

1  Proc.  Soc.  Prom.  Agr.  Sci.  (1914),  p.  7. 

2  Approximate.    The  exact  initial  weights  are  not  given  in  the  report  cited. 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    683 

784.  Values  of  other  cereal  proteins.  —  Investigations  at  the 
Wisconsin  Experiment  Station  led  to  the  conclusion  that  not 
only  the  proteins  of  maize  but  the  unbalanced  proteins  of  other 
cereal  grains  are  distinctly  inferior  to  milk  proteins  as  sources 
of  protein  for  growth  and  milk  production. 

Hart,  Humphrey  and  Morrison  1  in  two  comparisons  of  maize  and 
alfalfa  proteins  for  growing  heifers  observed  a  retention  of  approxi- 
mately 20  to  24  per  cent  of  the  maize  nitrogen  as  compared  with 
much  higher  figures  obtained  for  milk  proteins  in  later  experiments 
at  the  same  institution. 

McCollum  2  reports  a  series  of  trials  on  young  pigs  in  which  the 
effects  of  the  proteins  of  maize,  wheat  and  oats,  of  casein  and  of  skim 
milk  on  the  nitrogen  balance  were  compared.  The  protein  supply 
varied  in  the  different  trials  but  the  author  presents  reasons  for  believ- 
ing that  in  no  case  did  it  exceed  the  amount  the  animal  was  capable 
of  utilizing  in  growth,  so  that  the  results  are  not  affected  in  the 
manner  discussed  in  Chapter  XI  (468)  by  surplus  protein  being 
katabolized.  On  the  higher  protein  rations,  from  20  to  34  per  cent 
of  the  resorbed  nitrogen  was  retained  in  the  body  of  the  animal, 
while,  contrary  to  what  would  naturally  be  expected,  the  percentage 
retention  was  decidedly  lower  on  rations  supplying  less  protein. 
The  milk  proteins,  on  the  other  hand,  showed  a  decidedly  higher  per- 
centage retention,  viz.,  for  casein  51  per  cent  and  for  skim  milk  pro- 
teins 66  per  cent. 

Hart  and  Humphrey 3  have  compared  the  proteins  of  maize,  wheat, 
gluten  feed,  oil  meal,  distillers'  grains  and  milk  as  sources  of  protein 
for  milking  cows  (587).  Unfortunately,  the  effects  were  chiefly  on 
the  body  protein,  so  that  the  only  comparison  possible  is  between 
the  algebraic  sums  of  body  protein  and  milk  protein.  Computed  in 
this  way,  the  average  percentage  efficiency  for  three  animals  was, 
for  milk  proteins,  59,  for  maize  40,  for  wheat  36,  for  gluten  feed  45, 
for  oil  meal  61  and  for  distillers'  grains  60. 

785.  Alfalfa  proteins.  —  Hart,  Humphrey  and  Morrison  in 
their    comparisons  of  maize  and  alfalfa   proteins   just   men- 
tioned (784),  found  the  total  nitrogen  of  alfalfa  to  show  about 
the  same  percentage  retention  in  both  growth  and  milk  pro- 
duction as  did  the  total  nitrogen  of  maize. 

In  none  of  these  Wisconsin  experiments  is  the  maintenance 
requirement  of  the  animals  taken  into  account  in  computing 

1  Jour.  Biol.  Chem.,  13  (1912),  133.  2  Ibid.,  19  (1914),  323. 

3  Ibid.,  21  (1915),  239;  26  (1916),  457. 


684  NUTRITION  OF  FARM  ANIMALS 

the  percentage  efficiency  of  the  protein.  If  this  be  done,  using 
the  approximate  data  contained  in  Chapter  IX  (415-417),  the 
percentages  of  the  proteins  supplied  in  excess  of  maintenance 
which  were  retained  would  be  distinctly  increased  in  every  case. 
It  cannot  be  concluded,  therefore,  that  the  low  percentages 
computed  by  the  Wisconsin  investigators  show  that  only  these 
rather  small  proportions  of  the  cereal  proteins  are  capable  of 
transformation  into  body  proteins.  On  the  other  hand,  how- 
ever, such  a  conjectural  correction  would  result  in  making  the 
relative  differences  between  the  different  proteins  appear 
greater  than  those  shown  by  the  method  of  calculation  used. 

No  other  studies  upon  the  relative  values  of  the  mixed  pro- 
teins of  feeding  stuffs  have  come  to  the  writer's  notice. 

Value  of  non-protein 

In  a  previous  paragraph  (782)  the  conclusion  was  reached 
that  for  the  present  the  only  available  measure  of  the  protein 
values  of  feeding  stuffs  is  the  total  amount  of  digestible  pro- 
tein which  they  contain.  In  the  application  of  this  method 
it;  becomes  necessary  to  decide  whether  the  basis  of  compari- 
son shall  be  the  "  crude  "  protein  or  the  "  true  "  protein  as  de- 
termined by  existing  conventional  methods  (104-107) ;  in  other 
words,  to  decide  what  value,  if  any,  shall  be  assigned  to  the 
non-protein. 

786.  Early   investigations.  —  Following   the   recognition   of 
the  fact  that  the  substances  grouped  under  the  collective  term 
non-protein  make  up  a  considerable  share  of  the  nitrogenous 
matter  of  numerous  feeding  stuffs,  much  labor  has  been  ex- 
pended in  efforts  to  determine  their  nutritive  value  as  com- 
pared with  that  of   the  true  proteins.      These  investigations 
have    been    summarized    by    the    writer    elsewhere.1      While 
much  diversity  of  opinion  has  prevailed,  the  general  tendency 
has  been  to  consider  the  non-protein  as  of  questionable  value. 
Kellner,  the  leading  German  authority,  in  particular,  regarded 
it  as  valueless. 

787.  New  viewpoint.  —  With  advancing  knowledge  of   the 
chemistry  of  the  proteins  and  of  the  chemical  mechanism   of 

1  Principles  of  Animal  Nutrition,  pp.  52-58 ;  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus., 
Bui.  139  (1911). 


THE  PRODUCTION   VALUES  OF  FEEDING   STUFFS     685. 

protein  nutrition,  however,  it  has  become  increasingly  evident 
that  many  of  these  earlier  results  are  of  little  real  significance 
and  that  the  question  of  the  nutritive  value  of  non-protein  must 
be  approached  from  a  different  standpoint.  It  has  become 
evident,  for  example,  that  attempts  to  replace  proteins  com- 
pletely by  a  single  amino  acid  or  even  by  two  or  three  of  them 
must  necessarily  fail,  since  the  formation  of  body  protein  re- 
quires the  presence  of  all  its  constituent  building  stones  in 
proper  proportions.  For  the  same  reason  the  addition  of  an 
amino  acid  to  a  ration  can  be  effective  only  if  the  proteins  of 
that  particular  ration  happen  to  be  deficient  in  that  one  con- 
stituent. 

Furthermore,  experiments  with  ingredients  of  the  non-protein 
which  do  not  form  part  of  the  protein  molecule  are  of  question- 
able significance.  For  example,  asparagin,  which  has  been  a 
favorite  subject  of  investigation  for  reasons  of  convenience,  is 
not  found  among  the  cleavage  products  of  the  proteins  but  be- 
longs to  the  class  of  acid  amides.  So  far  as  appears,  it  could 
contribute  to  the  formation  of  protein  only  after  conversion  into 
the  related  aspartic  acid  (47)  and  it  has  not  yet  been  shown 
that  the  body  can  undo  the  amide  linkage' of  nitrogen.  More- 
over, as  appeared  in  Chapter  I  (60-67),  the  non-protein  in- 
cludes, in  addition  to  acid  amides  like  asparagin,  a  great 
variety  of  nitrogenous  substances  which  are  but  remotely  re- 
lated chemically  to  the  proteins  and  whose  nutritive  value  is 
at  best  doubtful. 

It  would  appear  that  the  value  of  the  non-protein  of  a  feeding 
stuff  as  a  source  of  body  protein  must  be  determined  by  pre- 
cisely the  same  thing  which  is  believed  to  measure  the  value  of 
an  individual  protein  or  of  the  mixed  proteins  of  feeding  stuffs, 
viz.,  the  kinds  and  proportions  of  amino  acids  which  it  can 
yield,  since  there  is  no  evident  reason  why  an  amino  acid  ex- 
isting ready  formed  in  a  feeding  stuff  should  differ  in  value  from 
the  same  substance  split  off  from  protein  in  the  process  of  di- 
gestion. If  this  be  admitted,  however,  the  distinction  made  in 
recent  years  between  protein  and  non-protein  in  feeding  stuffs 
becomes  rather  meaningless.  If  the  value  of  each  is  measured  by 
its  amino  acid  content,  then  what  is  needed  to  fix  the  produc- 
tion values  of  feeding  stuffs  as  regards  protein  is  a  knowledge  of 
the  kinds  and  amounts  of  these  compounds  which  the  feeding 


686  NUTRITION  OF  FARM  ANIMALS 

stuff  as  a  whole  (i.e.,  its  crude  protein)  can  furnish,  irrespective 
of  whether  they  exist  in  a  soluble,  as  it  were  predigested,  form  or 
are  first  produced  in  the  digestive  tract  of  the  animal. 

788.  Indirect  utilization  of  non-protein  by  herbivora.  —  In 
the  case  of  herbivora,  especially  of  ruminants,  another  factor 
enters  into  the  consideration  of  the  value  of  the  non-protein, 
viz.,  its  relation  to  the  ferment  organisms  which  play  so  large 
a  part  in  the  digestive  processes  of  these  animals. 

It  was  stated  in  Chapter  III  (141)  that  the  presence  of  soluble 
nitrogenous  compounds  in  the  feed  tends  to  stimulate  the  mul- 
tiplication and  activity  of  these  organisms,  thus  bringing  about 
an  increase  in  the  excretion  of  methane  and  in  the  proportion 
of  carbohydrates  apparently  digested.  It  was  likewise  indicated 
that  the  protein  produced  at  the  expense  of  non-protein  in  the 
multiplication  of  the  microorganisms  might  serve  as  a  source  of 
protein  to  the  body  and  thus  bring  about  an  indirect  utilization 
of  the  non-protein.  Much  experimental  evidence  supporting 
this  view  is  on  record,  particularly  the  extensive  investigations 
of  Morgen  and  his  associates,  which  have  been  discussed  else- 
where 1  by  the  writer.  Three  general  conclusions  regarding 
the  behavior  of  non-protein  in  the  body  were  drawn,  viz. : — 

In  ruminants,  a  conversion  of  non-protein  into  protein  appears 
to  be  effected  by  the  microorganisms  of  the  digestive  tract. 
The  extent  of  this  conversion  appears  to  be  relatively  greater 
in  the  case  of  ammonium  salts  and  asparagin  than  in  that  of 
the  non-protein  of  vegetable  extracts. 

The  protein  thus  formed  from  non-protein  seems  to  be  digested 
subsequently.  The  apparent  formation  of  indigestible  protein 
observed  by  some  investigators  appears  to  be  due  to  an  increase 
in  the  metabolic  products  contained  in  the  feces,  caused  by  the 
specific  action  of  the  vegetable  extracts  upon  the  digestive 
tract. 

By  means  of  its  conversion  into  bacterial  protein,  the  non- 
protein  in  the  feed  of  ruminants  may  serve  indirectly  for  main- 
tenance and  also  as  a  source  of  protein  for  milk,  and  probably 
for  growth,  in  rations  deficient  in  protein. 

Quantitatively,  however,  the  various  forms  of  non-protein 
used  in  these  experiments  were  much  inferior  to  protein  and  a 
substitution  of  the  former  for  the  latter  caused  a  marked  falling 

1  U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.,  Bui.  139  (1911). 


THE  PRODUCTION  VALUES  OF  FEEDING  STUFFS    687 

off  in  production.  For  maintenance  alone,  non-protein  seemed 
quite  effective,  but  neither  for  growth  nor  for  milk  production 
could  it  equal  protein.  It  seems  probable  that  the  limiting 
factor  in  this  indirect  utilization  of  non-protein  is  the  extent  to 
which  it  can  be  synthesized  into  protein  by  the  microorganisms 
rather  than  any  inferiority  in  the  nutritive  value  of  the  result- 
ing protein. 

789.  Conclusions.  —  It  seems  clear  that  the  evidence  is  in- 
sufficient to  warrant  any  general  conclusions  regarding  the  nu- 
tritive value  of  non-protein,  if  indeed  any  general  statement 
regarding  such  a  heterogeneous  group  is  possible.  Ultimately, 
it  may  be  that  studies  of  the  amino  acid  yields  of  the  total  ni- 
trogenous matter  (crude  protein)  of  feeding  stuffs,  or  com- 
parisons of  its  relative  efficiency  in  supporting  maintenance  or 
growth,  will  lead  to  the  formulation  of  production  values  for 
the  crude  proteins  of  different  materials,  but  for  the  present 
the  writer  feels  that  the  safer  course  is  to  make  the  digestible 
"  true  "  protein,  so-called,  the  basis  of  comparison. 

While  some  experiments,  notably  the  Copenhagen  experi- 
ments on  dairy  cows  (586),  seem  to  indicate  a  relatively  high 
value  for  the  non-protein  of  roots  especially,  most  investigators, 
particularly  Morgen  and  his  associates,  have,  as  already  noted, 
found  them  decidedly  inferior  to  protein.  It  is  true  that  the 
non-protein  contains  amino  acids  which  may  at  times  be  utilized 
indirectly  by  herbivora  through  the  agency  of  the  microor- 
ganisms of  the  digestive  tract,  but  even  this  indirect  utilization 
seems  to  be  rather  limited  in  extent  in  most  instances.  The 
conventional  "  true  "  protein,  on  the  other  hand,  may  be  re- 
garded as  representing  approximately  the  real  proteins  of  a 
feeding  stuff  and  it  would  seem  that  these  mixed  proteins  are 
likely  to  supply  more  nearly  a  balanced  amino  acid  mixture  in 
digestion  than  would  result  from  the  inclusion  of  the  non-pro- 
tein. Investigations  of  the  protein  values  of  feeding  stuffs 
should  doubtless  take  account  of  whatever  amino  acids  the 
non-protein  supplies,  i.e.,  they  should  relate  to  the  crude  pro- 
tein. With  continued  study  of  these  relations,  it  may  be  hoped 
that  greater  clarity  may  be  attained,  but  until  that  end  is 
reached,  the  digestible  "  true  "  protein  seems  the  safer  basis 
for  the  formation  of  tables  of  the  production  values  of  feeding 
stuffs  and  for  the  computation  of  rations.  Whatever  error  is 


688  NUTRITION  OF  FARM  ANIMALS 

thus  involved  tends  to  make  the  protein  content  of  the  rations 
somewhat  higher  than  if  the  crude  protein  were  made  the  basis 
of  the  computation.  It  is,  therefore,  an  error  on  the  safe  side, 
since  a  deficiency  of  protein  may  limit  production  while  a  sur- 
plus at  worst  simply  tends  to  increase  the  cost  of  the  ration,  and 
the  difference  in  the  latter  respect  is  seldom  considerable. 


CHAPTER  XVIII 

THE  COMPUTATION  OF  RATIONS 

§  i.  FEEDING  STANDARDS 

790.  Origin.  —  As  the  hay  values  described  in  Chapter  XVI 
(700)  gradually  gave  place  to  new  methods  of  comparing  the 
values  of  feeding  stuffs  based  upon  improved  methods  of  chemi- 
cal analysis  and  upon  investigations  into  the  general  laws  of 
nutrition,  an  attempt  naturally  followed  to  express  the  nutritive 
requirements  of  animals  in  a  similar  manner  instead  of  in  terms 
of  gross  weight  of  feed  or  of  hay  values.     Thus  originated  the 
feeding  standards  for  different  species  of  farm  animals  which 
later  came  to  be  popularly  regarded  more  or  less  in  the  light  of 
prescriptions  or  recipes  for  successful  feeding. 

791.  Early  standards.  —  The  earliest  suggestion  along  this 
line  seems   to   have  originated  with   Haubner J  about    1840. 
Lingethal,1  in  1857,  amplified  the  suggestion,  but  Grouven2in 
1858  was  the  first  to  formulate  specifically  the  requirements 
of   farm    animals,  expressing  them  in    terms  of    dry  matter, 
total  protein,  total  fat  (ether  extract),  and  "  carbohydrates  " 
(total  material  soluble  in  acids  and  alkalies).     In  other  words, 
the  crude  nutrients  were  the  basis  of  Grouven's  standards. 

Wolff  took  the  next  step  in  advance  by  making  the  digestible 
nutrients  as  determined  by  the  methods  of  Henneberg  and 
Stohmann  (707-710)  the  basis  for  comparisons  of  feeding  stuffs 
and  for  expressing  feed  requirements.  His  feeding  standards 
were  first  published  in  1864  in  Mentzel  and  von  Lengerke's 
Landwirtschaf tlicher  Kalender  and  were  also  incorporated  in  his 
widely  read  book,  Die  landwirtschaftliche  Fiitterungslehre,  in 
1874.  These  standards  attempted  to  formulate  the  amounts 
of  digestible  protein,  carbohydrates  and  fats  which  should  be 

Quoted  by  Grouven ;  Kritische  Darstellung  aller  Fiitterungs-Versuche.  Kas- 
sel,  1863,  p.  327. 

2  Vortrage  iiber  Agricultur-Chemie,  1858. 
2  Y  689 


690  NUTRITION  OF  FARM  ANIMALS 

contained  in  rations  for  various  purposes  in  order  to  secure 
satisfactory  results  under  average  conditions.  Thus,  the 
Wolff  standard  for  dairy  cows  was :  — 

FEEDING  STANDARD  FOR  MILK  Cows  PER  DAY  AND  1000  POUNDS  LIVE 

WEIGHT 

Total  dry  matter 24     pounds 

Digestible  protein 2.4  pounds 

Digestible  fat 0.4  pound 

Digestible  carbohydrates 12.5  pounds 

Nutritive  ratio i :  5.4 

This  means  that  any  mixture  of  suitable  feeding  stuffs 
from  which  a  cow  can  digest  2.5  pounds  of  protein  and  13 
pounds  of  non-nitrogenous  nutrients  per  day  will  constitute  a 
suitable  ration  and  produce  a  good  flow  of  milk. 

The  Wolff  standards  were  introduced  into  the  United  States 
a  few  years  later  through  the  writings  of  Johnson,  Atwater 
and  others,  and  by  the  writer's  translation  of  Wolff's  book,1 
and  found  wide  currency  among  students  of  stock  feeding  and 
with  popular  writers. 

792.  Modifications  of  the  Wolff  standards.  —  That  with  the 
progress   of   investigation   modifications   should   be   made   in 
standards  formulated  fifty  years  ago  was  to  be  expected.     From 
1864  to   1896  Wolff's  standards  were  published  annually  in 
Mentzel  and  von  Lengerke's  Kalender  practically  unchanged. 
From  1897  to  1906  they  were  continued  under  the  charge  of 
Lehmann,  who  introduced  some  additions  and  modifications, 
the  principal  ones  being  the  subdivision  of  the  standard  for  dairy 
cows  according  to  milk  yield  and  the  distinction  between  meat 
and  milk  or  wool  breeds  in  the  standards  for  growing  animals. 
These  constitute  the  well  known  Wolff-Lehmann  standards. 

793.  Kellner's  standards.  —  Both  the  Wolff  and  the  Wolff- 
Lehmann  standards,  as  already  noted,  were  expressed  in  terms 
of  the  so-called  digestible  nutrients.     Kellner,  in  1905,  in  the 
first  edition  of  his  Ernahrung  der  landwirtschaftlichen  Nutz- 
tiere,  proposed  the  system  of  calculation  by  means  of  starch 
values  (772)  which  has  since  been  associated  with  his  name, 
and  formulated  a  table  of  feeding  standards  expressed  accord- 
ing to  this  new  method. 

1  Manual  of  Cattle  Feeding,  1880. 


THE  COMPUTATION  OF  RATIONS  691 

In  one  respect  Kellner's  standards  differ  radically  from  pre- 
ceding ones  and  constitute  a  notable  advance.  While  the  earlier 
standards,  like  the  earlier  tables  of  feeding  stuffs,  assume  di- 
gestible protein,  carbohydrates  and  fats  from  different  sources 
to  be  of  substantially  equal  nutritive  value,  Kellner's  figures 
take  account  of  those  differences  in  the  values  of  nutrients  as 
sources  of  energy  which  have  been  revealed  by  recent  inves- 
tigations and  express  the  needs  of  animals  in  this  respect  in 
what  are,  in  fact,  although  not  in  form,  net  energy  values.  In 
addition,  his  standards  regard  only  the  true  protein  as  of 
value  and  they  reduce  somewhat  the  very  high  requirements  of 
fattening  animals  for  protein  as  postulated  by  early  authors. 
In  other  respects,  however,  they  are  on  substantially  the  plan 
of  the  Wolff -Lehmann  standards,  i.e.,  they  are  in  form  pre- 
scriptions or  recipes  for  rations  for  different  purposes. 

§  2.  FEED  REQUIREMENTS 

794.  Limitations  of  feeding  standards.  —  From  the  outset  it 
was  necessary  to  guard  against  misconceptions  arising  from  the 
very  definite  form  in  which  the  feeding  standards  were  pre- 
sented. Their  authors  insisted  from  the  first  that  they  were  in- 
tended as  general  guides  and  not  as  fixed  rules  to  be  rigidly  ad- 
hered to.  But  the  human  mind  craves  a  recipe  and  there  has 
been  a  persistent  tendency  to  substitute  for  the  study  of  the 
principles  of  nutrition  a  series  of  exercises  in  applied  arithmetic. 
Others  again,  perhaps  misled  by  the  name,  have  interpreted  the 
feeding  standards  as  representing  a  physiological  demand  of 
the  animal ;  —  a  sort  of  moral  ideal  in  feeding,  to  be  aimed 
at,  but  concerning  which  concessions  have  to  be  made  to  human 
fallibility  and  the  pressure  of  circumstances. 

The  difficulty  inherent,  more  or  less,  in  all  forms  of  feeding 
standards,  but  especially  in  the  earlier  ones,  is  that  they  fail 
to  take  sufficient  account  of  the  fact  that  the  feeding  of  farm 
animals  is  an  economic  problem.  A  manufacturer  would  not 
buy  some  average  amount  of  raw  material  which  might  be  re- 
garded as  the  norm  for  his  business,  irrespective  of  the  capacity 
of  his  own  factory  or  of  the  market  for  the  finished  product. 
When  high  prices  prevailed  he  might  find  it  profitable  to  han- 
dle a  maximum  amount  of  raw  material  and  so  to  reduce  the 


692  NUTRITION   OF  FARM  ANIMALS 

percentage  of  his  overhead  costs,  even  at  the  risk  of  some  loss 
of  efficiency  in  the  manufacturing  process.  In  the  contrary  case, 
he  might  find  it  necessary  to  run  considerably  below  his  max- 
imum capacity  in  order  to  tide  over  a  bad  season.  In  somewhat 
similar  fashion  it  is  necessary  for  the  stock  feeder  to  adapt  his 
rations  to  the  economic  conditions  under  which  he  works.  While 
the  animal  cannot  be  handled  like  a  machine  in  a  factory,  never- 
theless, as  has  appeared  in  previous  chapters,  it  shows  a  large 
degree  of  flexibility  in  its  requirements  both  quantitatively  and 
qualitatively.  No  single  fixed  standard  is  either  physiologically 
or  economically  necessary  for  productive  feeding. 

795.  The  feeder's  problem.  —  As  the  feeder  looks  at  his 
animals,  the  problem  which  they  present  is  a  threefold  one. 

First,  he  must  furnish  them  with  sufficient  repair  material 
and  energy  to  keep  the  body  machinery  running,  i.e.,  he  must 
supply  a  maintenance  ration.  The  requirements  for  this  pur- 
pose, although  subject  to  individual  variations,  have  been 
worked  out  with  some  degree  of  accuracy  and  this  part  of  his 
problem  is  relatively  simple. 

Second,  in  addition  to  a  maintenance  ration,  he  must  supply 
his  animals  with  the  amounts  of  matter  and  of  energy  necessary 
for  the  production  of  the  meat,  milk  or  work  which  he  desires 
them  to  yield.  Here  his  task  is  much  less  simple. 

It  is  evident  in  the  first  place,  as  has  been  emphasized  in 
previous  chapters,  that  the  producing  capacity  of  the  animal 
is  the  prime  factor  in  the  problem.  No  argument  is  necessary 
to  show  that  a  cow  producing  thirty  pounds  of  milk  daily  re- 
quires a  greater  addition  to  her  maintenance  ration  than  does 
one  having  a  capacity  of  only  fifteen  pounds,  or  that  a  steer 
which  can  gain  three  pounds  daily  needs  more  surplus  feed  than 
one  capable  of  making  only  one  pound  of  gain.  Good  business 
economy  demands  that  the  better  animal  be  given  feed  sufficient 
in  amount  and  kind  to  permit  its  producing  capacity  to  be 
fully  utilized,  thus  reducing  the  relative  cost  of  maintenance. 
On  the  other  hand,  it  would  be  an  obvious  waste  to  give  a 
mediocre  or  poor  producer  a  ration  adequate  for  two  or  three 
times  the  production  of  which  it  is  capable. 

Third,  the  feeder,  like  the  manufacturer,  must  adapt  his  prac- 
tice to  market  conditions.  As  prices  of  feeding  stuffs  fall  and 
those  of  animal  products  rise,  he  will  tend  to  feed  more  in- 


THE   COMPUTATION  OF  RATIONS  693 

tensively,  but  here  he  encounters  the  law  of  diminishing  re- 
turns. The  dairy  cow  affords,  perhaps,  the  most  striking  il- 
lustration of  this.  An  increase  in  the  quantity  of  her  feed  above 
a  moderate  ration  may  be  expected  to  cause  an  increase  in  milk 
secretion  but  at  the  same  time  an  increasing  proportion  of  the 
extra  feed  will  be  diverted  to  fattening  (606-610).  Similarly, 
a  rather  small  protein  supply  appears  adequate  to  support  mod- 
erate milk  production  but  larger  amounts  seem  to  act  as  a  stim- 
ulus to  the  activity  of  the  milk  glands  and  to  increase  the  yield 
of  milk  (603),  but  presumably  at  a  diminishing  rate.  The  dairy- 
man's problem  is  to  utilize  these  stimulating  effects  up  to  the 
point  at  which  the  increase  in  yield  is  offset  by  the  added  cost 
of  the  ration,  and  the  solution  of  this  problem  requires  ex- 
perience and  good  judgment  and  is  one  in  which  little  aid  can 
be  afforded  by  feeding  standards. 

What  is  so  emphatically  true  of  dairy  feeding  applies  in 
greater  or  less  degree  to  all  forms  of  animal  production.  Even 
though  there  may  be  no  decrease  in  the  utilization  of  the 
feed  in  the  strict  physiological  sense,  diminished  digestibility, 
stimulation  of  incidental  bodily  activity,  or  changing  com- 
position of  increase  tend  to  make  heavy  rations  or  high 
protein  rations  relatively  less  effective  than  more  moderate 
ones. 

What  the  feeder  needs  in  order  to  meet  this  situation  intel- 
ligently is  not  so  much  a  fixed  standard,  or  group  of  standards,  as 
a  knowledge  of  the  amount  and  kind  of  feed  required  under 
various  conditions  for  the  manufacture  of  a  unit  of  product — 
a  pound  of  increase  in  live  weight,  for  example,  or  a  pound  of 
milk  of  a  given  quality.  To  the  extent  to  which  this  infor- 
mation is  available  he  can,  knowing  his  animals,  proportion 
the  feed  to  the  capacity  of  each  and  thus  go  far  toward  securing 
the  most  efficient  production.  It  appears  desirable,  therefore, 
to  assume  a  somewhat  different  point  of  view  from  that  which 
has  largely  prevailed  in  the  past  and  to  substitute  for  the  con- 
ception of  feeding  standards  the  modified  conception  of  feed 
requirements. 

796.  Feed  requirements.  —  Haecker  l  appears  to  have  been 
the  first  to  apply  this  idea  to  milk  production  and  to  formulate 
the  feed  requirements  for  the  production  of  a  pound  of  milk 
/  l  Minn.  Expt.  Sta.,  Bui.  79  (1903),  pp.  104-107. 


694  NUTRITION  OF  FARM  ANIMALS 

of  different  grades.  As  modified  by  his  subsequent  experiments, 
this  statement  of  requirements  1  has  become  known  as  the 
Haecker  standard,  although,  strictly  speaking,  it  is  not  a 
standard  in  the  older  sense.  The  writer  2  subsequently  pub- 
lished a  tentative  statement  of  the  protein  and  energy  require- 
ments per  pound  of  milk  containing  four  per  cent  of  fat  and 
illustrated  the  computation  of  rations  on  this  basis,  without, 
however,  attempting  similar  estimates  for  other  grades  of 
milk.  Later  Woll  and  Humphrey,3  Savage 4  and  Eckles 5 
have  adopted  various  forms  of  the  same  conception.  Henry 
and  Morrison  6  have  included  in  their  modified  Wolff-Lehmann 
standards  Haecker's  requirements  for  milk  production  and 
also  similar  data,  based  on  unpublished  results  by  the  same 
experimenter,  for  growing  fattening  steers,  and  have  also 
widened  somewhat  the  range  of  the  standards  for  other  pur- 
poses and  introduced  minimum  and  maximum  figures. 

On  the  other  hand,  however,  all  of  the  foregoing  requirements 
and  standards,  with  the  exception  of  Eckles',  are  expressed  in 
terms  of  digestible  nutrients  and  are  therefore  open  to  the 
criticism  of  ignoring  differences  in  the  relative  values  of  nu- 
trients from  different  sources. 

797.  Requirements  in  terms  of  protein  and  energy.  — 
The  several  chapters  of  Part  III  were  devoted  primarily  to  a 
consideration  of  the  feed  requirements  of  farm  animals  in 
terms  of  digestible  protein  and  of  net  energy.  In  the  case  of 
maintenance,  these  requirements  may  be  regarded  as  to  a  cer- 
tain degree  fixed  and  capable  of  computation  upon  the  basis 
of  the  size  of  the  animal,  being  related  either  to  its  weight  or 
to  its  body  surface.  In  the  case  of  productive  feeding,  on  the 
contrary,  the  obvious  method  of  comparison  is  that  of  feed 
(in  excess  of  maintenance)  with  yield,  and  an  attempt  was 
therefore  made  to  estimate  the  feed  requirements  per  unit  of 
product.  The  results  of  these  estimates  have  been  brought 
together  in  Tables  I- VI  of  the  Appendix,  which  include  also  for 
convenience  estimates  of  the  total  requirements  per  day  and 
head  for  normal  growth  at  different  weights  and  ages. 

1  Minn.  Expt.  Sta.,  Bui.  140,  p.  56. 

J  U.  S.  Dept.  Agr.,  Farmers'  Bui.  346  (1909),  pp.  19-25. 

3  Wis.  Expt.  Sta.,  Research  Bui.  13.  4  N.  Y.  (Cornell)  Expt.  Sta.,  Bui.  323. 

6  Mo.  Expt.  Sta.,  Research  Bui.  7.  6  Feeds  and  Feeding,  isth  Ed.,  p.  669. 


THE   COMPUTATION  OF  RATIONS  695 

That  the  requirements  there  tabulated  resemble  more  or  less 
the  earlier  feeding  standards  and  share  to  some  degree  their 
limitations  is  undeniable  and  likewise  unavoidable.  No  finite 
number  of  formulas,  however  accurate,  can  cover  specifically 
all  the  various  conditions  of  practice,  and  in  particular  it  is 
scarcely  possible  for  them  to  include  any  consideration  of  the 
financial  aspects  of  the  matter.  The  most  that  seems  possible 
is,  first,  to  formulate  the  average  requirements  under  ordinary 
circumstances  and  then  to  indicate  as  definitely  as  present 
knowledge  permits,  as  has  been  attempted  in  Chapters  VII- 
XIV,  the  influence  of  various  conditions  in  modifying  these 
requirements.  The  difference  between  the  older  and  newer 
formulas  lies  far  more  in  the  point  of  view  than  in  the  com- 
pleteness or  exact  numerical  accuracy  of  the  figures  and  neither 
can  be  utilized  as  infallible  recipes  which  shall  spare  the  user 
the  trouble  of  observing  and  thinking. 

798.  Defects  of  the  tables.  —  That  not  a  few  of  the  estimates 
of  feed  requirements  contained  in  the  Tables  of  the  Appendix 
rest  on  quite  meager  data  is  apparent  from  the  discussions  in 
Part  III.  This  is  particularly  true  of  the  requirements  for 
growth,  as  will  be  evident  from  a  study  of  Chapter  XI.  To  a 
somewhat  less  degree  the  same  is  true  of  those  for  milk  pro- 
duction, the  energy  requirements  in  particular  being  based  on 
an  hypothesis  regarding  the  cause  of  the  higher  net  energy 
values  for  milk  production  (593,  605)  which  has  not  yet  been 
submitted  to  experimental  test. 

The  estimates  of  the  protein  requirements  are  particularly 
unsatisfactory  for  two  reasons. 

In  the  first  place,  they  virtually  assume  all  proteins  to  be  of 
equal  value.  That  such  is  not  the  case  has  been  repeatedly 
stated  in  previous  pages,  but  it  has  also  been  shown  that 
present  knowledge  of  the  constitution  of  the  vegetable  proteins 
and  of  the  amino  acid  requirements  of  the  body  is  insuffi- 
cient to  serve  as  the  basis  of  a  more  satisfactory  system. 

In  the  second  place,  there  has  been  very  little  systematic 
investigation  of  the  minimum  protein  requirements  of  farm 
animals  for  different  purposes  or  of  the  percentage  of  different 
proteins  capable  of  utilization  for  the  production  of  body  pro- 
tein or  of  milk  protein.  The  requirements  given  in  the 
tables  are,  to  a  large  extent,  based  on  observations  in  practice, 


696  NUTRITION  OF  FARM  ANIMALS 

and  it  is  quite  possible  that  they  may,  with  safety,  be  con- 
siderably reduced  in  some  instances. 

Furthermore,  the  tables  of  the  Appendix  include  no  esti- 
mates of  the  ash  requirements.  This  is  not  because  the 
latter  are  unimportant,  for  it  is  not  improbable  that  they  may 
at  times  be  a  controlling  factor,  but  simply  because  study 
in  this  field  has  not  progressed  far  enough  to  permit  of  their 
formulation. 

But  while  it  has  seemed  desirable  to  emphasize  here  certain 
defects  of  the  feeding  requirements  as  formulated,  as  a  pre- 
caution against  their  uncritical  use,  they  are  by  no  means  to 
be  rejected  as  worthless  but  are  capable  of  affording  valuable 
aid  to  the  intelligent  feeder.  By  their  use  he  can  get  a  general 
idea  of  the  feed  requirements  of  his  animals  and  can  compute 
rations  which  will  approximately  supply  the  requisite  amounts 
of  protein  and  energy.  His  ability  as  a  feeder  will  be  shown, 
first,  in  his  power  to  estimate  the  conditions  which  will  modify 
the  feed  requirements  of  his  particular  animals  and  cause  his 
feeds  to  vary  from  the  average,  and  second,  in  the  skill  with 
which  he  can  interpret  the  daily  results  and  modify  his  feeding 
in  accordance  with  them. 

799.  Dry  matter.  —  The  amount  of  dry  matter  which  the 
ration  contains  must  also  be  taken  into  consideration.  The 
total  volume  of  feed  which  an  animal  requires,  although  rather 
variable,  has  its  limits.  In  computing  rations  the  most  con- 
venient indication  of  the  bulk  of  the  feeds  is  the  percentage  of 
dry  matter  shown  in  the  first  column  of  Tables  VII,  VIII  and 
IX  of  the  Appendix.  In  very  general  terms  it  may  be  said 
that  a  looo-pound  ruminant  should  be  given  from  20  to  30 
pounds  of  dry  matter  per  day,  25  pounds  being  perhaps  a 
fair  average,  while  for  the  horse  smaller  amounts  will  be 
appropriate. 

An  examination  of  the  tables  shows  that  concentrated  feed- 
ing stuffs  contain  much  more  protein  and  energy  in  proportion 
to  their  dry  matter  than  do  the  forage  crops.  Evidently,  then, 
in  heavy  feeding,  where  the  purpose  is  to  give  the  animal  all  the 
feed  possible,  the  ration  should  consist  as  largely  as  practicable 
of  concentrated  feeding  stuffs,  because  only  in  that  way  can  the 
required  amount  of  nutriment  be  obtained  without  unduly  in- 
creasing the  bulk  of  the  ration.  In  light  feeding,  on  the  contrary, 


THE   COMPUTATION  OF  RATIONS  697 

roughage  may  predominate,  because  it  is  usually  relatively 
cheaper  and  can  supply  the  required  amount  of  feed  in  a  bulk 
which  the  animal  can  consume. 


§  3.  METHOD  OF  COMPUTATION  l 

The  examples  given  on  the  following  pages  are  intended  simply 
as  illustrations  of  the  method  of  using  the  tables  of  the  Appendix 
and  not  as  model  rations.  Limitations  of  space  forbid  the 
multiplication  of  examples,  but  the  reader  who  grasps  the 
method  will  have  no  serious  difficulty  in  applying  it  to  his 
own  conditions,  while  facility  will  be  acquired  with  surprising 
rapidity  by  practice.  It  will  be  observed  that  the  form  of 
these  tables  and  the  methods  of  computation  do  not  differ 
materially  from  those  which  have  been  used  for  many  years  in 
computing  rations  on  the  basis  of  "  digestible  nutrients,"  al- 
though the  significance  of  some  of  the  figures  is  different.  It 
may  be  added  that  the  digestible  protein  in  the  tables  is  true 
protein  —  that  is,  it  does  not  include  the  non-protein. 
Consequently  the  percentages,  as  well  as  the  amounts  esti- 
mated in  the  rations  on  succeeding  pages,  are  somewhat 
smaller  than  in  the  older  tables. 

800.  Total  feed  required.  —  A  bunch  of  "  feeders  "  2  to  3 
years  old,  averaging  1000  pounds  per  head  and  in  better  than 
average  condition  are  to  be  fattened  on  clover  hay  and  corn- 
and-cob  meal.  Such  cattle,  if  of  good  grade,  should  weigh 
1400  pounds  each  when  ready  for  market  and  should  not  re- 
quire over  200  days  to  make  the  gain  of  400  pounds.  They 
should  therefore  make  an  average  gain  of  2  pounds  per  day. 

It  may  be  estimated  (Table  III)  that  a  gain  of  i  pound  live 
weight,  by  animals  of  this  grade  will  require  about  3.5  Therms 
of  net  energy  value  in  the  feed ;  for  a  daily  gain  of  2  pounds, 
therefore,  the  requirement  would  be  7  Therms.  To  this  must  be 
added  the  maintenance  requirement,  which  will  increase  as  the 
animals  grow  heavier.  For  the  average  weight  of  1200  pounds 
it  is  sufficiently  accurate  to  use  the  maintenance  requirement 
computed  (Table  I)  for  1250  pounds,  viz.,  7  Therms.  This 

1  The  contents  of  this  section  are  reproduced  by  permission  of  the  Honorable 
Secretary  of  Agriculture,  from  Bulletin  No.  459  of  the  U.  S.  Department  of  Agri- 
culture, prepared  by  the  writer. 


698 


NUTRITION  OF  FARM  ANIMALS 


makes  the  total  net  energy  requirement  per  day  14  Therms  on 
the  average  of  the  whole  feeding  period. 

If  we  assume  that  2  pounds  of  grain  will  be  fed  for  each  pound 
of  hay,  it  is  easy  to  compute  from  the  figures  in  the  last  column 
of  Table  VII  the  amount  of  feed  required  to  supply  14  Therms 
of  net  energy,  as  follows :  — 

THERMS 

In  TOO  pounds  of  average  clover  hay 38.68 

In  200  pounds  of  corn-and-cob  meal 151.60 

In  300  pounds  of  feed 190.28 

In  i  pound  of  feed 634 

To  supply  14  Therms  requires  14  -f-  0.634  =  22.08  pounds 
of  total  feed,  consisting  of  7.36  pounds  of  clover  hay  and  14.72 
pounds  of  corn-and-cob  meal,  or,  in  round  numbers,  7^  pounds 
of  hay  and  15  pounds  of  meal. 

This,  of  course,  represents  the  average  ration  for  the  whole 
feeding  period.  At  the  beginning  the  feed  will  naturally  be 
lighter  and  consist  to  a  larger  extent  of  hay,  while  the  amount 
of  feed,  and  especially  the  proportion  of  grain,  will  be  gradually 
increased  until,  toward  the  end  of  the  feeding,  the  animals  are 
consuming  all  the  grain  they  will  take,  with  only  enough  hay  to 
insure  the  necessary  bulk  and  proper  digestion.  Naturally, 
too,  the  form  in  which  the  corn  is  given  will  usually  be  varied 
in  the  course  of  the  feeding. 

801.  Improvement  of  a  ration.  —  In  the  foregoing  example 
it  was  assumed  that  the  feeding  stuffs  to  be  used  had  been 
decided  upon  and  attention  was  directed  simply  to  the  quantity 
required.  Let  us  now  take  up  the  question  from  the  other  end 
and  see  whether  a  study  of  the  ration  may  not  yield  some 
suggestion  of  possible  improvement. 

According  to  Table  VII,  clover  hay  and  corn-and-cob  meal, 
respectively,  contain  in  100  pounds :  — 


TOTAL   DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Pounds 

Pounds 

Therms 

Clover  hay   
Corn-and-cob  meal     

87.1 
89.6 

4-9 

5-7 

38.68 
75.80 

THE   COMPUTATION  OF  RATIONS 


699 


The  7^  pounds  of  clover  hay  in  the  ration  will  evidently 
contain :  — 

87.1     X  0.075  =  6.53  pounds  of  dry  matter. 
4.9     X  0.075  =  o-37  pound  of  digestible  protein. 
38.68  X  0.075  =  2-9°  Therms  of  net  energy  value. 

A  precisely  similar  computation  for  the  corn-and-cob  meal 
gives  the  following  results :  - 

89.6    X  0.15    =  13.44  pounds  of  dry  matter. 

5.7     X  0.15    =    0.85  pound  of  digestible  protein. 
75.8     X  0.15     =11.37  Therms  of  net  energy. 

Adding  these  amounts,  we  find  that  the  total  ration  contains : 


TOTAL   DRY 
MATTER 

DIGESTIBLE 
PROTEIN 
\ 

NET 
ENERGY 
VALUE 

Clover  hay,  i\  pounds    
Corn-and-cob  meal,  15  pounds     .... 

Pounds 

6-53 
13-44 

Pounds 

o-37 
•85 

Therms 
2.90 
H-37 

Total     .     . 

IQ  07 

I  22 

IA  27 

The  quantity  of  energy,  of  course,  corresponds  with  that 
estimated  to  be  necessary,  because  the  amounts  of  feed  were 
fixed  upon  on  that  basis.  We  observe,  however,  that  the 
amount  of  digestible  protein  in  the  ration  is  less  than  that 
estimated  in  Table  IV  to  be  needed  by  beef  cattle  of  this  age 
and  weight.  A  ration  like  the  above  might  produce  fair  gains, 
but  it  probably  would  fail  to  take  full  advantage  of  the  capac- 
ity of  such  cattle  for  growth  and  the  gain  would  most  likely 
fall  below  that  which  was  anticipated.  An  increase  in  the  pro- 
tein might  be  expected  to  make  the  ration  more  efficient. 

To  make  any  marked  change  in  the  ration  in  this  respect,  it 
is  evident  that  we  must  introduce  into  it  some  feed  much  richer 
in  protein  than  either  of  those  composing  it.  On  consulting 
Table  VII  it  is  evident  that  what  we  need  is  one  of  the  by-prod- 
uct feeds,  like  gluten  feed  or  meal,  the  oil  meals,  etc.,  and  also 
that  only  a  small  amount  of  one  of  these  will  be  needed  to  effect 
a  marked  change  in  the  ration.  Thus,  if  we  substitute  2  pounds 
of  old-process  linseed  meal  for  2  pounds  of  the  corn-and-cob 
meal,  the  ration  will  foot  up  as  follows :  — 


700 


NUTRITION  OF  FARM  ANIMALS 


TOTAL   DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Clover  hay,  7!  pounds   
Corn-and-cob  meal,  13  pounds     .... 
Old-process  linseed  meal,  2  pounds  .     .     . 
Total     

Pounds 

6-53 
11.65 
1.82 

Pounds 
0-37 
•74 
•57 

Therms 
2.90 

9-85 
1.78 

20.00 

1.68 

14-53 

Thus  at  a  comparatively  small  additional  expense  we  are 
able  to  improve  the  ration  materially  by  adding  the  lacking 
protein,  and  there  is  little  doubt  that  the  improved  ration  would 
produce  a  more  rapid  gain  and,  under  ordinary  conditions,  a 
more  profitable  one  as  well,  either  by  increasing  the  total  gain 
or  shortening  the  feeding  period. 

802.  Computing  a  ration  from  given  feeding  stuffs.  —  There 
are  available  for  a  dairy  herd  field-cured  corn  forage  (including 
the  ears),  clover  hay,  corn  meal,  wheat  bran  and  gluten  feed. 
Table  VII  shows  that  these  feeding  stuffs,  if  of  good  average 
quality,  will  furnish  in  100  pounds :  — 


TOTAL 
DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Corn  forage       
Clover  hay   . 

Pounds 
81.7 
87  I 

Pounds 
2-3 

A    Q 

Therms 

43-94 
^8  68 

Corn  meal    

88.7 

6.4 

8^.20 

Wheat  bran 

80  Q 

10  8 

r  -2  00 

Gluten  meal      ...                        . 

OO  Q 

28  i 

84  ic 

The  cows  average  850  pounds  per  head  and  have  produced  in 
previous  years  an  average  of  20  pounds  of  milk  per  day  testing 
4  per  cent  of  fat.  According  to  Table  I,  the  maintenance 
requirement  of  such  animals  per  day  and  head  would  be 
approximately :  — 


Digestible  protein 0.43  pound 

Net  energy 5.40  Therms 


THE   COMPUTATION  OF  RATIONS 


701 


For  the  production  of  20  pounds  of  4  per  cent  milk  there  would 
be  needed,  according  to  Table  V :  — 

Digestible  protein  (0.05  X  20)    .    .     .     .     i.o  pound 
Net  energy  (0.27  X  20) 5.4  Therms 

The  total  feed  requirements  per  day  and  head  are  therefore : 


DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

For  maintenance                     .                 •                • 

Pounds 

O  A3 

Therms 
54.O 

For  milk  production      

I.OO 

5-40 

Total    

1.4.3 

10.80 

The  problem,  then,  is  to  find  a  mixture  of  the  available  feed- 
ing stuffs  which  will  yield  these  amounts  of  digestible  protein 
and  of  energy,  and  which  shall  have  a  suitable  bulk. 

The  first  step  in  the  construction  of  a  ration  is  to  fix  upon  the 
amounts  of  coarse  fodders.  It  is  usually  desirable  to  use  as 
large  a  proportion  of  these  as  possible,  since  they  are  usually 
cheaper  sources  of  feed  than  grain.  On  the  other  hand,  the 
amount  of  them  which  an  animal  can  consume  is  limited.  Much 
depends  upon  the  individual  animals,  and  the  proper  amount 
can  only  be  told  by  trial,  but  we  should  probably  aim  to  get 
from  12  to  14  pounds  of  dry  matter  in  the  form  of  coarse  fodder. 
Corn  forage  being  a  cheap  feeding  stuff,  we  shall  naturally  use 
this  freely,  with  probably  some  hay  for  variety.  By  a  little 
trial,  we  find  that  10  pounds  of  corn  forage  and  6  pounds  of  clover 
hay  will  give  us  13.4  pounds  of  dry  matter  and  the  amounts  of 
digestible  protein  and  of  energy  shown  below :  — 


TOTAL 
DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Corn  forage 
Clover  hay, 

,  10  pounds       
6  pounds     

Pounds 
8.17 
5-23 

Pounds 
0.23 
.29 

Therms 

4-39 
2.32 

Total 

I3.4-O 

,C2 

6.71 

702 


NUTRITION  OF  FARM  ANIMALS 


To  this  we  have  to  add  sufficient  grain  to  bring  the  ration  up 
to  the  requirement.  The  proper  amount  we  must  ascertain  by 
trial.  We  will  take,  at  a  venture,  4  pounds  of  corn  meal  and 
2  pounds  of  wheat  bran.  Adding  this  to  the  ration  we  have  :  — 


TOTAL 
DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Corn  forage  10  pounds 

Pounds 

o  T7 

Pounds 
O  23 

Therms 

Clover  hay,  6  pounds  ....... 
Corn  meal,  4  pounds  
\Vheat  bran  2  pounds 

0.17 

5.23 

3-55 

T  8n 

.29 
.26 
22 

•6y 

2.32 

3-41 
I  06 

Total     

18-75 

1.  00 

11.18 

Comparing  these  totals  with  the  requirement  as  computed, 
we  find  that  the  ration  is  ample  as  regards  energy,  but  consid- 
erably low  in  digestible  protein.  The  rather  low  figure  for  dry 
matter  shows  that  more  feed  may  be  added  to  the  ration  if 
desirable,  but  the  total  for  net  energy  makes  it  evident  that  what 
is  needed  is  not  more  feed,  but  feed  of  a  different  composition, 
supplying  more  protein  along  with  rather  less  energy.  Gluten 
meal  answers  this  requirement,  and  substituting  2  pounds  of 
it  for  2  pounds  of  corn  meal  gives  a  ration  which,  while  still  a 
trifle  high  in  energy,  agrees  as  closely  as  necessary  with  the 
computed  requirements.  Thus :  — 


TOTAL 
DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Corn  forage,  10  pounds  
Clover  hay,  6  pounds  
Corn  meal,  2  pounds  
Wheat  bran,  2  pounds  
Gluten  meal,  2  pounds  

Pounds 
8.17 
5-23 
1.77 
1.  80 
1.82 

Pounds 
0.23 
.29 
•13 

.22 
•56 

Therms 
4-39 
2.32 
1.70 
1.  06 
1.68 

Total 

l8  7Q 

I  4.^ 

II  It 

This  ration  corresponds  with  the  average  requirement  of  the 
whole  herd,  since  it  is  based  on  its  average  performance.  It 
hardly  need  be  said  that  it  should  be  modified  to  suit  the  re- 
quirements and  capacities  of  the  individual  cows,  the  heavy 
milkers  getting  more  and  the  lighter  ones  less. 


THE  COMPUTATION  OF  RATIONS    .  703 

By  proceeding  in  this  manner,  with  a  little  patience  we  can 
usually  get  a  ration  corresponding  as  closely  as  is  necessary  to 
the  requirement,  provided  the  feeds  available  admit  of  it.  With 
a  little  experience  one  very  soon  learns  to  guess  pretty  closely, 
and  with  some  practice  the  computations  become  very  easy. 
An  exact  agreement  with  the  requirement  need  not  be  sought 
for,  since  in  practice  the  composition  of  the  feeds  will  probably 
vary  more  or  less  from  the  average  of  the  tables. 

803.  The  choice  of  feeding  stuffs.  —  When,  as  in  the  last 
example,  feeding  stuffs  must  be  purchased  in  order  to  get  the 
desired  relation  between  the  protein  and  the  energy  of  the 
ration,  it  is  evident  that  often  a  wide  range  of  choice  may  be 
offered.  In  such  a  case  the  question  at  once  arises  which  of 
the  various  feeds  available  is  it  most  economical  to  purchase,  it 
being  evident,  of  course,  that  this  is  not  necessarily  the  one 
offered  at  the  lowest  price. 

No  simple  method  of  determining  this  point  is  possible,  be- 
cause, as  we  have  seen,  the  food  serves  two  entirely  distinct 
purposes  in  the  body.  Sometimes  the  supply  of  protein  is  the 
specially  important  point,  and  in  other  cases  what  is  needed 
is  a  supply  of  energy  without  special  reference  to  whether  its 
source  be  protein  or  non-nitrogenous  material.  Consequently, 
the  relative  values  of  two  feeding  stuffs  may  vary  under  differ- 
ent circumstances.  Some  writers  have  based  their  compari- 
sons of  the  values  of  by-product  feeds  solely  upon  their  con- 
tent of  protein,  for  the  reason  that  such  feeds  are  often  bought 
especially  to  supply  this  ingredient  while  the  fats  and  es- 
pecially the  carbohydrates  are  usually  produced  in  abundance 
upon  the  farm.  They  regard  that  purchased  feeding  stuff  as 
the  most  economical  which  furnishes  a  pound  of  digestible  pro- 
tein at  the  lowest  cost,  ignoring  any  value  in  the  other  ingre- 
dients. It  is  obvious,  however,  that  this  is  a  one-sided  view. 
The  other  ingredients  have  a  value,  and  this  is  especially  true 
in  the  case  of  a  feeder  who  buys  a  considerable  part  of  his  grain 
supply  and  depends  upon  it  as  a  source  of  energy  as  well  as  of 
protein.  The  method  of  comparison  illustrated  in  the  following 
pages  is  based  primarily  upon  the  cost  per  unit  of  energy  because 
this  is  on  the  whole  the  most  important  function  of  the  feed, 
but  the  method  takes  account  also  of  the  amount  of  protein 
present. 


7°4 


NUTRITION   OF   FARM  ANIMALS 


Let  us  suppose  the  following  feeding  stuffs  are  available  to 
a  dairyman  at  the  prices  named :  — 

Prices  of  feeds  per  ton 

Oats  (40  cents  per  bushel) $25 

Corn  meal       25 

Wheat  bran 21 

Wheat  middlings  (flour) 24 

Dried  brewers'  grains 23 

Gluten  meal 27 

Cotton  seed  meal  (prime) 30 

Old-process  linseed  meal 33 

The  supply  of  coarse  feed  on  the  farm  is  sufficient  to  furnish 
each  animal  per  day  32  pounds  of  silage  and  8  pounds  of  clover 
hay ;  the  cows  average  1000  pounds  each  and  may  be  expected 
to  produce  per  day  about  24  pounds  of  milk  testing  4.5  per  cent 
fat. 

The  first  step  is  to  compute,  in  precisely  the  same  way  as  in  the 
previous  example,  the  estimated  requirements  of  these  cows 
per  day  as  follows :  — 


DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

For  maintenance 

Pounds 

O  "\O 

Therms 
6  oo 

For  24  pounds  of  milk  : 
Protein  24  X  0.052    

I  2$ 

Net  energy  24  X  0.29     

6.96 

Total  requirement       

1-75 

12.96    • 

The  amount  of  silage  and  clover  hay  available  will  furnish, 
according  to  Table  VII,  the  following  amounts  of  dry  matter, 
digestible  protein,  and  net  energy  value  :  — 


TOTAL 
DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Corn  silage 

32  pounds 

Pounds 
8  4.2 

Pound 

O.IO 

Therms 
^.oo 

Clover  hay, 

8  pounds      

6.97 

•39 

3-OQ 

Total    . 

I<.3Q 

.58 

8.18 

THE  COMPUTATION  OF  RATIONS 


705 


The  question  now  is  what  feeding  stuffs  is  it  most  economical 
to  buy  (or  to  refrain  from  selling  if  in  stock)  to  complete  the 
ration.  The  first  step  in  deciding  this  question  is  to  compare 
the  various  feeds  as  sources  of  energy  and  see  which  one  fur- 
nishes a  unit  of  net  energy  value  at  the  lowest  price.  This 
computation  gives  the  following  results :  — 


» 

COST  OF 

100 

POUNDS 

ENERGY 
VALUE  OF 

100 

POUNDS 

COST  OF  i 
THERM 
NET 
ENERGY 
VALUE 

Oats    

$      2* 

Therms 
6?  d6 

Cents 
8* 

Corn  meal    
Wheat  bran 

•25 

Q? 

88.75 

r  -2  OO 

.41 
08 

Wheat  middlings  

2O 

7  S  O2 

60 

Dried  brewers'  grains     ........ 
Gluten  meal      ...          . 

•15 

•2  r 

53-38 
84  ic 

•15 
60 

Cottonseed  meal    
Old-process  linseed  meal 

1.50 

i  6s 

90.00 
88  91 

.67 

86 

Evidently,  if  it  were  simply  a  question  of  supplying  energy  to 
the  animals,  we  should  use  corn  meal,  since  that  supplies  a  unit 
of  energy  at  a  much  lower  price  than  any  of  the  other  feeding 
stuffs.  If  it  were  thought  desirable  to  add  variety  to  the  ration, 
wheat  middlings  would  obviously  be  our  next  choice. 

It  is  evident,  however,  without  going  through  the  labor  of 
computation,  that  while  corn  meal  and  wheat  middlings  may 
be  used  in  the  ration,  neither  will  supply  enough  protein  if  used 
exclusively.  Of  the  available  feeding  stuffs  which  are  rich 
in  protein  and  which  may  therefore  serve  to  balance  the  de- 
ficiency of  this  ingredient,  gluten  meal  is  relatively  the  cheapest, 
and  cottonseed  meal  comes  next.  While  the  difference  be- 
tween the  two  is  not  great,  we  shall  naturally  try  the  cheaper 
one.  It  is  not  difficult  to  determine  by  a  few  trials  that  i\ 
pounds  of  corn  meal  and  3-3-  pounds  of  gluten  meal,  in  addi- 
tion to  the  coarse  fodder  available,  will  give  a  ration  corre- 
sponding very  closely  to  the  requirements,  as  the  following 
table  shows :  — 


2  z 


yo6 


NUTRITION  OF  FARM  ANIMALS 


TOTAL 

DIGESTIBLE 

NET 

DRY 

PROTEIN 

ENERGY 

MATTER 

VALUE 

Pounds 

Pounds 

Therms 

Corn  silage,  32  pounds  

8  4.2 

O  IQ 

c  OQ 

Clover  hay,  8  pounds     

6.97 

•39 

3-09 

Corn  meal,  2\  pounds 

2  22 

16 

213 

Gluten  feed,  3!  pounds  

3-18 

.98 

2-95 

Total     

20.79 

1.72 

13.26 

This  ration  shows  as  close  an  agreement  with  the  computed 
protein  requirement  as  could  be  desired,  but  contains  a  slight 
surplus  of  energy.  The  comparatively  low  figure  for  dry  mat- 
ter indicates  that  more  coarse  fodder  might  have  been  used  had 
it  been  available,  with  the  probable  effect  of  cheapening  the 
ration.  As  it  is,  we  have  used  the  feeds  relatively  lowest  in 
price  and  apparently  have  a  very  economical  ration. 

Cottonseed  meal,  however,  is  nearly  as  cheap  as  a  source  of 
energy  as  gluten  meal,  while  it  contains  considerably  more  pro- 
tein. It  seems  worth  while,  therefore,  to  see  whether  it  may 
not  be  possible  to  secure  the  necessary  protein  more  cheaply  by 
using  a  smaller  amount  of  the  former  feed  in  place  of  the  gluten 
meal.  Three  pounds  of  cottonseed  meal  will  supply  almost 
exactly  the  same  amount  of  protein  as  3^  pounds  of  gluten  meal. 
Making  this  substitution,  the  ration  stands  as  follows :  — 


TOTAL 
DRY 
MATTER 

DIGESTIBLE 
PROTEIN 

NET 
ENERGY 
VALUE 

Corn  silage  32  pounds 

Pounds 
84.2 

Pounds 
o  19 

Therms 

c  OQ 

Clover  hay,  8  pounds 

6  Q7 

-2Q 

•2  OQ 

Corn  meal,  i\  pounds     

2.22 

.16 

2.13 

Cottonseed  meal,  3  pounds 

2  77 

06 

2  7O 

Total     .... 

2O  38 

I  7O 

I  3  OI 

This  ration  agrees  with  the  computed  requirements  even  better 
than  the  previous  one,  while  a  simple  comparison  shows  that  it 
is  a  trifle  cheaper.  The  grain  portion  of  the  two  rations  costs 
as  follows:  — 


THE   COMPUTATION  OF  RATIONS 


707 


FIRST 
RATION 

SECOND 
RATION 

Corn  meal  

Cents 
3-13 

Cents 
3.11 

Gluten  meal 

473 

Cottonseed  meal       .          .... 

4  20 

Total 

7~86 

7  33 

It  thus  appears  that  the  ration  made  up  with  the  somewhat 
more  expensive  cottonseed  meal  is  actually  the  cheaper.  The 
difference,  to  be  sure,  is  small,  yet  for  30  cows  fed  for  200 
days  it  would  amount  to  $30.  Such  a  difference  is  only  likely 
to  be  found,  however,  when,  as  was  assumed  in  this  instance, 
some  feed  very  high  in  protein  can  be  had  at  a  relatively  cheap 
rate.  In  general,  it  may  be  said  that  when  there  are  no  very 
marked  differences  in  the  cost  of  a  Therm  of  energy  value  in 
the  feeding  stuffs  constituting  the  bulk  of  the  ration,  that  one 
of  the  various  high-protein  feeds  which  supplies  energy  at  the 
lowest  cost  should  ordinarily  be  used,  although  it  is  always 
wise  to  check  up  this  point,  as  in  the  example  just  given. 

804.  The  compounding  of  rations.  —  While  in  the  foregoing 
examples  an  exact  daily  ration  is  computed,  it  would,  of  course, 
be  utterly  impracticable  in  most  cases  to  weigh  out  separately 
each  day's  ration  for  each  animal.  Individual  weighings  of 
feeds  at  intervals  would  often  yield  valuable  information  and 
might  profitably  be  undertaken,  but  for  the  ordinary  routine 
of  feeding,  simpler  methods  must  be  used. 

When  practicable,  the  grain  feed  may  be  advantageously 
mixed  in  advance  in  the  desired  proportions  in  as  large  quan- 
tities as  the  storage  capacity  available  and  the  proper  preserva- 
tion of  the  materials  will  permit.  Where  facilities  are  available, 
the  whole  amount  of  grain  required  for  all  the  animals  may  be 
weighed  out  daily,  or  even  for  each  feeding,  without  much  ad- 
ditional labor.  In  distributing  the  grain  to  the  individual 
animals,  regard,  of  course,  should  be  paid  to  theif  productive 
capacity  and  their  individual  peculiarities.  The  ration  as 
computed  is  for  the  average  animal.  The  skill  of  the  feeder  is 
shown  in  adapting  it  in  quality  and  in  amount  to  the  individual. 


708  NUTRITION  OF  FARM  ANIMALS 

Doubtless  individual  weighings  at  intervals,  as  already  sug- 
gested, would  be  useful  as  a  control  on  the  accuracy  of  the 
distribution. 

The  weighing  of  coarse  fodder  is  usually  a  more  difficult 
problem  on  account  of-  its  bulk.  When,  however,  silage  or  cut 
fodder  is  handled  in  trucks,  the  matter  is  still  comparatively 
simple.  Long  fodder,  on  the  contrary,  is  not  readily  weighed. 
Nevertheless,  even  here  an  occasional  weighing,  if  practicable, 
as  a  control  upon  the  feeding,  is  very  desirable. 

In  all  these  and  similar  matters  common  sense  is  necessary. 
The  computed  ration  expresses  the  best  estimate  that  can  be 
made  of  the  actual  average  requirements,  but  it  is  at  best  more 
or  less  of  an  approximation.  It  would  be  foolish,  therefore,  to 
seek  extreme  exactness  in  realizing  it  or  to  go  to  more  expense 
in  the  weighing  and  apportioning  of  the  feed  than  the  saving  in 
the  latter  would  amount  to.  The  scale  upon  which  the  feeding 
is  conducted  will  play  an  important  part.  Where  scores  or 
hundreds  of  animals  are  being  fed,  an  exactness  may  profitably 
be  sought  which  would  be  absurd  in  the  case  of  two  or  three 
animals.  Finally,  it  should  be  remembered  that  these  com- 
puted rations  are  guides  and  not  recipes.  They  may  aid  the 
feeder  in  wisely  using  the  resources  at  his  command,  but  they 
cannot  take  the  place  of  experience  and  good  judgment. 


APPENDIX 


APPENDIX 


ESTIMATED   PROTEIN  AND  ENERGY   REQUIREMENTS   OF 
FARM  ANIMALS 

Compare  Chapter  XVIII,  §  2. 

TABLE  I.  —  MAINTENANCE  REQUIREMENTS  OF  CATTLE  AND  HORSES,  PER 
DAY  AND  HEAD 


CATTLE 

HORSES 

WEIGHT 

Digestible 
Protein 

Net  Energy 

Digestible 
Protein 

Net  Energy 

Metaboliz- 
able  Energy  l 

Pounds 

Pounds 

Therms 

Pounds 

Therms 

Therms 

ISO 

0.08 

1.69 

0.08 

1.16 

3.36 

250 

0.13 

2.38 

0.13 

1-63 

4-72 

500 

0.25 

3.78  / 

0.25 

2.58 

7-50 

750 

0.38 

4-95 

0.38 

3-39 

9.82 

IOOO 

0.50. 

6.00 

0.50 

4.10 

11.90 

1250 

0.63 

6.96 

0.63 

4.76 

13.80 

1500 

o-75 

7.86 

0-75 

5-37 

15-59 

TABLE  II.  —  MAINTENANCE  REQUIREMENTS  OF  SHEEP  AND  SWINE,  PER 
DAY  AND  HEAD 


LIVE 
WEIGHT 

SHEEP 

SWINE 

Digestible  Protein 

Net  Energy 

Digestible  Protein 

Net  Energy 

Pounds 

Pounds 

Therms 

Pounds 

Therms 

20 

o.on 

0.27 

O.OIO 

0-43 

40 

O.O22 

0.43 

0.019 

0.68 

60 

0.033 

0.56 

0.029 

0.89 

80 

0.044 

0.68 

0.038 

1.08 

IOO 

0.055 

0.79 

0.048 

1.25 

120 

O.o66 

0.89 

0.058 

1.41 

140 

0.077 

0.99 

0.067 

1.56 

160 

0.088 

1.09 

0.077 

1.71 

180 

0.099 

1.17 

0.086 

1.85 

200 

O.IIO 

1.25 

0.096 

1.99 

1  To  support  heat  production  of  animal  at  rest  (387). 
711 


712 


APPENDIX 


TABLE  III.  —  REQUIREMENTS   FOR  FATTENING  WITH  NO  CONSIDERABLE 

GROWTH  —  ALL  SPECIES  —  IN  ADDITION  TO  THE  MAINTENANCE 

REQUIREMENT 


PER  POUND  OF  INCREASE  IN 
LIVE  WEIGHT,  IN  ADDITION 

DIGESTIBLE  PROTEIN 

TO  THE  MAINTENANCE  RE- 
QUIREMENT 

PER  IOOO  LB.  LIVE 
WEIGHT,  IN  ADDI- 
TION TO  THE  MAIN- 

TENANCE REQUIRE- 

Digestible 
Protein  1 

Net  Energy 

Pounds 

Therms 

Pounds 

In  early  stages  .... 

0.15 

2.50 

In  late  stages     .... 
Average  for  entire  fatten- 

0.05 

4.00 

0.25-0.75 

ing  period       .... 

O.IO 

3-25 

TABLE  IV.  —  REQUIREMENTS  FOR  GROWTH  WITH  NO  CONSIDERABLE 
FATTENING 

a.  Per  Pound  of  Increase  in  Live  Weight,  in  Addition  to  the  Maintenance 

Requirement 


AGE 

CATTLE  (AND  SHEEP?) 

SWINE 

Minimum  of 

Minimum  of 

Digestible 
Protein  3 

Net  Energy 

Digestible 
Protein  3 

Net  Energy 

Months 

Pounds 

Therms 

Pounds 

.       Therms 

o-i 

0.23 

.170 

0.17 

0.65 

1-2 

O.22 

.272 

0.16 

0.77 

2-3 

0.22 

•374 

0.15 

0.88 

3-6 

O.2I 

.680 

0.14 

1.23 

6-9 

0.21 

.986 

0.12 

i-59 

9-12 

O.20 

2.292 

O.IO 

1.96 

12-18 

0.18 

2.904 

O.O7 

2.66 

18-24 

o.i  6 

3.000 

—  • 

— 

24-30 

0.14 

3-250 

1  Estimated  from  protein  content  of  increase. 

2  Estimated  from  experiments  on  fattening  (456). 

3  Estimated  protein  content  of  increase. 


APPENDIX 


b.  Per  Day  and  Head,  Including  Maintenance 
(i)  Cattle 


'      ] 

BEEF  BREEDS 

I 

)AIRY  BREED 

5 

AGE 

Live 
Weight 

Digestible 
Protein  1 

Net 
Energy 

Live 
Weight 

Digestible 
Protein  1 

Net 
Energy 

Months 

Pounds 

Pounds 

Therms 

Pounds 

Pounds 

Therms 

I 

125 

0.70 

3-7 

100 

0.40 

3-1 

2 

175 

0.85 

4.2 

135 

0-45 

3-4 

3 

200 

0.90 

4.2 

165 

0-55 

3-6 

6 

350 

•IS 

5-o 

275 

0.70 

4.1 

9 

450 

•25 

5-7 

325 

0-75 

4.4 

12 

550 

.40 

6-5 

400 

0.8o 

5-i 

iS 

750 

.40 

8.2 

550 

0.85 

6.4 

24 

goo 

•30 

9-3 

700 

0.85 

7-6 

30 

IOOO 

•30 

9-9 

800 

0.85 

8.2 

(2)  Sheep 


WOOL  BREEDS 

MUTTON  BREEDS 

AGE 

Live 
Weight 

Digestible 
Protein  1 

Net 
Energy 

Live 

Weight 

Digestible 
Protein  1 

Net 

Energy 

Months 

Pounds 

Pounds 

Therms 

Pounds 

Pounds 

Therms 

3 

37 

0.13 

0.78 

40 

0.22 

0.84 

6 

65 

O.l8 

0-95 

72 

0.30 

1.03 

9 

82 

0.17 

1.  06 

98 

0.28 

1.22 

12 

90 

0.15 

1.  12 

US 

0.25 

1.36 

18 

100 

0.12 

X.IQ 

ISO 

0.22 

1.64 

(3)  Swine 


AGE 

LIVE  WEIGHT 

DIGESTIBLE  PROTEIN  * 

NET  ENERGY 

Months 

Pounds 

Pounds 

Therms 

I 

15 

O.IO 

0.65 

2 

30 

O.2O 

I.OO 

3 

52 

0.30 

1.38 

6 

118 

0.40 

2.28 

9 

183 

0.50 

3.06 

12 

250 

o-SS 

3-80 

1  Based  on  Kellner's  standards. 


APPENDIX 


TABLE  V.  —  REQUIREMENTS  FOR  MILK  PRODUCTION 

Add  to  the  maintenance  requirement  the  following  amounts  for  each 
pound  of  milk  of  the  several  grades. 


GRADE  or  MILK 

DIGESTIBLE  PROTEIN 

NET  ENERGY 

Per  Cent  Fat 

Pounds 

Therms 

2-5 

0.041 

0.190 

3-o 

0.043 

0.214 

3-5 

0.045 

0.238 

4.0 

0.049 

0.265 

4-5 

0.052-^ 

0.291  - 

5-o 

0-055 

0.315 

5-5 

0.058 

0.338 

6.0 

0.06  1 

0.361 

6.5 

0.064 

0.385 

7.0 

0.068 

0.408 

TABLE  VI.  —  REQUIREMENTS  FOR  WORK  PRODUCTION  BY  THE  HORSE  (674) 
Per  1000  Pounds  Live  Weight 


DIGESTIBLE 
PROTEIN  x 

NET  ENERGY' 

Full  work  —  8  hrs  per  day 

Pounds 
2  O 

Therms 
18  2 

Half  work  —  4  hrs.  per  day       

1.4 

II  I 

One-fourth  work  —  2  hrs.  per  day      .... 

I.O 

7-6 

AVERAGE   DRY  MATTER,   DIGESTIBLE   PROTEIN  AND  NET 
ENERGY  VALUES    OF   FEEDING  STUFFS   PER   100  POUNDS 

Henry  and  Morrison  3  have  recently  published  a  very  valu- 
able compilation  of  American  analyses  of  feeding  stuffs  and  of 
the  results  of  American  digestion  experiments,  and  on  this  basis 
have  calculated  the  content  of  digestible  nutrients  in  a  great 
variety  of  feeding  stuffs. 

With  the  permission  of  these  authors  and  with  the  cooperation 
of  Assistant  Professor  Fred  Silver  Putney,  of  The  Pennsylvania 
State  College,  the  writer  has  computed  from  their  tables  the  net 

1  Kellner's  standards.  2  To  be  computed  from  Table  VIII. 

3  Feeds  and  Feeding,  isth  Edition,  pp.  633-666. 


APPENDIX 


715 


energy  values  of  the  more  important  feeding  stuffs  in  the  man- 
ner described  in  Chapter  XVII  (773,  774)  with  the  results  re- 
garding ruminants  reported  in  Bulletin  No.  142  of  the  Pennsyl- 
vania Experiment  Station  and  in  Bulletin  No.  459  of  the  U.  S. 
Department  of  Agriculture.  Those  results,  with  a  few  addi- 
tions and  corrections,  are  here  reproduced  and  the  computa- 
tion has  also  been  extended,  as  well  as  the  meager  basis  now 
available  will  permit,  to  the  data  regarding  swine  supplied  by 
Henry  and  Morrison's  tables.  The  figures  for  the  horse  are  de- 
rived in  part  from  the  same  source  and  in  part  from  Zuntz 
and  Hagemann's  investigations,  the  net  energy  values  being 
computed  according  to  the  method  proposed  by  those  investi- 
gators (775-778).  The  tables  show  primarily  the  net  energy 
values  for  maintenance  or  fattening.  There  seems  good  reason 
for  believing,  however,  that  they  may  be  taken  without  serious 
error  to  represent  also  the  net  energy  values  for  growth  and 
for  work  production  and  at  least  the  relative  values  for  milk 
production. 

Henry  and  Morrison's  tables  include  only  the  crude  protein 
(N  X  6.25).  The  amount  of  non-protein  has  been  estimated 
from  the  crude  protein  by  the  writers  on  the  basis  of  Kellner's 
averages. 

TABLE  VII.  —  VALUES  PER  TOO  POUNDS  FOR  RUMINANTS 


Duv 

DICES 

TIBLE 

NET 

MATTER 

Crude 
Protein 

True 
Protein 

ENERGY 

VALUE 

DRIED  ROUGHAGE 
Hay  and  fodder  from  cereals 
Bronie  grass  smooth 

Pounds 
01   ? 

Pounds 
c  o 

Pounds 

3r 

Therms 
4.O  8^ 

Corn  (maize)  fodder  (ears  included,  medium 
dry) 

81.7 

3-O 

2.3 

42.04 

Corn  (maize)  stover  (ears  removed,  medium 
dry) 

81.0 

2.1 

1.6 

31.62 

Kafir  fodder  high  in  water 

71  7 

•7   Q 

i  8 

74  28 

Kafir  stover  high  in  water           ..... 

72.7 

1.4 

I.O 

27.6? 

Millet,  Hungarian      

85.7 

<?.o 

2.O 

46.06 

]Mixed  timothy  and  clover                           . 

87  8 

e  •} 

3  6 

40.8? 

Oat  hay  

88.0 

4.C 

5.Q 

32.  2< 

716 


APPENDIX 


TABLE  VII.  —  VALUES  PER  100  POUNDS  FOR  RUMINANTS*(COW&'WW< 


DICES 

5TIBLE 

NET 

MATTER 

Crude 
Protein 

True 
Protein 

ENERGY 
VALUE 

DRIED  ROUGHAGE 
Hay  and.  fodder  from  cereals 
Orchard  grass   .          

Pounds 
88  4 

Pounds 

Pounds 

Therms 
AA  O"? 

Prairie  hay  

Q-2     C 

A.  O 

•6 

2  Q 

4.O  A2 

Red  top 

A  6 

CI  22 

Sorghum  fodder,  computed  to  80  per  cent  dry 
matter       
Timothy  all  analyses 

yu.z 

8o.O 

88  4 

2-5 

•y 

i-5 

5  •«•••«<« 

32.20 

Timothy,  before  bloom  . 

Q2  8 

O'u 

A3  ?2 

Timothy,  early  to  full  bloom  
Timothy,  late  bloom  to  early  seed    .... 
Timothy,  nearly  ripe      

Hay  and  fodder  from  legumes 
Alfalfa,  all  analyses 

87.2 
85.1 
87.5 

3.6 

2.4 

2.2 

2-5 
1.8 

1.8 

47.40 

37-54 
38.59 

Alfalfa,  before  bloom 

91.4 

Oo    g 

o4-^o 

-26  21 

Alfalfa,  in  bloom   

VO'0 

O2  < 

A3-4 

IO  ^ 

i<J'6 

6  7 

OU'^O 
7.2    '?'? 

Alfalfa,  in  seed 

89  6 

8  cr 

6  2 

Clover,  alsike    . 

87  7 

°o 

O-^'^O 

Clover,  crimson     

80  A. 

97 

•o 
6  o 

^6  21 

Clover,  red  all  analyses 

87   T 

7  6 

oS  6g 

Clover,  red,  before  bloom    . 

89  6 

ii  6 

•y 

A2  17 

Clover,  red,  in  bloom      

86  i 

8  i 

•4 

e  -? 

•2Q   I  2 

Clover,  red,  after  bloom 

6  8 

Clover,  sweet  white   . 

/  /•y 

O 

6  7 

O4O1 
3.8  08 

Cowpeas,  all  analyses     

OO  1 

T  -2     T 

92 

77    CQ 

Cowpeas,  before  bloom 

T7  8 

12  8 

Cowpeas,  in  bloom  to  early  pod  . 

80  A 

12  6 

OOO4 

7Q     T  T 

Soybeans      

OI  A. 

117 

8  8 

AA  O7. 

Straws 
Barley      

8?  8 

o  6 

76  6l 

Buckwheat  

QO  I 

42 

7    2 

4e  r 

Oat      

88  <: 

o  8 

tA  8l 

Rice    

°°>o 
02  ^ 

O  O 

27    6? 

Rye     

Q2  Q 

O  7 

O  'J 

17  ^Q 

Wheat      

91  6 

7  22 

U«O 

APPENDIX    v  717 

TABLE  VII.  —  VALUES  PER  100  POUNDS  FOR  RUMINANTS  (Continued) 


DRY 

MATTER 

DIGESTIBLE 

NET 
ENERGY 
VALUE 

Crude 
Protein 

True 
Protein 

FRESH  GREEN  ROUGHAGE 
Green  cereals,  etc. 
Barley  fodder    

Pounds 

23.2 
23-8 
36.4 
43-6 
36.6 
8.9 
14.1 
23.1 
14.9 
19.9 
25.1 
26.2 
34-8 
20.7 
10.6 
15.0 

21.  0 
27.9 
10.0 

20.3 
21.5 
27.6 

26.1 

29.2 
16.7 
21.3 
24.9 
24.2 
32.1 
46.4 
27.4 

19.9 

25-9 
29.8 

24.3 
17.4 

Pounds 

2-3 
3-7 
2.8 
1.9 
2.2 
1.9 

i-7 

I.O 

i.i 

I.O 

1-3 

i.i 

i-5 

I.O 

0.9 
0.9 

I.O 
1.2 

0.8 

1.2 
I.O 
1.9 
2-3 

i-7 

2.6 
2.1 
0.7 

1.8 
i-3 
i-5 

2.8 

3-5 
3-3 

2.1 
2-7 
2-3 

Pounds 

2.O 
2.8 
2.2 
1.6 
1-5 

i-3 

i.i 

0.8 
0.8 
0.8 

I.O 

0.8 
i.i 
0.8 
0.7 
0.7 
0.8 
0.9 
0.6 

0.9 
0.8 
i.i 

2.0 
X.I 

1-7 
1.4 

0.4 
I.I 

0.8 

I.O 

1.9 

1.9 
1.8 
i-3 

i-S 

1.6 

Therms 

14.08 
14.82 
17.77 
2I.OI 

17.78 
8.87 
7-05 
14.60 
9-52 
13.64 

17-35 
16.74 
22.48 

13-53 
6.89 
10.39 

13-49 
17.84 
7.82 

13.38 
14.26 
17.24 
14.06 
IS.Sl 
13.07 
15-99 
15-37 
18.36 
18.89 
26.36 
18.75 

9-2O 
11.50 
II.  IO 
14.56 
10.83 

Blue  grass,  Kentucky,  before  heading  .     .     . 
Blue  grass,  Kentucky,  headed  out    .... 
Blue  grass,  Kentucky,  after  bloom  .... 
Buckwheat  Japanese               .               ... 

Cabbage  

Cabbage  waste  outer  leaves 

Corn  (maize)  fodder,  dent,  all  analyses     .     . 
Corn  (maize)  fodder,  dent,  in  tassel      .     .     . 
Corn  (maize)  fodder,  dent,  in  milk  .... 
Corn  (maize)  fodder,  dent,  dough  to  glazing  . 
Corn  (maize)  fodder,  dent,  kernels  glazed 
Corn  (maize)  fodder,  dent,  kernels  ripe     .     . 
Corn  (maize)  fodder,  flint,  all  analyses      .     . 
Corn  (maize)  fodder,  flint,  in  tassel       .     .     . 
Corn  (maize)  fodder,  flint,  in  milk   .... 
Corn  (maize)  fodder,  flint,  kernels  glazed 
Corn  (maize)  fodder,  flint,  kernels  ripe      .     . 
Corn  (maize)  fodder,  sweet,  before  milk  stage 
Corn  (maize)  fodder,  sweet,  roasting  ears  or 
later     ...          

Corn  (maize)  fodder,  sweet,  ears  removed 
IVlillet  Hungarian 

Oat  fodder    

Orchard  grass 

Rape   .     .          .          ...          .     .          .     . 

Rye  fodder  

Sweet  sorghum  fodder 

Timothy,  before  bloom  
Timothy,  in  bloom 

Timothy,  in  seed        

Wheat  fodder 

Green  legumes 
Alfalfa  before  bloom      

Alfalfa  in  bloom 

Alfalfa  after  bloom    

Clover  alsike 

Clover  crimson          .... 

7l8  APPENDIX 

TABLE  VII.  —  VALUES  PER  100  POUNDS  FOR  RUMINANTS  (Continued) 


Thjv 

DICES 

>TIBLE 

NET 

MATTER 

Crude 
Protein 

True 
Protein 

ENERGV 
VALUE 

FRESH  GREEN  ROUGHAGE 
Green  legumes 
Clover,  red,  all  analyses      
Clover  red  in  bloom      ... 

Pounds 

26.2 
27  ? 

Pounds 

2-7 

2.7 

Pounds 
1-7 

1.8 

Therms 

15.87 
16.74 

Clover,  red,  rowen     
Cowpeas  . 

34-4 
16.3 

3-3 
2.3 

2.2 
1.7 

17.30 
10.42 

Peas,  Canada  field     
Soybeans,  all  analyses    
Soybeans,  in  bloom    
Soybeans,  in  seed  . 

16.6 
23-6 

20.8 
24.  2 

2-9 

3-2 
3-o 
3.1 

2.1 
2.4 

2-3 
2.5 

9.78 

12-53 
10.44 
12.70 

Vetch,  hairy      

SILAGE 
Corn  (maize),  well-matured,  recent  analyses  . 
Corn  (maize)   immature      ...               . 

18.1 

26.3 

21  O 

3-5 
i.i 

I.O 

2.4 

0.6 
0.4 

11-95 

15.90 
11.96 

Corn  (maize),  from  frosted  ears  
Corn  (maize),  from  field-cured  stover   .     .     . 
Clover      

25-3 
19.6 
27.8 

1.2 

0-5 
I.  a 

0.6 

0-3 

0.8 

14.27 
8.98 
7.26 

Cowpeas 

22  O 

i  8 

i.i 

H.O5 

Soybeans                               . 

27  I 

2.6 

1.5 

11.59 

Sugar  beet  pulp     

IO.O 

0.8 

0.5 

9.32 

ROOTS,  TUBERS,  AND  FRUITS 
Apples 

18  2 

O.4 

O.I 

15.92 

Beets,  common           

I^.O 

O.O 

O.I 

7.84 

Beets,  sugar      

16.4 

1.2 

0.4 

11.20 

Carrots                                                • 

II.  7 

O.O 

0.5 

9.21 

Mangels  

0.4 

0.8 

O.I 

5.68 

21.2 

i.i 

O.I 

18.27 

Potato  flakes                        

87.0 

3.6 

0.4 

72.68 

Potato  flour      

8o.4 

1.4 

O.I 

80.09 

Pumpkins  field 

8.3 

i.i 

0.6 

6.O5 

Rutabagas                  

IO.O 

I.O 

0.3 

8.46 

Turnips   

Q.C 

I.O 

0.4 

6.16 

GRAINS 
Cereal  grains 
Barley                              ........ 

00.7 

9.0 

8-3 

89.94 

B  uck  wheat 

87.0 

8.1 

7.2 

59-73 

Corn  (maize)   dent                        

80.5 

7-5 

7.0 

85.50 

Corn  (maize),  flint     
Corn  (maize)  and  cob  meal               .... 

87.8 
89.6 

7-7 
6.1 

7-2 

5-7 

84.00 
75.80 

APPENDIX  719 

TABLE  VII.  —  VALUES  PER  100  POUNDS  FOR  RUMINANTS  (Continued) 


DRY 

MATTER 

DIGESTIBLE 

NET 
ENERGY 
VALUE 

Crude 
Protein 

True 
Protein 

GRAINS 

Cereal  grains 
Corn  (maize)  meal     
Oats    

Pounds 

88.7 
90.8 
92.1 
90.4 
90.6 

87-3 
89.8 

89.1 
89.9 

86.6 
88.4 
90.8 
89.1 
93-5 
94.0 
90.1 

90.6 
90.8 
95-5 
93-i 

9.4 
13-6 
9.9 
9.6 
91.7 
6.6 

92.5 

91.8 
24.1 

93-4 
92.8 

Pounds 

6.9 
9-7 

12.8 

4-7 
9-9 
7-5 
9.2 

8-7 
9.2 

18.8 
19.4 
19.0 
19.8 
19.4 
24.1 
30.7 

13-3 

2O.6 

23-3 
13-5 

3-4 
3-3 
3-6 
3-i 
34-4 
0.8 

21.5 

18.7 
4.6 
22.4 
13-6 

Pounds 

6.4 
8-7 
n-5 
4-5 
9.0 

6-7 
8.1 

7-7 
8.1 

16.4 
16.9 
16.6 
17.2 
16.9 

22.2 
27-3 

II.9 
I9.2 
20.  2 

11.7 

3-4 
3-3 
3-6 
3-1 
34-4 
0.8 

20.  2 
17-5 

4-4 
18.3 
ii.  i 

Therms 

85.20 
67.56 
86.20 

77-33 
93-71 
89-7S 
91.82 
91.66 
91.41 

73-29 
79-46 
78.72 
77.62 

83-15 
109.04 
81.29 

78.33 
83-17 
95-77 
92.49 

I3-32 
29.01 
i4-3i 
15-43 
103.91 
10.39 

53.38 

50.93 
14-53 
85.08 
56.01 

Oatmeal                 

Rice  rough       

Rve 

Sorghum  grain            

W^heat  all  analyses 

\Vheat  winter 

Wheat,  spring  

Leguminous  seeds 
Beans,  navy      

Cowpeas 

Peas  field     .                         

Pea  meal      

Peanuts  with  hull 

Peanut  kernel        

Oil  seeds 
Cottonseed. 

Flaxseed       

Sunflower  seed                                              . 

Sunflower  seed  with  hulls    

DAIRY  PRODUCTS 
Buttermilk                                .               ... 

Cow's  milk  

Skim  milk  —  centrifugal     .     .               . 

Skim  milk  —  gravity      
Skim  milk  —  dried                        • 

Whey       

BY-PRODUCTS 
Fermentation  industries 
Brewers'  grains,  dried     
Brewers'   grains,   dried,   below   25   per  cent 
protein                

Brewers'  grains  wet 

Distillers'  grains,  dried,  from  corn    .... 
Distillers'  grains,  dried,  from  rye      .... 

720  APPENDIX 

TABLE  VII.  — VALUES  PER  100  POUNDS  FOR  RUMINANTS  (Continued] 


DRY 

MATTER 

DIGESTIBLE 

NET 
ENERGY 
VALUE 

Crude 
Protein 

True 
Protein 

BY-PRODUCTS 

Fermentation  industries 
Distillers'  grains,  wet      

Pounds 

22.6 

94-2 
92.4 

88.8 
89.7 
88.0 
89.9 
88.9 
89.9 

QO-5 
90.0 
88.6 
89.9 

89.3 
89.6 

90.4 
92.3 
90-3 
92.5 
92.2 
91.1 
90.4 
90.9 
89.6 

89.3 
94.4 
88.2 
90.0 

9i-3 
90.9 
90.7 
33-4 

74-7 
74.2 

Pounds 

3-3 
15-8 
20.3 

10.5 
0.4 
24.6 
7.0 
14.8 
7-9 
7-3 
8.0 

12.2 
12-5 
15-7 
13-4 

18.8 
18.4 
o-3 
37-0 
33-4 
16.5 
31-7 
30.2 
12.4 
42.8 

20.  2 
38.1 
32.0 

21.6 

30.2 

II.  2 
4.1 

I.I 

I.O 

Pounds 

2.8 
n.8 
12.5 

9.1 

? 
20.8 

6.5 

13.2 
7.0 

6.4 
*  7-i 
10.5 
10.8 
14.0 

I2.O 
I8.3 

18.0 

? 

35-4 
32.0 

14-3 
30-9 
28.5 

12.0 
41.4 
I9.S 
37-3 
29.1 

20.1 
28.1 
9.2 

3-7 

o.o 
o.o 

Therms 

22.05 
87.82 
72.72 

30-59 
-7.69 
72.19 
88.78 
78.80 

45-29 
65.24 

77-7° 
79-35 
53-00 

75-02 
59.10 

83-49 
100.31 
9.92 
93-46 
90.00 
83.88 
85.12 
88.91 
94.18 
93-55 
42.57 
99.65 
88.87 

80.72 

84-iS 
77.46 
30.45 

57-10 
55-38 

Malt    

Malt  sprouts     

Milling 
Buckwheat  bran    . 

Buckwheat  hulls    

Buckwheat  middlings     

Hominy  feed 

Red  dog  flour    

Rice  bran,  high  grade     
Rice  meal     ... 

Rice  polish   

Rye  bran 

Wheat  bran       ...               ... 

Wheat  middlings,  flour  

\Vheat  middlings  standard 

Oil  extraction 
Cocoanut  meal,  low  in  fat 

Cocoanut  meal,  high  in  fat      
Cottonseed  hulls 

Cottonseed  meal,  choice 

Cottonseed  meal,  prime      
Germ  oil  meal  maize 

Linseed  meal,  new  process  .               ... 

Linseed  meal,  old  process    
Palmnut  cake 

Peanut  cake  from  hulled  nuts      .... 

Peanut  cake,  hulls  included     
Soybean  meal,  fat  extracted    
Sunflower  seed  cake  

Starch  manufacture 
Gluten  feed       ...                   

Gluten  meal      

Starch  feed  dry 

Starch  feed,  wet    .          .     .          

Sugar  manufacture 
Molasses  beet 

Molasses,  cane  or  black  strap      

APPENDIX  721 

TABLE  VII.  — VALUES  PER  100  POUNDS  FOR  RUMINANTS  (Continued) 


DRY 

DICES 

TIBLE 

NET 

MATTER 

Crude 
Protein 

True 
Protein 

ENERGY 
VALUE 

BY-PRODUCTS 

Sugar  manufacture 
Molasses  beet  pulp    

Pounds 
Q2.A 

Pounds 
r.O 

Pounds 
•i  e 

Therms 
76  28 

Sugar  beet  pulp  dried 

91  8 

A6 

O  7 

75  8? 

Sugar  beet  pulp,  ensiled      

IO  O 

08 

O  5 

O  12 

Sugar  beet  pulp,  wet      

O.7 

O  "? 

o.c 

8  oo 

Packing  house 
Dried  blood       

QO.l 

60  I 

686 

68  12 

Tankage 
Over  60  per  cent  protein      

02  6 

*8  7 

<;<;  6 

Ql  O4. 

55—60  per  cent  protein     

Q2.C 

1:4.  o 

CI.I 

ST.  58 

4S~5S  per  cent  protein 

Q2  5 

A8  I 

AS  e 

72  06 

Below  45  per  cent  protein    .     .     .     .  •  . 

Q-2    C 

17  6 

is  6 

CA  16 

TABLE  VIII.  —  VALUES  PER  100  POUNDS  FOR  THE  HORSE 


• 

DICE 

5TIBLE 

NET 

MATTER 

Crude 
Protein 

True 
Protein 

ENERGY 
VALUES 

Alfalfa  hay 

Pounds 
OI  4. 

Pounds 
IO  Q 

Pounds 

7  d 

Therms 
48  82 

Red  clover  hay    ....          . 

87  I 

7  2 

4  5 

•7Q  Q4. 

Timothy  hay  

88.4 

i.3(?) 

o.5(?) 

26.64 

Wheat  straw 

oi  6 

08 

O  4. 

—  2O  QO 

Beans     

10  "? 

17.  1 

IOQ  4.O 

Corn  (maize)    dent 

80  «; 

r  Q 

5     A 

112  80 

Corn  (maize),  meal  

88  7 

7  I 

66 

112  7O 

Oats  

00.8 

0  Q 

8.Q 

01.44 

Peas  .     . 

QO  8 

18  7 

16  i 

IO5  2O 

Linseed  cake  

QO.Q 

20  5 

27.8 

101.60 

Carrots 

117 

I  2 

08 

16  60 

Potatoes 

21  2 

I  O 

O  Q 

I1?  7O 

722  APPENDIX 

TABLE  IX.  —  VALUES  PER  100  POUNDS  FOR  SJSONE 


DRY 
MATTER 

DIGESTIBLE 

NET 
ENERGY 
VALUES 

Crude 
Protein 

True 
Protein 

Grains 
Barley    .     . 

Pounds 
90.7 

89.5 
88.7 
89.6 
89.1 
90.4 
90.6 

87.3 
89.8 

88.9 
89.9 
89.5 

90.9 

88.2 

90-3 
92.6 

21.2 
9.9 

Pounds 
8.8 
7.6 
7-i 
6-5 
21.4 

6-5 
9.9 

5-5 
9.9 

14.8 

12.0 
14.4 

28.8 

34-8 

59-2 
44-8 
1.8 
3-8 

Pounds 
8.1 

7-1 
6.6 
6.1 

18.8 

6.3 

9.0 

4-7 

8.8 

13.2 
10.3 
12.7 

27.1 
34-o 

58.7 
41.7 
0.8 
3-8 

Therms 
106.08 
118.82 
120.25 
103.30 
122.43 
110.98 
123.68 
100.59 
108.85 

107.02 
74-95 
103.73 

110.85 
108.42 

116.89 
109.39 
24.69 
14.74 

Corn  (maize),  dent  
Corn  (maize)  meal 

Corn  (maize)  and  cob  meal    .... 
Pea  meal 

Rice,  rough     

Rve   . 

Sorghum  seed       

Wheat    

Milling  products 
Red  dog  flour       

Wheat  bran     

Wheat  middlings,  standard    .... 

Oil  meals 
Linseed  meal,  old  process      .... 
Soybean  meal       .... 

Sundries 
Dried  blood     

Tankage,  over  60  per  cent  'protein  .     . 
Potatoes     .         ... 

Skim  milk  

APPENDIX 


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INDEX 


Abomasum,  80 

Accessory  substances,  348,  421 

significance  of,  632 
Acid: 

hippuric,  163 

hippuric,  synthesis  of,  163 
uric,  synthesis  of,  171 
Acidity  in  ash,  significance  of,  341 
Acidosis,  336 
Acids : 

excretion  of,  338 
influence  on  digestibility,  627 
neutralization  of,  337 
nucleic,  34 
anabolism,  168 
autogenesis,  169 
cleavages,  170 
deaminization,  171 
katabolism,  170 
metabolism,  168 
synthesis,  169 
organic,  40 

formation  of,  in  digestion,  40,  158 
in  feeding  stuffs,  40 
metabolism  of,  159 
Adipose  tissue,  58,  424 

composition  of,  59 
Age: 

best  for  fattening,  436 
influence  on 

composition  of  gain,  431 
cost  of  production  of  meat,  430 
digestibility,  610 
effects  of  temperature,  454 
energy    requirements    for    mainte- 
nance, 307 

feed  consumption,  431 
net  energy  values,  666 
production  of  lean  meat,  433 
relation  of  growth  to,  373 
relation  of  protein   requirements  to, 

445 

Albuminoids,  33 
Albumins,  33 


Alfalfa  proteins,  value  of,  683 
Alkali  ratio  of  ash,  342 
Alkaloids,  37 
Amids,  37 

occurrence  in  plants,  38 
Amino  acids,  37 

from  simple  proteins,  28,  29 

occurrence  in  plants,  38 

relative  values  for  growth,  381 

required  for  maintenance,  314 
Ammonia,  formation  of,  in  katabolism  of 

proteins,  165 
Amount  of  feed,  influence  on 

effects  of  temperature,  454 

meat  production,  443,  449 

metabolizable  energy,  664 

milk  production,  515 

net  energy  values,  664 

production,  269 

of  methane,  665 
Amylase,  78,  86 
Amylopsin,  78,  86 
Anabolism,  145 

of  fats,  171 

nucleic  acids,  168 
phosphorus,  180 
simple  proteins,  160 
Animal : 

as  factor  in  meat  production,  428 
milk  production,  470 

as  prime  motor,  192 
Araban,  15 
Arabinose,  9 
Arteries,  126 
Ascent,  work  of,  551 

efficiency  of  body  in,  551 
Ash,  5 

acid  and  basic,  340 

alkali  ratio  of,  342 

balance,  216 
maintenance  of,  339,  344 

body,  proportion  of  in  bone,  48 
in  offal,  56 

bone,  composition  of,  48 


725 


726 


INDEX 


Ash,  —  continued 
content  of  feed,  332 
correction  of  deficiencies  in,  346 
determination  of,  in  feeding  stuffs,  67 
digestion  of,  101 
effects  of  deficiency  of,  420 
ingredients,  6 

availability  of,  417 

balancing  of,  in  ration,  343 

deficiencies  in,  339 

digestibility  of,  118,  333,  343 

excretion  of,  141 

functions  of,  187 

indispensable,  332 

metabolism  of,  178 

skeleton  as  reserve  of,  338 
losses  of,  334 

causes  of,  334 
of  milk,  460 

sources  of,  468 
outgo  of,  in  milk,  520 
proportion  of,  in  animal,  5 

in  feeding  stuffs,  5 
rate  of  storage  of,  in  growth,  414 
requirements  for  growth,  414 

maintenance,  332 

milk  production,  520 

work  production,  562 
significance  of  acidity  in,  341 
supply  in  dairy  rations,  521 
total    retention    of,    during    growth, 

416 

Assimilative  power : 
influence  of  breed  on,  441 

individuality  on,  441 
Autogenesis  of  nucleic  acids,  169 

Balance : 
of  ash,  216 
carbon,  205 

example  of,  206 
energy,  216 

example  of,  240 
income  and  expenditure,  194 
matter,  202 
nitrogen,  202 

determination  of,  203 
example  of,  203 
nutrition,  192,  201 

includes  energy,  216 
water,  216 

Balance  experiments,  200 
comparison  with  metabolism  investi- 
gations, 241 
practical  experiments,  244 


Balance  experiments,  —  continued 

in  agricultural  investigations,  243 

significance  of  results  of,  241 
Barley  feed,  585 
Bases,  organic,  37 
Bile,  86 
Blood,  123 

coagulation  of,  125 

corpuscles,  red,  124 
white,  124 

course  of,  127 

plasma,  125 

platelets,  124 
Body: 

comparison  with  power  plant,  567 

composition  of  entire,  61 
fat-  and  ash-free,  65 
fat-free,  64 

efficiency  of.     (See  Efficiency) 

expenditure  by,  192 

schematic,  195 

substances  sources  of  energy  for  work, 
544 

temperature,   chemical  regulation  of, 

263 

physical  regulation  of,  262 
Bone,  47 

ash  composition  of,  48 

composition  of,  47 

proportion  of  body  ash  in,  48 

protein  in,  48 

Bones  as  reserve  of  ash  ingredients,  338 
Bran,  582 

rice,  583 

rye,  582 

wheat,  582 

Breakfast  food  residues,  584 
Breathing : 

mechanics  of,  134 

regulation  of  rhythm  of,  137 
Breed,  influence  on 

assimilative  power,  441 

composition  of  milk,  473 

composition  of  milk  solids,  474 

digestive  power,  440,  610 

early  maturity,  441 

feed  consumption,  443 

maintenance  requirements,  442 

meat  production,  440 

net  energy  values,  666 
Brewers'  grains,  586 
By-products,  582 

nature  of,  582 

of  fermentation  industries,  585 
milling,  582 


INDEX 


727 


By-products,  —  continued 

uses  of,  584 
oil  extraction,  586 

starch  and  glucose  manufacture,  587 
sugar  manufacture,  588 
the  packing  house,  590 

Calcium : 

metabolism  of,  181 
occurrence  of,  6 
Calorimeters,  221 
animal,  235 
emission,  236 
latent  heat,  236 
respiration,  236 
water,  236 
Calves : 

energy  requirements,  399 
•  gains  by,  in  growth,  400 

protein  requirements,  404 
Capillaries,  126 
Carbohydrates,  7 

cause  of  diminished  digestibility  of,  621 
classification  of,  8 
digestible,  121 
digestion  of,  89 

formation  of  fat  from,  155,  174 
from  fats,  178 
proteins,  167 
formed  in  the  body,  155 
functions  of,  186 
influence  of  excess  of,  on  digestibility, 

616 

feeds  rich  in,  on  digestibility,  617 
katabolism  of,  156 

intermediary,  157 
metabolism  of,  152 
occurrence  of,  7 
of  milk,  460 

origin  of,  467 
pentose,  9,  15 

metabolism  of,  157 
relative  utilization  of   fats  and,   for 

work  production,  553 
Carbon  balance,  205 

example  of,  206 
Carbon  dioxid : 
excretion  of,  139 

determination  of,  208 

through  the  skin,  139 

formed  in  respiration,  136 

product  of  metabolism,  144 

Carnivora,  influence  of  feed  consumption 

on  heat  production  by,  657 
Cartilage,  49 


Cattle: 

energy  requirements  for  growth,  339 
maintenance,  288 

influence  of  feed  consumption  on  heat 
production,  651 

maintenance    requirements    of,    com- 
pared with  sheep,  294 

net  energy  values  for,  659 
computation  of,  667,  673 

protein  requirements  for  growth,  404 

maintenance,  326 
Cell,  42 

enclosures,  45 

nucleus,  42 

structure,  42 

wall,  44 
Cellulose,  12 

digestion  of,  89 

fermentation  of,  90 
Cereal  grains,  579 

composition  and  digestibility  of,  580 

uses  of,  581 

values  of  proteins  of,  682 
Cerebrosids,  23 

Changes  in  digestion,  summary  of,  101 
Chemical  changes  in  muscular  contrac- 
tion, 532 

Chlorin,  occurrence  of,  7 
Choice  of  feeding  stuffs,  703 
Cholesterins,  22 
Chymosin,  83 
Circulation,  123 

adjustment  of,  131 

influence  of  work  on,  535 

mechanics  of,  128 

scheme  of,  127 
Cleavage   products,   proportions  of,   in 

simple  proteins,  31 
Coagulation  of  blood,  125 
Coarse  fodders,  72,  572 

general  character  of,  572 

proportion  of  vegetative  organs  in,  576 
Coecum,  84 
Collagens,  33 
Colloids,  conversion  of,  into  crystalloids 

in  digestion,  102 
Colon,  85 
Combustible  gases,   outgo  of   chemical 

energy  in,  230,  636 
Combustion,  heat  of,  223,  227 
Compounding  of  rations,  707 
Computation : 

of  improvement  of  a  ration,  698 
rations,  689 
from  given  feeding  stuffs,  700 


728 


INDEX 


Computation,  —  continued 

method  of,  697 
of  total  feed  required,  697 
Concentrates,  72,  579 
comparison  with  roots,  579 

roughage,  662 

determination  of  digestibility  of,  115 
proportion  of,  to  roughage,  451,  696 
relative  values  for,  671 
Condiments,    influence    of,    on    digesti- 
bility, 627 

Condition,  influence  of, 
on  economy  of  gain,  438 
meat  production,  438 
rate  of  gain  in  fattening,  438 
Conditions   affecting   digestibility,    60 1, 

602,  613 

Conditions,    external,    influence   of,    on 
meat  production,  453 
milk  production,  478 
Conformation,  relation  of,  to  meat  pro- 
duction, 443 

Conservation  of  energy,  219 
Contraction,  muscular,  532 
chemical  changes  in,  532 
energy  transformations  in,  533 
Corn  bran,  588 
Cottonseed  meal,  587 
Critical  temperature,  264,  453 

lowered  by  feed  consumption,  308 
Crude  fiber,  13 

composition  of  digested,  120 
correction  of   net  energy  values  for, 

669 

determination  of,  in  feeding  stuffs,  71 
influence  of,   on  heat  production   of 

horse,  676 

proportion  of  pentosans  in,  71 
Cutaneous  excretion,  outgo  of  chemical 

energy  in,  231 
Cutting  of  roughage,   influence  of,   on 

digestibility,  624 
Cytoplasm,  42 

Dairy  rations : 

addition  of  fat  to,  517 

ash  in,  521 

protein  in,  506 
Deaminization : 

of  nucleic  acids,  171 
simple  proteins,  165 

reversible,  166 
Deficiencies  in  ash : 

correction  of,  346 

effects  of,  420 


Dextrins,  14 
Dextrose,  8 

Digestible  nutrients.     (See  Nutrients) 
Digestibility,  in,  601 
apparent,  120 

by  horse  compared  with  ruminants, 
604 

species  of  ruminants,  603 

swine  compared  with  ruminants,  606 
conditions  affecting,  60 1 
definition  of,  in 
determination  of,  in,  114 

influence  of  excretory  products,  118 
influence  on, 

of  acids,  627 

addition  of  protein,  622 

age,  6 10 

breed,  610 

condiments,  627 

conditions  relating  to  the  animal,  602 
feed,  613 

cutting  of  roughage,  624 

drinking,  628 

drying,  623 

excess  of  carbohydrates,  616 

feeds  rich  in  carbohydrates,  617 

grinding  of  grain,  624 

heavy  feeding,  450 

individuality,  609 

non-protein,  622 

protein  supply,  447 

quantity  of  feed,  613 

roots,  618 

species,  603 

tubers,  618 

water  drinking,  628 

work,  6 10 

laboratory  determination  of,  116 
of  ash  ingredients,  118,  333,  343 

carbohydrates,  diminished,  cause  of, 
621 

cereal  grains,  580 

concentrates,  determination  of,  115 

ether  extract,  119 

grasses,   influence  of  maturity  on, 

574 
maize  forage,  influence  of  maturity 

on,  575 

nitrogenous  substances,  119 
protein,  diminished,  cause  of,  619 
variable,  60 1 

variation  of,  at  different  times,  602 
Digestion,  77 
changes  in,  101 
chemistry  of,  89 


INDEX 


729 


Digestion,  —  continued 

conversion   of    colloids   into    crystal- 
loids in,  102 

experiments,  example  of,  114 
methods  of,  112 
time  required  for,  113 
extent  of  protein  cleavage  in,  98 
intestinal,  87 

molecular  simplification  in,  103 
of  ash,  101 
carbohydrates,  89 
cellulose,  89 
disaccharids,  95 
electrolytes,  101 
fats,  88,  95 
hemicelluloses,  92 
non-proteins,  96,  100 
nucleic  acids,  99 
pentosans,  91 
phosphorus,  101 
proteins,  83,  88,  95 
by  erepsin,  98 
pepsin,  96 
trypsin,  97 
starch,  79,  88,  92 
in  intestines,  94 

stomach,  93 
sulphur,  101 
organs  of,  77 

general  plan  of,  77 
solution  of  nutrients  in,  101 
uniformity  of  nutritive  material,  103 
work  of,  277 

differences  between  feeding  stuffs,  663 
roughage    compared    with    concen- 
trates, 662 
Digestive  power,  influence  of  breed,  440 

individuality,  440 
Diminishing  returns  from  feed  in  milk 

production,  515 
Disaccharids,  10 
digestion  of,  95 
general  properties  of,  n 
Distillers'  grains,  586 
Draft,  work  of,  552 

efficiency  of  body  in,  552 
Dried  blood,  500 
Drinking,  influence  of,  on  digestibility, 

628 
Dry  matter,  3 

of  body,  composition  of  fat-  and  ash- 
free,  65 

requirements  of,  695 

Drying,  influence  of,  on  digestibility,  623 
Duodenum,  84 


Economy  of  feeding,  influence  of  indi- 
viduality on,  472 
Efficiency  of  body,  544 
as  motor,  544 

compared  with  power  plant,  567 
conditions  affecting,  555 
economic,  562 
gross  and  net,  546 
in  work  of  ascent,  551 

draft,  552 
influence  on, 
of  fatigue,  556 
forms  of  work,  555 
gait,  558 
grade,  559 
individuality,  556 
intensity  of  work,  557 
load,  559 
speed,  552,  557 
training,  556 
mechanical,  545 
over-all,  562 
per  day,  549 
variable,  548,  555 
Efficiency  of  muscle,  545 
Electrolytes,  digestion  of,  101 
Embryo,  net  energy  values  for  growth 

of,  393 

Emulsification  of  fats  in  digestion,  95 
Emulsion  of  fats,  19 
Energy : 
available,  233 
balance  of,  216 
example  of,  240 
in  milk  production,  493,  495 
chemical,  218 

outgo  of,  229,  635 
conservation  of,  219 
definition  of,  216 
expenditure  in, 

internal  work,  measure  of,  256 
feed  consumption,  275 

significance  of,  277 
locomotion,  550 

influence  of  speed  on,  552,  557 
for  work,  body  substance  as  source  of, 

544 

protein  as  source  of,  542 
forms  of,  217 
gross,  227,  635 
income  of,  226 
katabolism  of,  in  fasting,  256 

constancy  of,  256 
kinetic,  218 

measurement  of,  325 


730 


INDEX 


Energy,  —  continued 

outgo  of,  235 
losses  of,  229,  235,  635 
chemical,  299,  635 
in  feces,  230,  635 

fermentation,  230,  636 
computation  of,  627 
heat  production,  235,  650 
urine,  231,  636 
metabolizable,  231,  639 

comparison   of   net   energy   values 

with,  271 
computation  of, 
from  digestible  nutrients,  646 

organic  matter,  648 
factors  for,  234 
for  the  horse,  675 
general  conception  of,  231 
influence  on,  of  amount  of  feed,  664 
method  of  determining,  640 
of  digestible  nutrients,  648 

feeding  stuffs,  642 
real  and  apparent,  645 
significance  of,  645 
synonyms  for,  233 
net.   '(See  Net  Energy) 
outgo  of,  229,  235,  635,  650 
in  combustible  gases,  230,  636 
feces,  230,  635 
heat  production,  235,  650 
urine,  231,  636 

production  values  as  regards,  634 
protein  as  source  of,  318 
rate  of  gain  of,  in  growth,  378 
requirements 
for  fattening,  361 
growth,  399 
of  cattle,  399 
sheep,  401 
swine,  400 
maintenance,  267 
factors  affecting,  304 
influence  on 
of  age,  307 
fattening,  306 
plane  of  nutrition,  305 
stage  of  fattening,  362 
temperature,  304 
manner  of  stating,  283 
methods  of  determining,  281 
modified  conception  of,  284 
of  cattle,  288 
farm  animals,  280,  303 
fowls,  301 
horses,  295 


Energy,  —  continued 
sheep,  292 
swine,  285 

relation  of  temperature  to,  308 
meat  production,  448 
milk  production,  511 
work  production,  562,  564 
sources  of,  for  work,  542     • 
supply,  influence  of,  on  retention  of 

protein,  386 

total,  not  measured  by  heat  of  com- 
bustion, 223 
transformations  of,  218 

in  muscular  contraction,  533 
units,  220 
utilization  of, 
in  growth,  390 

milk  production,  493 
work  production,  544 
values,  net.     (See  Net  Energy  Values) 
Environment,    influence    of,     on    milk 

production,  478 

Enzym  reactions  reversible,  1 50 
Enzyms  as  agents  in  metabolism,  148 
digestive,  78 
extracellular,  148 
intracellular,  149 

in  the  body,  150 
Epithelium,  105 
Erepsin,  79,  87,  98 

action  of,  on  proteins,  98 
Esophagus,  79 
Ether  extract : 
digested,  122 
digestibility  of,  119 
of  feeding  stuffs,  70 
Excretion,  123,  139 

functions  of  kidneys  in,  140 
of  ash  ingredients,  141 
carbon  dioxid,  139 
nitrogenous  products,  140 
water,  142 
Exercise : 

feed  cost  of,  481 

influence  of,  on  meat  production,  457 
milk  production,  480 
yield  of  milk  fat,  482 
Expenditure,  balance  of  income  and,  194 
of    energy   in   horizontal   locomotion, 

.  55° 
Extractives,  percentage  of,  in  lean  meat, 

357 

Farm  animals,  composition  of  bodies  of, 
62 


INDEX 


731 


Fasting : 

energy  katabolism  in,  251 
functions  of  protein  in,  255 
katabolism,  249 
computation  of,  282 
conditions  affecting,  258 
energy  expended  in,  251,  257 
influence  on, 
of  body  fat,  252 

external  temperature,  262,  265 
muscular  activity,  261 
previous  feeding,  253 
size  of  animal,  258 
standing  and  lying,  262 
substances  katabolized,  in,  249 
protein  katabolism  in,  251 
normally  small,  251 
variable,  251 
Fat  and  lean,  proportions  of  in  carcass, 

424 
Fat: 

addition  of,  to  dairy  rations,  517 
animal,  sources  of,  173 
body,  influence  of  on  fasting  katabol- 
ism, 252 

proportion  of  in  offal,  56 
computation  of  gain  or  loss  of,  205 
crude,    determination    of,    in    feeding 

stuffs,  70 

gain  or  loss  of,  205 
manufacture  of,  172 
minimum  of,  for  milk  production,  519 
mobilization  of  reserve,  177 
of  feed,  resynthesis  of,  171 
of  milk,  influence  of  exercise  on  yield 

of,  482 
origin  of,  466 

percentage  of,  in  lean  meat,  356 
milk,  influence  of  feed  on,  528 
milk  solids,  influence  of  feed  on,  529 
production,   protein   unnecessary   for, 

.  363 
proportion  of,  in  meat,  425 

relative   utilization   of   carbohydrates 

and,  for  work  production,  553 

requirements  of,  for  milk  production, 

5i6 

storage  of,  172 
Fatigue,   influence  of,   on  efficiency   of 

body,  556 

milk  production,  482 
Fats,  1 6 

anabolism  of,  171 

animal,  elementary  composition  of,  21 
chemical  changes  in  resorption  of,  108 


Fats,  —  continued 

chemical  reactions  of,  18 

digestion  of,  88,  95 

distinction  between  oils  and,  19 

emulsification  of,  in  digestion,  95 

emulsion  of,  19 

formation  of  carbohydrates  from,  178 
from  carbohydrates,  155,  174 
protein,  168,  173 

functions  of,  186 

hydrolysis  of,  18 

katabolism  of,  176 

melting  points  of,  19 

metabolism  of,  171 

molecular  structure  of,  17 

native,  19 

occurrence  of,  i 

of  milk,  459 

oxidation  of,  at  /3  carbon  atom,  177 

physical  properties  of,  18 

relation  of,  to  growth,  421 

saponification  of,  in  digestion,  96 

specific  effects  of  feeds  associated  with, 

527 
Fattening,  350 

best  age  for,  436 

composition  of  increase  in,  350,  352, 
353,  354,  364 

concurrent,  in  milk  production,  513 

contrast  with  growth,  396 

during  growth,  448 

energy  content  of  gain  in,  361 

energy  requirements  for,  361,  448 

equivalent  energy  values  for,  572 

gain  of  protein  in,  354,  364 

influence  of  condition  on,  438 
on  composition  of  lean  meat,  356 
energy  requirements  for  mainte- 
nance, 306 

net  energy  values  for,  360 

object  of,  358,  427 

of  mature  animals,  350 

pigs,  protein  requirements  of,  411 

protein  requirements  for,  363,  446 

rations,  protein  in,  364 

requirements,  350,  359,  361,  363,  446, 
448 

stage  of,  influence  of,  on  energy  re- 
quirements, 362 

utilization  of  protein  in,  364 
Fatty  acids,  17 
Feces,  105,  109 

as  excretory  product,  109 
feed  residue,  109 

composition  of,  in 


732 


INDEX 


Feces,  —  continued 
losses  of  energy  in,  635 
outgo  of  energy  in,  230 
Feed: 

as  stimulus  to  milk  production,  522 
consumption, 

energy  expended  in,  275 
increases  heat  production,  273 
influence  of, 

on  heat  production,  651 

by  the  horse,  675 
on  metabolism,  651 
influence  on, 
of  age,  431 
breed,  443 
individuality,  443 
significance  of  energy  expenditure  in, 

277 
diminishing    returns    from,    in    milk 

production,  515 
dual  function  of,  183 
influence  of,  on  composition  of  milk, 

527 

quantity  of,  influence  of,  on  digesti- 
bility, 613 

requirements,  691,  693,  694 
for  growth,  396 

maintenance,  280,  313 
meat  production,  445 
milk  production,  500 
supply,  569 

two  aspects  of,  631 
surplus,  disposal  of,  350 
total  amount  of,  for  meat  production, 

449 

unit  system,  logical  basis  of,  595 
units,  593 

comparison    of,    with    net    energy 

values,  596 

utilization  of,  in  milk  production,  488 
Feeding  as  related  to  individuality,  444 
Feeding  standards,  689 
early,  689 
for  meat  production,  451 

the  horse,  566 
Kellner's,  690 
limitations  of,  691 
origin  of,  689 
Wolff's,  689 

modifications  of,  690 
Feeding  stuffs,  571 

accessory  ingredients  of,  632 

significance  of,  632 
choice  of,  703 
classes  of,  72 


Feeding  stuffs,  —  continued, 
classification  of,  571 
composition  of,  66 
determination  of 
ash  in,  67 
crude  fat  in,  70,  71 
crude  protein  in,  68 
nitrogen-free  extract  in,  71 
non-protein  in,  69 
protein  in,  67 
true  protein  in,  67 
water  in,  67 

direct  comparisons  of,  591 
ether  extract  of,  70 
metabolizable  energy  of,  639,  642 
production  values  of,  630,  634,  678 
relative  values  of,  591,  597 
rich  in  carbohydrates,  influence  of,  on 

digestibility,  617 
specific  effects  of,  448 
associated  with  fats,  527 
on  milk  production,  523 
sources  of,  571 
sundry  ingredients  of,  39 
Feeding  trials,  practical,  592 
Fermentation  industries,  by-products  of, 

585 
Fermentation,  losses  of  chemical  energy 

in,  636,  639 
computation  of,  637 
Flavoring  substances,  41 

influence  of,  on  milk  production,  522 
Fluids,  digestive,  78 
Forms  of  work,  influence  of,  on  efficiency 

of  body,  555 
Fowls : 

digestibility  by,  compared  with  swine, 

608 
energy  requirements  for  maintenance 

of,  301 
Fruits,  579 
Fuel  value,  283 
Functions : 

of  ash  ingredients,  187,  190 
carbohydrates,  186 
fats,  1 86 
feed,  dual,  183 

non-nitrogenous  nutrients,  187 
nutrients,  182 

physiological,  597 
proteins,  185 
water,  190 

Gain  in  fattening,    energy   content   of, 
361 


INDEX 


733 


Gain    in    growth,    energy    content    of, 
373 

rate  of,  in  fattening,  influence  of  con- 
dition, 438 
Gait,  influence  of,  on  efficiency  of  body, 

558 

Galactans,  14 
Galactolipins,  23 
Galactose,  9 
Gaseous  exchange  increased  by  work,  540 

through  the  skin,  139 
Gastric  juice,  82 
Gelatinoids,  33 
Germ  meal,  588 
Glands : 

parotid,  79 

salivary,  79 

sublingual,  79 

submaxillary,  79 
Globulins,  33 
Glucose   manufacture,    by-products   of, 

587 
Glucosids,  10 

nitrogenous,  37 
Glutelins,  33 
Gluten  feed,  588 

meal,  588 
Glycogen,  14 

computation  of  gain  or  loss  of,  207 

content  of  body,  61 

conversion  of,  to  dextrose  in  the  liver, 
153 

formation  of,  in  liver,  153 

gain  or  loss  of,  205 

muscle,  154 

storage,  61 
Glycoproteins,  35 
Grade,    influence    of,    on    efficiency    of 

body,  559 

Grain,  influence  of  grinding  on  digesti- 
bility of,  624 
Grasses,  573 

influence  of  maturity  on  composition 

of,  573 

digestibility  of,  574 

Grinding  of  grain,  influence  of,  on  diges- 
tibility, 624 
Gross  energy,  635 
Group  system,  477 
Growth,  371 

ash  requirements  for,  414 

contrast  with  fattening,  396 

energy  requirements  for,  399 

fattening  during,  448 

feed  requirements  for,  396 


Growth,  —  continued 
increase  in,  371 

composition  of,  371 
involves  storage  of  ash,  414 
measure  of,  375 
minimum  of  protein  for,  446 
nature  of,  371 
net  energy  values  for,  390 
of  cattle,  energy  requirements  for,  399 

protein  requirements  for,  404 
sheep,  energy  requirements  for,  401 

protein  requirements  for,  407 
swine,  effect  of  insufficient  protein 

on,  409 

energy  requirements  for,  400 
protein  requirements  for,  408 
protein  requirements  for,  403 

results  in  practice,  403 
rate  of,  373 

at  different  ages,  374 
rate  of  gain  of  energy  in,  378 

protein  in,  375 
storage  of  ash  in,  414 
relation  of  fats  to,  421 
relation  of,  to  age,  373 
relative  values  of  amino  acids  for,  381 

proteins  for,  381 
retention  of  ash  during,  416 
retention  of  protein  in,  382 
influence  of  energy  supply  on,  386 

protein  supply  on,  384 
substances,  41,  348,  422 
total  increase  in,  at  different  ages,  397 
utilization  of  energy  in,  390 
feed  in,  381 

protein  in,  384,  387,  388 
Gums,  15 

Haemoglobin,  135 

Haemoglobins,  35 

Hay  values,  591 

Heart,  125 

Heat  energy,  measurement  of,  221 

unique,  220 

of  combustion,  223,  228 
outgo  of,  235 

production,  causes  of  increase  in,  275 
increased  by  feed  consumption,  273 
influence  on,  of  amount  of  feed,  665 
crude  fiber,  676 
feed  consumption,  651 

by  the  horse,  675 
roughage  compared  with  con- 
centrates, 662 
losses  of  energy  in,  650 


734 


INDEX 


Heavy  feeding,  influence  of,  on  digesti- 
bility, 450 

net  energy  values,  450 
profitable  in  meat  production,  449 
Hemicelluloses,  13 
digestion  of,  92 
Hexosans,  12 
Hexoses,  8 
Hominy  feed,  585 
Horse : 

computation  of  net  energy  values  for, 

675,  676,  677 

digestibility  by,  compared  with  rumi- 
nants, 604 
energy  requirements  for  maintenance 

of,  295 

feeding  standards  for,  566 
influence  of  feed  consumption  on  heat 

production  by,  675 
metabolizable  energy  for,  675 
protein  requirements  of,  for   mainte- 
nance, 329 
Humidity,    influence    of,    on    effects   of 

temperature,  455 

Hydrolysis  of  simple  proteins,  164 
Hydrogen,  losses  of  energy  in,  639 

Ileum,  84 

Improvement  of  a  ration,  computation 

of,  698 
Income,  balance  of  expenditure  and,  194 

of  energy,  226 
Increase : 

composition  of,  198 

influence  of  age  on,  431 

in  fattening, 

composition    of,    350,    352,    353, 

354,  364 

energy  content  of,  352 
protein  in,  364 
growth, 

composition  of,  371 
energy  content  of,  373 
total  at  different  ages,  397 
Individuality : 

feeding  as  related  to,  444 
influence  of 

on  assimilative  power,  441 
course  of  lactation,  473 
digestibility,  609 
digestive  power,  441 
economy  of  feeding,  472 
efficiency  of  body,  556 
feed  consumption,  443 
maintenance  requirements,  442 


Individuality.  —  continued 

meat  production,  440 

milk  production,  514 

net  energy  values,  666 

yield  of  milk,  471 

Ingredients  of  milk,  sources  of,  465 
Initial  and  final  states,  law  of,  223 
Intensity  of  work,  influence  of,  on  effi- 
ciency of  body,  557 
Intercellular  substance,  46 
Intestine,  large,  85 

small,  84 
Inulin,  14 
Invertases,  79,  78 
Investigation,  methods  of,  194 
of  details  of  metabolism,  194 
Ionic  concentration,  maintenance  of,  188 
Iron,  metabolism  of,  181 

occurrence  of,  6 
Isolation,  shelter  from,  457 

Jejunum,  84 
Juice,  intestinal,  87  . 
pancreatic,  86 

Katabolism,  145 

computation  of  per  unit  of  surface,  258 

to  standard  weights,  250 
fasting,  249 

conditions  affecting,  258 
computation  of,  282 
influence  on, 
of  body  fat,  252 

external  temperature,  262,  265 
muscular  activity,  261 
previous  feeding,  253 
size  of  animal,  258 
standing  and  lying,  261 
of  protein  variable,  251 
substances  katabolized  in,  249 
of  carbohydrates,  156 
intermediary,  157 
energy  in  fasting,  251 

constancy  of,  255 
fats,  176 
non-nitrogenous  matter,  influence  of 

work  on,  540 
nucleic  acids,  170 
phosphorus,  180 
proteins,  162 

formation  of  ammonia  in,  165 
nitrogenous  end  products  of,  162 
two  stages  of,  164 
sulphur,  179 
products  of  incomplete,  230 


INDEX 


735 


Katabolism,  —  continued 
protein, 

dependent  on  supply,  322 
in  fasting,  251 

normally  small,  251 
influence  on,  of  feed  supply,  316 

work,  536 
in  work,  influence  of  non-nitrogenous 

nutrients  on,  538 

stimulation  of,  in  milk  production,  515 

Keratins,  33,  57 

Kidneys,  functions  of,  140 

Kind  of  production,  influence  of,  on  net 

energy  values,  666 
Kinetic  energy,  218 
measurement  of,  225 
outgo  of,  235 

Lactase,  79,  87 
Lactation : 

course  of,  influence  of  individuality  on, 

473 
stage    of,    bearing    on    experimental 

methods,  476 

influence  on  composition  of  milk,  476 
milk  production,  476 
yield  of  milk,  476 
Lactose,  n 

origin  of,  467 
Lean  meat,  424 

influence  of  age  on  production  of,  433 

fattening  on  composition  of,  356 
percentage  of  extractives  in,  357 

fat  in,  356 
Lecithins,  22 
Lecithoproteins,  35 
Legumes,  577 
Leguminous  grains,  581 
Levulose,  9 
Ligament,  49 
Lignin,  13 
Linseed  meal,  587 
Lipases,  79,  86 
Lipoids,  1 6 

cell,  formation  of,  172 
nitrogenous,  37 
Live   weight   as   measure   of    nutritive 

effect,  196 
fluctuations  of,  197 
influence  of,  on  effects  of  temperature, 

454 
Liver,  86 

glycogenic  function  of,  152 
Load,  influence  of,  on  efficiency  of  body, 
559 


Locomotion,  energy  expenditure  in,  550 
influence  of  speed,  552,  557 

Magnesium,  metabolism  of,  181 

occurrence  of,  6 
Maintenance,  267 
amino  acids  required  for,  314 
ash  requirements  for,  332 
definition  of,  267 

energy  requirements  for,  267,  280,  303 
factors  affecting,  304 
influence  on 
of  age,  307 
fattening,  306 
plane  of  nutrition,  305 
temperament,  304 
manner  of  stating,  283 
method  of  determining,  281 
modified  conception  of,  284 
relation  of  temperature  to,  308 
matter  requirements  for,  313 
minimum  of  protein  for, 

316,  323 

net  energy  values  for,  271 
of  ash  balance,  339,  344 

cattle,  energy  requirements  for,  288 

protein  requirements  for,  326 
fowls,  energy  requirements  for,  301 
horses,  energy  requirements  for,  295 

protein  requirements  for,  329 
neutrality,  335 
osmotic  pressure,  335 
sheep,  energy  requirements  for,  292 

protein  requirements  for,  327 
swine,  energy  requirements  for,  285 

protein  requirements  for,  329 
optimum  of  protein  for,  323 
protein  requirements  for,  313,  323 

nature  of,  313 

relative  values  of  proteins  for,  315 
requirements,  269 
influence  of  breed,  442 

individuality,  442 
significance    of,    in    interpretation    of 

feeding  experiments,  268 
in  practice,  268 
true  and  live  weight,  280 
value  of  non-protein  for,  324 
Maize,  influence  of  on  metabolism,  664 

proteins,  low  value  of,  681 
Maize  forage,  575 
influence  of  maturity  on  composition 

of,  575 

digestibility  of,  575 
Malt  sprouts,  585 


736 


INDEX 


Maltase,  79,  87 
Maltose,  n 
Manifolds,  80 
Mannose,  9 
Matter : 

balance  of,  202 
dry,  3 

requirements  of, 
for  fattening,  363 
growth,  403,  414 
meat  production,  445 
milk  production,  501,  520 
work  production,  560 
Maturity : 

definition  of,  428 
early,  428 

economic  significance  of,  429 
influence  of  breed  on,  444 
influence  of, 

on  composition  of  grasses,  573 

maize  forage,  575 
digestibility  of  grasses,  574 

maize  forage,  575 
Meat,  definition  of,  424 
fat-free,  composition  of,  52 
proportion  of  fat  in,  425 
Meat  production,  424 
animal  as  factor  in,  428 
combined  growth  and  fattening  in,  448 
energy  requirements  for,  448 
factors  of,  427 
feed  requirements  for,  445 
feeding  for,  444 
feeding  standards  for,  451 
heavy  feeding  profitable  in,  449 
influence  on, 
of  age,  430 
condition,  438 
drinking  water,  455 
exercise,  457    • 
external  conditions,  453 
shelter,  456 
temperature,  453 
nature  of,  424 
processes  involved  in,  426 
protein  requirements  for,  445 
relation  of  conformation  to,  443 

type  to,  443 

total  amount  of  feed  for,  449 
Metabolism,  144 

a  gradual  process,  147 
analytic,  146 
definition  of,  144 
enzyms  as  agents  in,  148 
general  conception  of,  144 


Metabolism,  —  continued 
general  scheme  of,  182 
influence  on,  of  feed  consumption,  651 
investigations,    comparison    of,    with 

balance  experiments,  241 
of  details  of,  194 
of  ash  ingredients,  178 
calcium,  181 
carbohydrates,  152 
fats,  171 
iron,  181 
magnesium,  181 
nucleic  acids,  168 
nucleoproteins,  168 
organic  acids,  159 
pentosans,  158 
pentose  carbohydrates,  157 
phosphorus,  180 
potassium,  181 
proteins,  160 
sodium,  181 
sulphur,  179 
oxidative,  146 

Metabolizable  energy.     (See  Energy) 
Metaproteins,  35 

Methane,  heat  of  combustion  of,  636 
influence  of  amount  of  feed  on  pro- 
duction of,  665 
losses  of  energy  in,  637,  639 
production  of,  in  digestion,  90,  94 
Methods  of  investigation,  194 
Middlings,  buckwheat,  583 

wheat,  583 
Milk: 
ash,  460 

sources  of,  468 
average  composition  of,  461 
carbohydrates,  460 

origin  of,  467 
components  of,  459 
composition  of,  461 
influence  on, 
of  breed,  473 

completeness  of  milking,  480 
feed,  527 

frequency  of  milking,  479 
stage  of  lactation,  476 
variability  in  same  animal,  475 
energy  content  of,  511 
fat,  influence  of  exercise  on  yield  of, 

482 
fats,  459 

origin  of,  466 
glands,  462 

development  of,  463 


INDEX 


737 


Milk,  —  continued 

protein  as  stimulus  to,  502 
influence  of  feed  on  percentage  of  fat 

in,  528 
proteins,  459 

origin  of,  465 
secretion  of,  464 
solids,  composition  of,  influence  of 

breed  on,  474 
influence  of  feed  on  percentage  of 

fat  in,  529 

rate  of  production  of,  469 
sources  of  ingredients  of,  465 
yield  of,  influence  on 

of  completeness  of  milking,  480 
frequency  of  milking,  478 
individuality,  471 
stage  of  lactation,  476 
Milk  production,  459 
a  periodic  function,  476 
animal  as  a  factor  in,  470 
ash  requirements  for,  520 
character  of,  468 
concurrent  fattening  in,  513 
diminishing  returns  from  feed  in,  515 
energy  balances  in,  493,  495 
energy  requirements  for,  511 
factors  of,  469 
fat  requirements  for,  516 
feed  as  stimulus  to,  522 
feeding  a  secondary  factor  in,  500 
feeding  for,  500 
influence  on, 

of  environment,  478 
exercise,  480 
fatigue,  482 

flavoring  substances,  522 
frequency  of  milking,  478 
individuality,  514 
plane  of  nutrition,  514  . 
protein-rich  feeds,  506 
protein  supply,  504,  507 
shelter,  484 
stage  of  lactation,  476 
temperature,  483 

modifying  factors,  484 
minimum  of  fat  for,  519 

protein  for,  501 
net  energy  values  for,  493,  497 

equivalent  fattening  values,  498 
outgo  of  ash  in,  520 
physiology  of,  459 
protein  as  stimulus  to,  502 

requirements  for,  501 
relative  values, of  proteins  for,  492 


Milk  production,  —  continued 
requirements  for,  501 
specific  effects  of  feed  on,  523 
stimulation  of  katabolism  in,  515 
supply  of  ash  in,  521 
utilization  of, 
energy  in,  493 
feed  in,  488 
protein  in,  488 

estimate  of,  489,  491 
Milking,  completeness  of,  influence  of  on 

composition,  480 
yield,  480 

frequency  of,  influence  of  on  composi- 
tion, 479 
yield,  478 
Milling,  by-products  of,  582 

uses  of,  584 
Mineral  matter,  5 
Molasses,  589 
Molasses  feeds,  589 

Molecular  simplification  in  digestion,  103 
Monosaccharids,  8 
composition  of,  8 
Motion,  tissues  of,  50 
Motor,  efficiency  of  body  as,  544 
Mouth,  79 
Muscle  extractives,  37 

fat-free,  composition  of,  52 
mechanical  efficiency  of,  545 
Muscles,  50,  531 
composition  of,  51 
structure  of,  50 
Muscular  work,  nature  of,  531 

Net  energy  below  critical  temperature, 

310 

Net  energy  values,  271,  278,  634,  659 
comparison  of  feed  units  with,  596 

with  metabolizable  energy,  272 
computation  of,  667,  673,  677 
for  the  horse,  675,  676,  677 
from  digestible  nutrients,  667 

organic  matter,  673 
independent   of   chemical   composi- 
tion, 673 

importance  of,  667 
correction  of,  for  crude  fiber,  669 
determination  of,  272 
for  cattle,  659 

different  purposes,  279 
fattening,  360 
growth,  390 
of  embryo,  393 
older  animals,  393 


738 


INDEX 


Net  energy  values,  —  continued 

suckling  animals,  391 
maintenance,  271 
milk  production,  494,  497 

equivalent  fattening  values,  498 
ruminants,  660 
swine,  66 1 

work  production,  563 
influence  on, 
of  age,  666 

amount  of  feed,  664 
breed,  666 
heavy  feeding,  450 
individuality,  666 
kind  of  production,  666 
method  of  determination,  271 
of  digestible  nutrients,  668 
relative,  for  maintenance  and  fatten- 
ing, 361 

Neutrality,  maintenance  of,  189,  335 
Nitrogen  balance,  202 
determination  of,  203 
example  of,  203 
Nitrogen  factors,  69 
Nitrogen-free  extract : 

composition  of  digested,  121 
constituents  of,  72 

determination  of,  in  feeding  stuffs,  71 
Nitrogen,  free,  not  excreted,  202 
Nitrogenous  products,  excretion  of,  140 
Non-nitrogenous  matter : 

influence  of  work  on  katabolism  of,  540 
katabolized  in  work,  nature  of,  542 
of  urine,  159 

origin  of,  1 60 
Non-proteins,  36 

determination  of,  in  feeding  stuffs,  69 

digestion  of,  96,  100 

general  properties  of,  36 

groups  of,  36 

indirect  utilization  of,  622 

influence  of,  on  digestibility,  622 

nitrogen  factors  for,  70 

occurrence  of,  36 

value  of,  324,  684 

for  maintenance,  324 
Nucleoproteins,  34 

metabolism  of,  168 
Nucleus  of  cells,  42 
Nucleic  acids,  34 
digestion  of,  99 
Nutrients : 
digestible,  599 

computation  of,  598 
of  metabolizable  energy  from,  646 


Nutrients,  —  continued 

net  energy  values  from,  667 
metabolizable  energy  of,  648 
net  energy  values  of,  668 
significance  of,  600 
functions  of,  182 
mutual  replacement  of,  270 
non-nitrogenous, 

effect  of  deficiency  of,  320,  324 

surplus  of,  321,  324 
functions  of,  187 
physiological  functions  of,  597 
solution  of,  in  digestion,  101 
Nutrition,  balance  of,  192,  201 

includes  energy,  216 
Nutritive  effect,  live  weight  as  measure 

of,  196 
total,  195 
Nutritive  ratio,  600 

Oat  hulls,  584 

Offal,  composition  of,  55 

proportion  of  body  ash  in,  56 
fat  in,  56 
protein  in,  56 

Oil  extraction,  by-products  of,  586 
Oil  meals,  587 

seeds,  581 
Oils,  distinction  between  fats  and,  19 

ethereal,  40 
Omasum,  80 
Organic  acids,  production  of  in  digestion, 

90 
Organic  matter,  4 

digestible,  computation  of  metaboliz- 
able energy  from,  648 
net  energy  values  from,  673 
subdivision  of,  4 
Osmotic  pressure,  maintenance  of,  188 

335 

Outgo  of  chemical  energy,  229 
in  cutaneous  excretion,  231 
feces,  230 
urine,  231 
heat,  235 

kinetic  energy,  235 
work,  235 

Over-all  efficiency  of  body,  562 
Oxygen : 

absorption  of,  by  blood,  135 

through  skin,  139 
consumption  of,  in  metabolism,  146 

determination  of,  208 
supply  of,  132 
Oxyhaemoglobin,  136 


INDEX 


739 


Packing  house,  by-products  of,  590 

Pancreas,  86 

Parotid  glands,  79 

Passage  of  feed  from  stomach,  83 

Paunch,  80 

Pectins,  15 

Pentosans,  15 

digestion  of,  91 

fermentation  of,  91 

metabolism  of,  158 

proportion  of,  in  crude  fiber,  71 
Pentoses,  9 

metabolism  of,  158 
Pepsin,  79,  82,  96 
Peptids,  30,  35 
Peptones,  35 
Period  system,  477 

Pettenkofer  respiration  apparatus,  212 
Phosphatids,  22,  23 
Phospholipins,  22 
Phosphoproteins,  35 
Phosphorus : 

anabolism  of,  180 

digestion  of,  101 

forms  of,  7,  180,  421 

inorganic,  value  of,  421 

katabolism  of,  180 

metabolism  of,  180 

occurrence  of,  7 
Pigs: 

energy  requirements  of,  400 

feeding  standards  for,  412 

gains  by,  in  growth,  401 

protein  requirements  of,  411 
Plane  of  nutrition,  influence  of,  on  energy 
requirements  for  maintenance, 
305 

milk  production,  514 
Plasma,  blood,  125 
Polypeptids,  31 
Polysaccharids,  n 

chemical  structure  of,  1 1 

terminology  of,  12 
Potassium,  metabolism  of,  181 

occurrence  of,  6 

Power  plant,  comparison  of  body  with, 
567 

efficiency  of,  compared  with  body,  567 
Practical  feeding  trials,  592 
Precipitation,  shelter  from,  456 
Prime  motor,  animal  as,  192 
Production  values, 

as  regards  protein,  678 
energy,  634 

definition  of,  630 
3B 


Production  values,  —  continued 
determination  of,  630 
of  feeding  stuffs,  630  ,634,  678 
Prolamins,  33 
Proteans,  35   . 
Proteases,  79,  86,  87 
Protein : 

addition  of,   influence  of,  on   digesti- 
bility, 622 
as  source  of  energy,  318,  542 

stimulus  to  milk  glands,  502 
body,  fluctuations  of,  319 
proportion  of,  in  bone,  48 

offal,  56 
cause  of    diminished    digestibility  of, 

619 

cleavage,  extent  of,  in  digestion,  98 
computation  of  gain  or  loss  of,  204 
consumed  by  calves,  404 

lambs,  407 
crude,    determination    of,    in    feeding 

stuffs,  68 

digestibility  of,  119 
functions  of,  in  fasting,  255 

work  production,  543,  560 
gain  of,  in  fattening,  354 

or  loss  of,  202 
in  dairy  rations,  506 
fattening  rations,  364 
increase  in  fattening,  364 
influence  of,  on  digestibility  of  rations, 

33i 
insufficient,    effect  of,  on   growth    of 

swine,  409 
katabolism, 

dependent  on  supply,  322 
in  fasting,  251 
variable,  251 
normally  small,  251 
in  work,  influence  of  non-nitrogenous 

nutrients  on,  538 
influence  on,  of  feed  supply,  316 

work,  536 
minimum  of, 
for  growth,  446 

maintenance,  316,  323 
milk  production,  501 
nitrogen  factors  for,  69 
nutrition,  plane  of,  324 
of  feed,  storage  of,  319 
optimum  of,  for  maintenance,  323,  330 
physiological  minimum  of,  254 
production  values  as  regards,  678 
rate  of  increase  of,  in  growth,  375 
retention  of,  in  growth,  382 


740 


INDEX 


Protein,  —  continued 

influence  on,  of  energy  supply,  386 

protein  supply,  384 
requirements, 

computation  of,  to  unit  weight,  325 
for  fattening,  363,  416,  446 
growth,  403 
of  cattle,  404 
sheep,  407 
swine,  408 

results  in  practice,  403 
maintenance,  313,  323 

nature  of,  313 
meat  production,  445 
milk  production,  501 
work  production,  561 
of  cattle,  326,  367,  404,  501 
horses,  329,  561 
sheep,  327,  365,  407 
swine,  329,  368,  408 
relation  of,  to  age,  445 
rich  feeds,  influence  of,  on  milk  pro- 
duction, 506 
supply,  influence  of,  on  digestibility, 

447 

milk  production,  504,  507 
retention  in  growth,  384 
surplus,  katabolized,  317,  488 
true,    determination    of,    in    feeding 

stuffs,  68 

unnecessary  for  fat  production,  363 
utilization  of,  in  fattening,  364 
growth,  384,  387,  388 
milk  production,  488,  491 
limited,  318 
Proteins,  24 

alfalfa,  values  of,  683 
cereal,  values  of,  683 
chemical  changes  in  resorption  of,  107 
coagulated,  35 
coagulation  of,  26 
conjugated,  25,  34 
derived,  25,  35 
primary,  35 
secondary,  35 
digestion  of,  83,  88,  95 
by  erepsin,  98 
pepsin,  96 
trypsin,  97 

formation  of  fat  from,  173 
functions  of,  185 
incomplete,  679 
maize,  low  value  of,  681 
nomenclature  of,  24 
of  milk,  459 


Proteins,  —  continued 

origin  of,  465 
physical  properties  of,  25 
putrefaction  of,  99 
relative  values  of,  678 
for  growth,  381 
maintenance,  315 
milk  production,  492 
simple,  25,  26 
anabolism  of,  160 
classification  of,  32 
cleavage  products  of,  28 
composition  of,  26 
deaminization  of,  165 

reversible,  166 
formation  of, 

ammonia  in  katabolism  of,  165 
carbohydrates  from,  167 
fat  from,  168 
hydrolysis  of,  28,  164 
katabolism  of,  162 
metabolism  of,  160 
nitrogenous  end  products  of  katab- 
olism of,  162 

non-nitrogenous  residue  of,  163 
proportions  of  cleavage  products  in, 

3i 

structure  of,  27 
synthesis  of,  30 

from  digestive  products,  160 
two  stages  in  katabolism  of,  164 
unbalanced,  679 
Proteoses,  35 
Protoplasm,  42 

composition  of,  44 
Ptyalin,  78,  79 

conditions  of  action  of,  92 
Pulmonary   exchange,   investigation   of, 

214 

Putrefaction  of  proteins,  99 
Pylorus,  83 

Quantity  of  feed,  influence  of,  on  diges- 
tibility, 613 
Quotient,  respiratory,  207 

Raffinose,  n 

Rate  of  growth,  373 

at  different  ages,  374 
Rations : 

compounding  of,  707 
computation  of,  565,  689,  697 
from  given  feeding  stuffs,  700 
improvement  of,  698 
for  work  production,  calculation  of,  565 


INDEX 


741 


Rectum,  85 

Regnault-Reiset   respiration   apparatus, 

209 
Relative  values  of  feeding  stuffs,   591, 

597 

Requirements : 

for  fattening,  350,  359,  361,  363 
growth,  396,  399,  403,  414 
maintenance,  269,  280,  313,  332 
meat  production,  444,  445,  448 
milk  production,  500,  501,  511,  520 
work  production,  560,  562 
of  ash, 

for  growth,  414 
maintenance,  332 
milk  production,  520 
work  production,  562 
dry  matter,  696 
energy  for  fattening,  361 
growth,  399 
maintenance,  280,  303 
meat  production,  448 
milk  production,  511 
work  production,  562,  564 
feed,  691,  693,  694 
fat  for  milk  production,  516 
protein  for  fattening,  363 
growth,  403 
maintenance,  313,  323 
meat  production,  445 
milk  production,  501 
work  production,  561 
Residue,  non-nitrogenous,  of  simple  pro- 
teins, 163 
Resorption,  105 

chemical  changes  in,  107 
mechanism  of,  106 
paths  of,  107 
role  of  osmosis  in,  106 
Respiration,  123,  132 
apparatus,  208 
Pettenkofer,  212 
Regnault-Reiset,  209 
calorimeters,  236 
influence  of  work  on,  536 
of  tissues,  136 
regulation  of,  137 
Respiratory  quotient,  207 
Reticulum,  80 

Reversible  reactions,  150,  166 
Reversibility  of  metabolic  reactions,  152, 

i53 

Rhamnose,  9 
Rice  bran,  583 
polish,  583 


Roots,  73,  579 

influence  of,  on  digestibility,  618 
Roughage,  72,  572 

comparison  of,  with  concentrates,  662 

general  character  of,  572 

influence  of  cutting  on  digestibility  of, 

624 
proportion  of,   to   concentrates,   451, 

696 
proportion   of   vegetative   organs  in, 

576 

Rumen,  80 

Ruminants,   digestibility  by,   compared 
with  horses,  604 
swine,  606 
species  of,  603 
net  energy  values  for,  660 
Rumination,  81 
Rye  bran,  582 

Saliva,  79 

action  of,  in  stomach,  73 

on  starch,  92 

Saponification  of  fats  in  digestion,  95 
Schematic  body,  195 
Scleroproteins,  34 
Sheep : 

digestibility  by,  compared  with  horse, 

604 

swine,  606 
energy  requirements  for  growth,  401 

maintenance,  292 
influence  of  feed  consumption  on  heat 

production  by,  653 

maintenance    requirements    of,    com- 
pared with  cattle,  294 
protein  requirements  for  growth,  407 

maintenance,  456 
Shelter  from  precipitation,  456 
sun,  457 
wind,  456 
influence  of,  on  meat  production,  456 

milk  production,  484 
Size  of  animal,  influence  of,  on  fasting 

katabolism,  258 
Skeleton  as  reserve  of  ash  ingredients, 

338       • 

Skin,  gaseous  exchange  through,  139 
Slaughter  tests,  comparative,  199,  351 
Sodium,  metabolism  of,  181 

occurrence  of,  6 

Solution  of  nutrients  in  dige'stion,  101 
Species,  influence  of,  on  digestibility,  603 

of  ruminants,  digestibility  by,  603 
Specific  dynamic  action,  275 


742 


INDEX 


Specific  effects  of  feeds,  448 
associated  with  fats,  527 
on  milk  production,  523 
Speed,    influence    of,    on    efficiency    of 

body,  552,  557 
on  energy  expenditure  in  locomotion, 

552,  557 
Standing    and    lying,    influence   of,    on 

fasting  katabolism,  261 
Starch,  13 

digestion  of,  79,  88,  92 
in  intestines,  94 

stomach,  93 

fermentation  of,  in  digestion,  94 
manufacture,  by-products  of,  587 
values,  672 
Steapsin,  79,  86 
Stomach,  79 
of  hog,  81 
horse,  81 
ruminants,  80 
sheep,  80 

passage  of  feed  from,  83 
Straw,  577 
Suckling  animals,  net  energy  values  for 

growth  of,  391 
Sucrase,  79,  87 
Sucrose,  10 
Sugar  beet  pulp,  589 
Sugar  manufacture,  by-products  of,  588 
Sulphur, 

digestion  of,  101 
katabolism  of,  179 
metabolism  of,  179 
occurrence  of,  7 
Sun,  shelter  from,  457 
Sundry  ingredients  of  animals,  39 

plants,  40 
Surface,  computation  of, 

computation  of  katabolism  per  unit 

of,  258 

Surplus  feed,  disposal  of,  350 
Swine : 

digestibility  by,  compared  with  fowls, 

608 

ruminants,  606 
effect  of  insufficient  protein  on  growth 

of,  409 
energy  requirements  for  growth,  400 

maintenance,  285 
influence  of  feed  consumption  on  heat 

production  by,  653 
net  energy  values  for,  66 1 
protein  requirements  for  growth,  408 
maintenance,  329 


Synthesis 

of  hippuric  acid,  163 
nucleic  acids,  169 

simple  proteins  from  digestive  prod- 
ucts, 1 60 
seat  of,  161 
uric  acid,  171 
Synthetic  processes  in  the  body,  146 

Tankage,  590 
Temperature, 

body,  chemical  regulation  of,  263 

physical  regulation  of,  262 
critical,  264,  453 

lowered  by  feed  consumption.  308 
effects  of  extremes  of,  266 
external,  influence  of  age,  on  effects  of, 

454 

amount  of  ration  on  effects  of,  454 
humidity,  on  effects  of,  455 
live  weight  on  effects  of,  454 
influence  of,  on  fasting  katabolism, 

262,  265 

energy  requirements  for  mainte- 
nance, 304 
meat  production,  453 
milk  production,  483 
modifying  factors,  484 
of   drinking   water,    influence   of,   on 

meat  production,  455 
relation  of,  to  energy  requirements  for 

maintenance,  308 
Tendon,  49 
Tissue,  adipose,  58 

composition  of,  59 
Tissues : 
animal,  45 

classification  of,  45 
connective,  49 
elastic,  49 
epidermal,  57 

composition  of,  57 
functions  of,  57 
of  alimentation,  54 

chemical  composition  of,  55 
motion,  50 
reserve,  58 
supporting,  46 
Tonus,  534 
Total    feed    required,   computation    of, 

697 
Training,  influence  of,  on  efficiency  of 

body,  556 
Triglycerids,  17,  19 
elementary  composition  of,  20 


INDEX 


743 


Trisaccharids,  n 
Trypsin,  79,  86,  97 
Tubers,  73,  579 

influence  of,  on  digestibility,  618 
Type,  relation  of,  to  meat  production, 
443 

Units  of  energy,  220 
equivalence  of,  221 
Urea,  162 

antecedents  of,  162 

Urine,  losses  of  chemical  energy  in,  636 
non-nitrogenous  matter  of,  159 

origin  of,  160 

outgo  of  chemical  energy  in,  231 
Utilization : 

of  energy  in  growth,  390 
milk  production,  493 
feed  in  growth,  381 

milk  production,  488 
non-proteins,  686 
proteins,  in  growth,  384,  387,  388 
milk  production,  488 

estimates  of,  489,  491 
meaning  of,  488 

relative,  of  fats  and  carbohydrates  for 
work  production,  553 

Veins,  126 
Villi,  105 
Vitamins,  41,  348 

Water: 

balance  of,  216 

determination    of,   in    feeding    stuffs, 

67 
drinking,  influence  of,  on  digestibility, 

628 

meat  production,  455 
excretion  of,  142 
functions  of,  3,  190 
supply,  458 
Waxes,  21 

Weight.     (See  Live  weight) 
Wheat  bran,  582 
Wind,  shelter  from,  456 


Work: 

analysis  of,  500 
body  substance  source  of  energy  for, 

544 
forms  of,  influence  of,  on  efficiency  of 

body,  555 
influence  of, 

on  circulation,  535 
digestibility,  610 
gaseous  exchange,  540 
katabolism     of     non-nitrogenous 

matter,  540 
protein,  536 
respiration,  536 
intensity  of,  influence  of,  on  efficiency 

of  body,  557 
internal,  256 
measure    of    energy    expended    in, 

256 

muscular,  nature  of,  531 
nature     of     non-nitrogenous     matter 

katabolized  in,  542 
of  ascent,  551 

efficiency  of  body  in,  551 
of  digestion,  277 

differences  between  feeding  stuffs,  663 
roughage  compared  with  concentrates, 

662 

draft,  552 

efficiency  of  body  in,  552 
outgo  of,  235 

protein  as  source  of  energy  for,  542 
secondary  effects  of,  535 
sources  of  energy  for,  542 
Work  production,  531 
ash  requirements  for,  565 
calculation  of  rations  for,  565 
energy  requirements  for,  562 
feed  requirements  for,  560 
functions  of  protein  in,  543,  560 
net  energy  values  for,  563 
physiology  of,  531 
protein  requirements  for,  561 

Xylan,  15 
Xylose,  9 


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'HE   following   pages   contain   advertisements   of 
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Principles  of  Feeding  Farm  Animals 

BY  SLEETER   BULL 

Associate  in  Animal  Nutrition,  University  of  Illinois 

i2mo,  illustrated,  $1-75 

This  volume  is  an  outgrowth  from  a  class  manual  written  for  the 
author's  students  in  a  general,  elementary  course  in  stock  feeding. 
The  scientific  facts  underlying  the  art  of  feeding  animals  have  been 
presented  in  such  a  manner  that  the  book  will  not  only  be  suitable 
for  use  as  a  text  for  college  courses  in  general  feeding,  but  will  also 
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The  author  first  discusses  the  scientific  aspects  of  the  subject, 
presenting  them  in  a  simple,  concise  manner.  Following  that  are 
presented  rather  definite  rules  regarding  the  feeding  of  the  different 
classes  of  livestock  which,  taken  in  connection  with  the  feeding 
standards  and  the  discussion  of  the  nutritive  value  of  the  different 
feeds,  should  enable  the  inexperienced  feeder  to  formulate  satis- 
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are  specific  rather  than  general.  A  large  number  of  valuable  illus- 
trations and  tables  have  been  included. 

Instead  of  devoting  separate  chapters  to  the  feeding  of  the  different 
classes  of  farm  animals  the  author  has,  in  order  to  avoid  duplication, 
discussed  separately  the  use  of  each  of  the  principal  feeds  for  the 
different  species  and  classes  of  livestock.  For  example,  under  the 
discussion  of  corn,  its  use  is  given  in  the  rations  of  growing  cattle, 
colts,  pigs  and  lambs;  fattening  cattle,  hogs  and  sheep;  breeding 
cattle,  horses,  hogs  and  sheep,  dairy  cows,  and  work  horses. 

In  addition  to  the  discussion  of  the  nutritive  value  of  feeds  and 
rations,  the  author  has  also  given  particular  attention  to  their  ferti- 
lizing values,  a  phase  which  is  often  neglected  both  by  the  student  and 
the  stockman. 


"The  book  ought  to  be  in  the  library  of  every  farmer."  —  Farmer's 
Mail,  Topeka. 

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the  author  desires  to  reach,  namely,  the  student  and  the  feeder." 
—  Journal  American  Chemical  Society,  Washington,  D.C. 


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The  Feeding  of  Animals 

BY  WHITMAN  HOWARD  JORDAN 

Director  of  the  New  York  Agricultural  Experiment  Station  at  Geneva 
New  Edition,  Revised,  and  Entirely  Reset 

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This  volume  has  been  revised  to  incorporate  the  more 
recent  knowledge  concerning  animal  nutrition  and  to  or- 
ganize the  text  into  a  more  convenient  form  for  student 
use. 

As  with  the  former  edition,  the  text  is  divided  into  two 
parts :  Part  I  deals  with  the  general  principles  of  bio- 
chemistry that  bear  upon  animal  nutrition.  Part  II  gives 
the  practical  side  of  feeding  animals  with  such  attention 
to  principles  as  relate  specifically  to  the  nutrition  of  the 
various  classes  of  farm  animals.  By  this  arrangement  the 
volume  will  be  useful  for  classroom  work  with  those  stu- 
dents who  have  given  little  or  no  attention  to  bio-chemistry 
as  such,  at  the  same  time  serving  the  interest  of  those 
students  who  have  given  considerable  attention  to  chemical 
studies.  The  farmer  and  general  reader  will  also  find  the 
treatise  helpful  in  the  practice  of  animal  husbandry. 


"A  valuable  contribution  to  agricultural  literature. 
Not  a  statement  of  rules  or  details  of  practice,  but  an 
effort  to  present  the  main  facts  and  principles  fundamental 
to  the  art  of  feeding  animals."  -  New  England  Farmer. 

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around."  —  Farm  Stock  Home,  Minneapolis. 


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The  Scientific  Feeding  of  Animals 

BY  PROFESSOR  O.  KELLNER 


AUTHORIZED  TRANSLATION  BY 

WILLIAM  GOODWIN,   B.Sc.,   PH.D. 

Lecturer  on  Agricultural  Chemistry,  and  Head  of  the  Chemical  Department, 
South-Eastern  Agricultural  College  (University  of  London),  Wye,  Kent. 


Cloth,  I2mo,  $1.75 

An  authorized  English  translation  of  the  valuable  work 
of  Dr.  O.  Kellner.  It  explains  in  simple  language  the 
general  laws  which  underlie  the  feeding  of  animals  and  the 
scientific  foundations  upon  which  the  principles  of  animal 
nutrition  rest.  

"I  wish  to  say  that  it  is  one  of  the  most  valuable  books 
in  the  English  language  on  Feeding  Farm  Animals.  The 
author  is  extremely  lucid  in  expression  and  concise  in 
statement.  He  covers  his  field  in  a  manner  that  is  well 
planned  and  such  as  will  give  the  reader  a  most  excellent 
knowledge  of  the  general  principles  of  feeding."  -  PRO- 
FESSOR CHARLES  S.  PLUMB,  Ohio  State  University. 

"Dr.  Kellner 's  standing  as  a  student  and  investigator 
in  this  subject  is  too  high  for  any  words  of  commendation 
to  be  needed,  and  I  feel  sure  that  the  translator  and  pub- 
lisher have  done  a  service  in  rendering  this  work  available 
to  English  and  American  students."  -  PROFESSOR  HENRY 
P.  ARMSBY,  Pennsylvania  State  College.  • 


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The  Breeding  of  Animals 

BY  F.   B.   MUMFORD,   M.S. 

Professor  of  Animal  Husbandry,  Dean  of  the  College  of  Agriculture,  and  Director 
of  the  Experiment  Station  of  the  University  of  Missouri. 

I2mo,  illustrated,  304  pages,  $1.75 

This  text-book  deals  first  with  the  fundamental  questions  of  in- 
heritance common  to  plants  and  animals,  but  emphasizes  the  prin- 
ciples, methods  and  practices  which  are  peculiar  to  animal  breeding. 

The  improvement  of  the  domestic  animal  resulting  in  the  develop- 
ment of  highly  specialized  qualities  useful  to  man  is  one  of  the  most 
notable  achievements  in  modern  agriculture.  How,  through  man's 
efforts,  these  highly  specialized  and  valuable  qualities  have  been 
acquired,  and  how  these  qualities  have  come  to  be  represented  in 
the  constitution  of  the  germplasm  and  thus  transmitted  from  parent 
to  offspring,  is  a  subject  of  great  scientific  and  practical  interest. 

The  scientific  principles  which  govern  the  practice  of  animal 
breeding  may  all  be  classified  under  inheritance,  reproduction  and 
development.  The  text  emphasizes  particularly  those  scientific  prin- 
ciples which  are  recognized  as  the  basis  of  heredity  and  which  have 
been  sufficiently  well  established  to  afford  a  real  basis  for  the  practice 
of  animal  breeding.  The  physical  basis  of  heredity  in  the  germplasm 
of  the  cell  and  the  significant  changes  resulting  in  transmission  are 
described  and  illustrated. 

The  physiology  of  reproduction  and  its  applications  to  the  practice 
of  breeding  is  the  subject  of  an  important  chapter.  The  interrela- 
tions of  heredity  and  development  which  constitute  the  real  basis 
of  the  breeder's  art  are  discussed.  The  practical  questions  of  in- 
breeding, crossbreeding,  grading,  fertility,  sterility,  and  sex  are  con- 
sidered in  the  light  of  the  most  modern  development  of  biological 
science. 

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